Effect of direct and transcallosal stimulation on inhibition of unit activity in the cat association cortex

Inhibition of association cortical neurons (in the form of inhibition of spontaneous activity or of IPSPs) during direct and transcallosal stimulation was studied in cats immobilized with muscle relaxants. The duration of inhibition of stimulation and the number of stimuli. With an increase in the strength of stimulation inhibition deepened to a certain level for a particular neuron, after which it could be further lengthened with an increase in the number of stimuli. In the case of repeated stimulation by volleys of stimuli, very prolonged inhibition developed gradually in the neurons, during which spontaneous activity was inhibited for 2–5 sec. The duration of the IPSP depended on the intensity of stimulation and number of stimuli and its amplitude depended on the intensity and frequency of stimulation and on the number of stimuli. In some cases the amplitude of the IPSP continued to rise after a short volley of stimuli, even after the end of stimulation. An increase in the number of stimuli in the volley lengthened the IPSPs, but their amplitude remained constant throughout the period of stimulation. Prolonged inhibition (up to a few seconds) was connected with the development of a hyperpolarization postsynaptic potential in the neurons. It is suggested that neurons exerting a monosynaptic inhibitory influence on cells of the association cortex may be located in the opposite hemisphere.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 13, No. 2, pp. 133–141, March–April, 1981.     

Postsynaptic mechanisms initiating bursting activity in theHelix pomatia RPal neuron under the influence of an interneuron

Postsynaptic mechanisms of the connection between the interneuron in the visceral ganglion initiating bursting activity in RPal and B7 neurons and these neurons themselves were investigated in the snail (Helix pomatia). Using voltage clamping at the membrane of these cells, stimulation of the interneuron gave rise to a slow inward current with a 2 sec latency; it rose in amplitude as stimulation increased in duration. Reducing the temperature from 25 to 5°C diminished the rise and decay rate of this current with a temperature coefficient of about 10. The current-voltage relationship of the slow inward current was nonlinear, with a maximum of –65 mV. Reducing the concentration of sodium ions in the extracellular fluid increased the amplitude of the current. While hyperpolarization of the burster neuron membrane produced a burst of inward current prior to stimulation, this same hyperpolarization induced a pulse of outward current at the peak of the slow inward current. Stimulating the interneuron is thus thought to activate at least two types of ionic channel in the cell body of the burster neurons: a steady sodium and a voltage- and time-dependent channel for outward current. This process could well be mediated by a biochemical cytoplasmic chain reaction.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 19, No. 1, pp. 28–36, January–February, 1987.     

Effect of intracellular injection of cyclic amp on electrical characteristics of identified neurons in Helix pomatia

The effect of intracellular iontophoretic injection of cyclic AMP on electrical activity of neurons RPa1, RPa3, LPa2, LPa3, and LPl1 in the corresponding ganglia ofHelix pomatia was investigated. Injection of cyclic AMP into neuron LPl1 was found to cