Abstracts of papers by Hans Machemer and coworkers
Abstracts 1 - 30
30
Are receptor-activated ciliary motor
responses mediated through voltage or current?
We have examined the crucial signals transmitted from the mechanoreceptive
regions to the locomotory cilia of the unicellular organism Stylonychia. We report here that these signals are
potentials of either polarity. This is
the first report of intracellularly recorded receptor currents in
ciliates. We conclude that activation of
the ciliary motor response through mechanical stimuli involves the following
steps: (1) increase in conductance of the somatic sensory channel; (2) passive
spread of the receptor potential in to the cilium; (3) conductance modification
of the voltage-sensitive Ca2+ channel; (4) change in intraciliary Ca2+
concentration; (5) Ca2+-dependent activation of the ciliary axoneme.
29
Hyperpolarizing and depolarizing
mechanoreceptor potentials in Stylonychia.
The surface of a Stylonychia cell
was mechanically stimulated with a piëzo-crystal driven micro-needle of 0.5 to
2µm distal diameter and maximal amplitudes of 13µm. Stimulation of the anterior surface of the
cell produced a membrane depolarization, whereas stimulation of the posterior
surface elicited a hyperpolarizing response.
The analysis of electric responses to mechanical stimuli, driven by
pulses varied in duration, amplitude, rate and acceleration, revealed that the
hyperpolarizing receptor potential (hRP) rose in parallel with the stimulus
velocity. Stimulus amplitudes beyond
12µm amplitude and rates larger than 4mm/s did not increase the amplitude of
the membrane response. Sustained stimuli
slowed down the repolarization to the resting level. Adaptation of the receptor response was seen
with small and sustained velocities of the stimulating probe. The depolarizing receptor response (dRP)
triggered an action potential consisting of two regenerative components, one
graded, the other all-or-none. Positive
conditioning current pulses reversed the polarity of the dRP which was
primarily Ca-dependent (22,4mV/log [Ca]o).
The dRP was isolated from the action potential by negative membrane
conditioning. The reversal potential of
the hRP was negative of the resting potential and completely K-dependent
(58,5mV/log [K]o). Submaximal hyperpolarizing and subthreshold depolarizing receptor potentials
showed summation. No refractoriness of
the hRP was detected. Summation of
depolarizing responses beyond the threshold activated a regenerative membrane
depolarization.
28
Membrane excitability in Stylonychia: Properties
of the two-peak regenerative Ca-response.
Spontaneous or stimulus-induced membrane
depolarizations in Stylonychia reveal
two components of the action potential, a fast (peak I) and a slow response
(peak II). Current stimuli of sufficient
magnitude (e.g. 3x10-8A, 2ms) to evoke maximal responses were given
to characterize the time-, voltage- and ion dependence of both regenerative components. The threshold voltage is 2-3mV above resting
potential. Peak I is graded with
stimulus intensity, peak II is all-or-none reaching commonly less than ½ of
peak I maximal amplitude. The
refractoriness of peak II exceeds that of peak I at given stimulus
intervals. Refractory periods of both
components decrease with increased stimulus strength. Depolarizing prepulses depress peak II prior
to a depression of peak I, the latter being more sensitive that peak II to
depression by hyperpolarizing current conditioning. Increasing [K]o with [Ca]o held constant leaves peak potentials I and II
largely unaffected. Rising [Ca]o at constant [K]o increases peak
potentials I by 17mv, peak potentials II by 10mV per 10-fold increase in [Ca]o. Replacement of chloride by nitrate or
proprionate indicates no contribution to the membrane potential of
chloride. Considerations of the
calcium/potassium conductance ratios suggest that both components of the
regenerative response arise from potential-dependent inward calcium fluxes
which are strongly short-circuited by outward fluxes of potassium.
27
Swimming sensory cells: Electrical
membrane parameters, receptor properties and motor control in ciliated
protozoa.
Present experimental work on the
sensory-motor system in ciliates is following up several lines of protozoan
research dating back to the beginning of this century. Intracellular recording of membrane
potentials in Paramecium, pioneered
by Kamada (1934), led to the finding of graded action
potentials preceding ciliary reversal. Evidence shows that passive and active
membrane properties in ciliates are predominantly determined by the
conductances of K- and Ca-concentration batteries. Paramecium
caudatum produces a single action potential as a response to depolarizing
stimuli. The composite action potential
in Stylonychia mytilus
is elicited by depolarization through spontaneous pacemaker activity or
external stimulation. Excitability and
motor behaviour were shown to be modified in certain membrane mutants of the
autogamous Paramecium aurelia. Externally applied potential gradients evoke
direct cathodal orientation and “guided” swimming in Paramecium and other ciliates which is explained on
electrophysiological grounds. On the
other hand, the topic response of Paramecium
to gravity awaits additional experimental examination in order to test three
physical and one physiological hypotheses of negative geotaxis. Anterior mechanical stimulation depolarized,
but posterior stimulation hyperpolarizes the membrane due to activation of
Ca-channels or K-channels, respectively.
The depolarizing receptor potential commonly elicits the action
potential. Hyperpolarizing and
depolarizing receptor potentials are different from regenerative membrane
responses in that they summate in the absence of refractoriness. Orientation of various ciliates in chemical
gradients and “recognition” of food materials suggest a highly selective
chemosensitivity. Local and overall
thermal sensitivity have been demonstrated in Paramecium. The ciliary
motor activity is correlated with the membrane potential. Upon depolarization the beat orientation of the
cilia is reversed toward the cell anterior, and cyclic
beating frequency increases.
Hyperpolarization induces the cilia to beat more posteriorly in conjunction
with increases ciliary frequency.
ATP-reactivation experiments with demembranated paramecia and
electrophysiological evidence indicate that the intraciliary ionic
Ca-concentration controls both beat orientation and frequency of the
cilia. Intraciliary Ca is regulated
through the voltage-sensitive Ca-conductance of the membrane which couples ciliary
activity to electric membrane responses.
Changes in the ionic environment of the cell shift the membrane
potential, but the ciliary motor activity returns to previous levels after a
few minutes of equilibration in the new medium.
This accommodation is probably due to a resetting of [Ca]i to the standard
resting value. The mechanism by which
[Ca]i controls
the ciliary machine is unknown. In
summary, sensory-motor coupling involves two processes commonly separated in
multicellular organisms: sensory transduction and electro-mechanical
coupling. In ciliates each stimulus
which modifies the membrane potential implicates changes in the Ca-conductance
of the ciliary membrane which directly affects the working of the underlying
ciliary machine.
Contents.
Introduction – Passive electric membrane properties – Ca action
potentials – Membrane mutants – Responses to external potential gradients –
Negative geotaxis – Sensitivity to brief mechanical stimuli – Inactivation upon
contact – Effects of local and overall stimuli – Food recognition – Thermal
sensitivity – Control of the orientation of the ciliary power stroke – Ciliary
frequency control – Direct Ca2+ application to the ciliary apparatus
– Stabilizing effects of ciliary activity – The cilium as a receptor-effector –
Behavioural consequences.
26
Electromechanical coupling of ciliary
activity in Paramecium (Filmkommentar).
The film includes three parts: 1. Constant current stimulation; 2.
Suppression of the reversal of ciliary beating during clamped voltage steps; 3.
Graded frequency and directional responses of cilia in response to slow voltage
ramps during voltage clamp.
25
Motor activity and bioelectric control
of cilia.
An overview is given of basic molecular elements of the ciliary machine, its
function in 3 dimensions and time, the coordination of cilia as regularly
arranged in the cellular surface membrane, and the bioelectric control of the
ciliary beating frequency and orientation.
At the basis of available data, four largely assumptions are made: (1) The cilium is a unidirectional rotary sliding machine. (2)
The sliding machine produces a cyclic motion in 3 dimensions which is polarized
in time as well as in space. (3) The cyclic pattern of ciliary motion occurs
with a certain frequency being coupled to a certain beat direction, and this
pattern can be rotated over an angle of about 180°. (4) The direction and frequency of ciliary
beating are determined by the concentration of the membrane-regulated
intracellular messenger substance, calcium.
24
Interactions of membrane potential and
cations in regulation of ciliary activity in Paramecium.
Ciliary activity in Paramecium was
investigated in different external solutions using techniques of voltage clamp
and high frequency cinematography. An
increase in the external concentration of K, Ca, or Mg ions depolarized the
resting potential; no effect on ciliary activity was observed. When the membrane potential was fixed under
voltage clamp, an increase in external Ca or Mg and, to a lesser extent, an
increase in K concentration, raised the frequency of normal beating or
decreased the frequency of reversed beating of the cilia. Similar effects resulted from membrane
hyperpolarization under constant ionic conditions. An increase in concentration of Ca, but not
of Mg or K, enhanced hyperpolarization-induced
augmentation of ciliary frequency. An increase
in Ca concentration also specifically augmented the delayed increase in inward
current during rapid hyperpolarization.
The results support the view that [Ca2+]i regulates the frequency and direction
of ciliary beating. It is suggested that
the insensitivity of the ciliary motor system to elevations of the external ion
concentration results from compensation of their effects on [Ca2+]i.
23
Calcium in the bioelectric and motor functions of Paramecium.
An overview of the recent research on the Paramecium sensory-motor system including 8 figures from published
papers and 4 more summarizing illustrations. Introduction: ‘Paramecium offers special advantages for
biophysical, genetic, and molecular biological approaches to problems of
membrane organization and function and the regulation of cell motility by the
surface membrane. This ciliate has a
combination of features which facilitate a multidisciplinary approach. As a unicellular microorganism which has
bioelectric properties resembling muscle and nerve, it manifests its membrane
responses while swimming free in culture through its locomotor responses to
various chemical stimuli, and it is susceptible to both genetic and
electrophysiological manipulation. In a
series of recent studies we have found that Ca2+ is of central importance
in several roles in the bioelectric and locomotor functions of Paramecium. Since the ciliates are evolutionary distant
from excitable metazoan tissues such as nerve and epithelium, etc., it is
especially interesting that Ca2+ appears in these lower forms as a
highly adapted regulatory agent performing akin to those it performs in
metazoan cells.
22
Ciliary frequency and orientational responses to clamped voltage steps in Paramecium.
Simultaneous voltage clamping and microcinematography were used to examine
the behaviour of cilia in response to maintained hyperpolarizing and
depolarizing steps of the membrane potential of Paramecium caudatum. In the absence of stimulation the cilia beat at less than 20 cycles per second with
the power stroke directed toward the posterior and to the right (i.e. 4 o’clock)
of the cell. Hyperpolarization of the membrane results in a graded increase in frequency and a slight clockwise shift in orientation of the power stroke to a more posteriad orientation (i.e. 6 o’clock); peak frequencies of up to 50 Hz occur after about 4 s, after which the beating settles to a reduced steady frequency. Responses to depolarization are more complex. Below +3 to +5 mV the frequency of the cilia drops toward a minimum. Further depolarization up to +20 mV produces a stimulus-graded increase in frequency with a graded counterclockwise shift in orientation of the power stroke. Reversed beating frequency increases during maintained depolarizations over several seconds and then gradually decreases over a period of 30 to 60 s; during this time ciliary beat orientation also relaxes toward the normal direction (4 o’clock). With potential shifts exceeding + 60 mV the frequency of reversed beating drops reaching a minimum between +80 and +100 mV. Normal ciliary beating is
re-established at even more positive potential steps. During 1-2s voltage steps of small (1-4 mV) or very large positive potential steps (60-100 mV) there is a continuing slowing down of normally directed beating until the cilia stop and eventually exhibit reversed beating. Ciliary orientation and frequency change in conjunction as a function of the membrane voltage. Following the first second of stimulation, these tow movement parameters also exhibit changes in parallel with changes in membrane current. This suggests a common regulating principle. Evidence is discussed indicating that the common agent is the
intracellular concentration in ionic calcium as being regulated by the voltage-sensitive calcium conductance of the surface membrane.
21
Modification of ciliary activity by the rate of membrane potential changes in Paramecium.
The sequence of ciliary responses in Paramecium following shifts in membrane potential is rate-dependent. With depolarizations exceeding the rate of 40 mV/s the cilia switch directly from normal to reversed beating, thereby rapidly increasing their beating frequency. When the membrane is depolarized at the rate of 40 mV/s, unabbreviated ciliary responses occur with the following sequence: reduction in normalbeating → inactivation → increase in reversed beating. This potential-correlated sequence is at least 50 times slower than the preceding electric membrane response. A time-dependent hysteresis of current versus voltage during depolarizing and hyperpolarizing slow voltage ramps suggests a mechanism of membrane accomodation. A slow inactivation of inward calcium current during depolarization, and a slow decrease in Ca-conductance during hyperpolarization is suggested from a hysteresis of the frequency response versus membrane voltage. Differences in local ciliary responses to slow voltage ramps are interpreted as generated by varying local
Ca-conductances. It is concluded that the graded frequency and directional responses of the cilia are correlated with the time-course of calcium accumulation and depletion within the cilium.
20
Regulation of ciliary beating frequency
by the surface membrane.
Report on the results of several papers on the causal relationship between
the membrane potential and the ciliary motor response of freshwater protozoans
(Paramecium, Euplotes) with Ca2+
as the presumed intracellular messenger substance. It is proposed that the increase in ciliary
frequency is a function of rising as well as extreme decrease in the calcium
membrane conductance.
19
Mechanical conditions of flagellar and
ciliary metachronism.
A brief report of the geometric and hydromechanical
conditions leading to metachronism in flagella and cilia including a few
figures illustrating the relationship between individual oscillators and the
resulting interciliary (interflagellar) coordination.
18
Frequency and directional responses of
cilia to membrane potential changes in Paramecium.
Ciliary motor reactions and membrane responses to injected current
stimulation in Paramecium caudatum
were recorded with a combined electrophysiological and high-speed ciné system
to investigate relations between ciliary activity and membrane potential. The power stroke of the cilia normally
directed to the right and rear of the cell rotates clockwise to a more
posteriad orientation in response to hyperpolarizing stimulation. Depolarization induces a counterclockwise
shift of the power stroke, usually leading to the rapid reversal of beat
direction toward the anterior cell end.
Ciliary beat frequency is increased either with hyperpolarization or
with moderate or strong depolarization of the membrane. The frequency response is linked to the
directional response in such a way that minimal frequency occurs during
transition from reversed to normal beating.
With increasing clockwise or counterclockwise angular deviation of the
power stroke from this sector of transition, the beating frequency is
increased. In the course of transition
from the reversed to normal beating the cilia in inactivated, i.e. they stick
out perpendicularly to the cell surface and exhibit no polarized beat. A depression in normal beating activity
resembling inactivation occurs with small depolarization of the membrane. The role of transmembrane Ca fluxes and
consequent modification of intraciliary calcium concentrations is considered
with regard to the observed ciliary responses.
17
Ciliary activity and metachronism in
protozoa.
A review article covering research on the relationship between ciliary
activity and metachronism from 1842 to 1973 with the following conclusion: ‘All
flagellate and ciliate protozoa exhibiting metachronal coordination show, as
far as is known, specific relations between the physical parameters of the
oscillating units and the wave system.
Differences between symplectic metachrony seen in the flagellates, and
dexioplexy prevailing in ciliates are not fundamental in nature, since forms of
transition are produced in a single cell at different viscosities. The relationship between forces generated by
a flagellum or cilium and the resulting metachronism is so close that neuroid
mechanisms of coordination are rendered superfluous. Among mechanical hypotheses on the generation
of metachronism the concept of continuous
mechanical interference is the most promising one allowing a detailed
understanding of the properties of an observed metachronal system. Possible involvement of mechanical triggering
in establishing phase relationships cannot be excluded. Temporal and local modifications of
metachronism may be understood as determined by membrane-controlled ciliary
activity. From an evolutionary point of
view, the dexioplectic metachronism may have been developed from symplectic
forms of coordination by a progressive polarization of the counterclockwise flagellar
beating accompanying the reduction in length of the ciliary shaft.
16
Electrophysiological control of reversed
ciliary beating in Paramecium.
Paramecium immersed in freshwater
solution (1mM CaCl2 + 1 mM KCl + 1 mM TrisHCl, pH 7.2) and penetrated by microelectrodes was
electrically stimulated, and the electric membrane responses were correlated
with ciliary activity recorded at 250 frames per second. Passive depolarizing deflections of the
membrane potential did not induce ciliary reversal. When depolarizations were large enough to
elicit a regenerative membrane response, a period of reversed ciliary beating
was recorded. With increasing stimulus
intensities the latency of ciliary reversal dropped from 30 to 4 ms, and the duration of reversal of the cilia
increased from 50 ms to 2,4 s or more. The corresponding regenerative response (action potential) was
stimulus-graded in amplitude and rate of rise. Progressively large positive stimulus pulses increased the latency again
and decreased the duration of reversed ciliary beating. 100 ms current pulses shifting the membrane
potential to +70 mV or more suppressed ciliary reversal inducing a brief “off”
response of the cilia at the end of the pulse. The present findings suggest that ciliary reversal is coupled to
membrane depolarization by the influx of Ca2+ across the surface
membrane. Suppression of the ciliary
response during large stimulation occurs when Ca2+ approaches the
equilibrium potential retarding its influx.
15
Properties of polarized ciliary beat in Paramecium.
The spatial properties of the polarized ciliary beat of Paramecium were investigated using a
large-scale wire model of metachronal activity.
The model was constructed in accordance with microscopic surface and
side views of swimming Paramecium
taken by electronic flash photography.
While the metachronal type of the body cilia is dexioplectic, the
2-dimensional views of the cilia in profile are antiplectoidal or symplectoidal
depending on the plane of viewing. Wave length and wave angle can be inferred
from the observed profile views using the wire model of a ciliary field.
14
Temperature influences on ciliary beat and metachronal coordination in Paramecium.
Temperature reduction from 20° to 6°C decreases
ciliary beat frequency with a Q10 of 2,74. The frequency does not
change significantly between 20° and 25°C.
Low temperature particularly reduces the speed of the ciliary effective
stroke, and shifts the dexioplectic metachronal pattern in the counterclockwise
direction. At normal and low temperature
the metachronal wave length of the body cilia exceeds that of the oral groove
cilia.
13
Ciliary activity and the origin of metachrony in Paramecium: Effects of increased viscosity.
Raising the viscosity of the medium beyond 100 cP turns the direction of
the metachronal wave propagation of forward swimming Paramecium progressively clockwise from forward-right to backward
left. At the same time, the direction of
the power stroke is turned clockwise at a lesser rate so that dexioplectic
metachrony transforms to a symplectic pattern, and temporal and spatial
polarization of the ciliary cycle are progressively reduced. The lefthanded swimming helix transforms to a
righthanded helix at viscosities beyond 12 cP.
Ciliary frequency decreases with rising viscosity. The stroboscope reveals a posteriorly
directed gradient of the beating rate.
Raising the viscosity increases the metachronal wave length from 10,7 µm (1 cP) to 14,4 µm (40 cP), whereas the wave velocity
is reduced from 340 to 200 µm/s. A
working hypothesis of viscosity-dependent hydrodynamic coupling of the cilia is
put forward.
12
Verbesserte Schnellfüllung
von Mikrokapillarelektroden.
An improved method of manual backfilling of intracellular microelectrodes
is briefly described.
11
Korrelation zwischen Membranpotential und Fortbewegung bei Stylonychia.
(Correlation between membrane potential and locomotion in Stylonychia
Intracellular recordings of the membrane potential of
the freshwater ciliate Stylonychia
showed a resting potential of -36 to -40 mV (in a solution of 9 mM CaCl2
and 3 mM KCl). Spontaneous spike depolarizations at intervals of one
to five seconds. The spikes are
composed of a peak potential and a shoulder of lesser depolarization lasting up
to several seconds.
10
Primäre und induzierte Bewegungsstadien bei der Osmiumsäurefixierung vorwärtsschwimmender Paramecien.
(Primary and induced states of ciliary function in forward swimming Paramecium using fixation by osmic acid)
A population of Paramecium swimming at 99% in the forward direction was instantaneously fixed using osmic
acid. Among the resulting preparations
of individuals, about 50% showed stages of growing ciliary reversal. The metachronal waves of forward swimming
paramecia were identified in about 40% of the preparations.
9
Regulation der Cilienmetachronie bei der Fluchtreaktion von Paramecium.
(Regulation of ciliary metachronism during the avoidance response of Paramecium)
Paramecia induced to perform high rates of avoiding
reactions by mechanical and chemical stimulation (Ba ions) were instantaneously
fixed with OsO4. Quantitative evaluations of the preparations revealed metachronal stages of transition between the ciliary patterns of backward and forward swimming. In each of the transitory stages, the
metachronal waves of forward swimming were found at the anterior cell end, and
waves of backward swimming were found at the posterior end of the cell. These data confirm the so-called Parducz-scheme of avoiding reaction for the cases of a homogeneous chemical stimulation and mechanical stimulation.
8
Eine 2-Gradientenhypothese für die Metachronieregulation bei Ciliaten.
(A two-gradient hypothesis on the regulation of metachronism in ciliates)
The present hypothesis is based on a re-evaluation of
various wave patterns in ciliates, in particular Paramecium. The phenomena suggest the existence of 2 physiological gradients along the cell membrane, one in the antero-posterior direction, the other extending from the periphery toward the cytostome. Vectorial superposition of these two gradients generates the observed patterns of metachronal wave fronts seen during forward and backward locomotion of the cells.
7
Filmbildanalysen 4 verschiedener Schlagmuster der Marginalcirren von Stylonychia.
(Analysis of four motion patterns of the marginal cirri of Stylonychia)
High-speed cinematography (200 f/s) and single-frame analysis of records of the marginal cirri of Stylonychia mytilus reveals 4 function
types of the cirri: metachrony (slow
phase-shifted beating) without noticeable locomotive effect, heterochrony
(lack of metachronic order but preferred beat direction), achrony (rapid low-amplitude
rotational beating with preferred posteriad or anteriad orientation), synchrony (a single high-amplitude synchronized beat in the anteriad or posteriad direction). Superimposed on these types of functioning
are oscillations of the cirri of minor amplitude. The 4 types of cirral function are correlated with the properties of standstill, forward and backward locomotion of the cell.
6
Zur Koordination und Wirkungsweise der Membranellen von Stylonychia mytilus.
(Coordination and motor effects of the membranelles in Stylonychia mytilus)
The function of the membranellar band of Stylonychia mytilus
was analyzed using high-speed cinematography (200 f/s)
and single-frame analysis. Water currents from ciliary activity were visualized by carmine particles suspended in the medium. In the frontal zone of
the membranellar band the wave length - and thereby wave velocity - decreased
in the proximo-distal direction. During standstill or forward locomotion of the cell, the left portion of the anterior membranellar band beats toward the cytostome, the right portion beats toward the distal end of the row. The border
between these beat directions can be seen to shift. The membranelles do never work in synchrony. However, the membranelles take actively part
in generating backward movement of the cell. Fragments of the membranellar band show the same characteristics as seen
in the entire animal, apart from a smaller beat amplitude and the absence of beat reversal. While the beat direction of membranelles is parallel to the direction of wave transmission, water currents are driven transversally to the membranellar band. As a result, loops of current go
from anterior right to posterior left thereby sweeping food particles to the
cytostome. The generation of transverse water currents is tentatively explained by a turbine-blade effect of the
membranelles.
5
Erschütterungsbedingte Sensibilisierung gegenüber rauhem Untergrund bei Stylonychia mytilus.
(Sensitization to rough surface in Stylonychia mytilus applying vibration)
Responses of Stylonychia mytilus to a rough/smooth chessboard pattern was
examined under various conditions (46 experimental groups, 2303 cells
total). Mechanical stimulation by shaking of the drop volume sensitizes the animals leading to strong avoidance of rough surfaces. Negative sensitization
decreased within 40-60 min. Habituation as a cause for decrease in rough-avoidance was excluded. Feeding with Tetrahymena amplified the intensity and duration of the
avoidance. The individual cell age, daytime, renewal of medium and recording interval had no effect on rough avoidance.
4
Versuche zur Frage nach der Dressierbarkeit hypotricher Ciliaten unter Einsatz hoher Individuenzahlen.
(Conditioning experiments in hypotrich ciliates using large numbers of individual cells)
Conditioning experiments were performed in Stylonychia mytilus (var.I, II, III), Euplotes eurystomus, and Keronopsis rubra
using “rough surface” and “light” as stimuli. Using large numbers of specimens
placed on chess-board patterns, the cells responded differently to “rough
squares” and “smooth squares”. Stylonychia mytilus var. II weakly avoided “rough” during 80 min of exposure. Stylonychia mytilus var. I and III
and Euplotes eurystomus weakly
preferred “rough”. Keronopsis rubra showed a moderate preference of “rough” in tests of 2 and 4 hours. Persistent, strong vibration of the fluid test volume induced an avoidance of “rough” (negative
sensitization). A short-term shaking of up to 1s had no apparent sensitizing effect on Stylonychia. In Stylonychia mytilus var. II and in Keronopsis rubra a very weak but significant avoidance of “light”
(1000 and 160 lux) was demonstrated over periods of 1 and 2 hours. Conditioning of 189 specimens of Stylonychia mytilus var. II over 40 min and 867 specimens of Keronopsis rubra over 2 and 4 hours on chessboard patterns of either stimulus combination (rough-light – smooth-dark; rough-dark – smooth-light) led to negative results: no conditioning could be established. The paper discusses feasibility and limits of “learning” in protozoa.
3
Analyse kurzzeitlicher Bewegungserscheinungen des Ciliaten Stylonychia mytilus Ehrenbg.
(Analysis of short-term motion properties of the ciliate Stylonychia mytilus Ehrenbg)
High resolution electronic flash photographs of Stylonychia mytilus
were used to analyze the patterns of ciliary motility during locomotion. Movements of are classified into 4 fundamental
types (swimming, running, standstill, reversal); these types are characterized
in terms of speed, curvature, and direction of locomotion. “Running” on
substrate surfaces were divided into 3 speed classes (creeping, running I,
running II) and 3 forms of curvature (along with or against body curvature,
straight ahead). Swimming, running, and the rapid reversal movements can occur
in the forward and in the backward direction. The back-and-forth movement (the
so-called “avoiding reaction”) does not occur as a behavioural unit as claimed
by Jennings. It results from a very common junction of 2 reversal movements, which may equally occur in other combinations. Applying various degrees of viscosity of the medium, the marginal cirri show 3 functional types of motility: slow metachrony, rapid metachrony, and synchrony. The locomotive effects can be forward as well as backward. Increase in viscosity (up to 1000 cP)
enhances the distinctness of the motility types. The marginal cirri are highly resistant to raised viscosity. The terminal cirri take part in all functions of the marginal cirri; so do the ventral groups of cirri (frontal, ventral, caudal cirri). The ventral group of cirri establish the “walking movement” of Stylonychia and is therefore not rigidly coupled to the function of the marginal cirri. Metachrony of the membranelles occurs toward the cytostome or away from it; it is largely independent of the working of the cirri. While the cell is at standstill, the marginal cirri perform slow metachrony or they are at total rest. Membranelles are rarely inactivated for a moment. A “running” Stylonychia employs its marginal cirri at “rapid metachrony”. The terminal cirri have a steering function; the same applies to the dragging caudal cirri. During backward locomotion the metachrony of the membranelles is reversed. Swimming cells apply predominantly the rapid metachrony. Reversal movements result from a single synchronous beat of all cirri. The coupling of two mutually reverse synchronous cirral beats generates the back-and-forth movement. The sum of all synchronous cirral beats generates, during cirral reversal, the axial displacement to the right side of the cell. The results on cirral function and coordination in Stylonychia correspond to findings by Parducz (1956a,b) in Paramecium in several respects; the
cirri and membranelles in Stylonychia generate, however, a higher degree of motile sophistication.
2
Abhängigkeit der Lebensdauer und Teilung von Stylonychia mytilus von äußeren Faktoren.
(Dependence of individual lifetime and division of Stylonychia mytilus from external conditions)
The individual behaviour of 392 newly divided Stylonychia mytilus
specimens was investigated as a function of food supply, drop volume, and
temperature. Poor-culture medium (0.06% egg yolk) volumes of 0.05 ml allowed average life times of 10.9 days (30 days maximum). Comparably older individuals
had a higher chance for survival and cell division than younger individuals. Rich culture medium (0.1% yolk) induced high
rates of cell division followed by a depression, which reduced the average and
maximum life duration. With the same condition of food supply, a larger water volume improved the conditions for survival and division. No cell divisions
were observed below 10°C, whereas the individual life span was increased as
compared to controls at room temperature.
1
Analyse langzeitlicher Bewegungserscheinungen des Ciliaten Stylonychia mytilus Ehrenbg.
(Analysis of long-term motion properties of the ciliate Stylonychia mytilus Ehrenbg)
The long-term movements of Stylonychia were analyzed covering periods of 1-1.5 hours (one experiment: 24 hours) applying a new method of recording on magnetic tape. Following cell division locomotive activity
builds up gradually. Running behaviour of various duration and geometric course alternates with standstill or slow creeping movement. Running speed below 0.4mm/s prevails. Maximal speeds of up to 2.5mm/s
are observed. No correlation is found between speed and form of the course. In
general, the intervals of standstill do not exceed 3-4 min. Under conditions of minimal disturbance by external stimuli, motor activity tends to build up gradually. This tendency is superimposed by independent variations in the frequencies in standstill, creeping, running, and back-and-forth movements (“Rückvorbewegungen”). Total locomotor activity tends to be proportional to the frequency of back-and-forth movements. The frequency of pulsating vacuole systoles is very constant; the frequency declines in parallel to a decline of the motor activity. Weak chemical stimulation can induce backward locomotion, in part even backward swimming. The rather
steady occurrence of back-and-forth movements under poor stimulus conditions
suggests that intrinsic factors determine the back-and-forth movement. The term of “avoiding reaction” is justified only for the special case of induction by external stimuli. A periodicity in motor activity, as was previously reported for Paramecium (Dembowski 1924, Rohde 1958), is not found in Stylonychia mytilus.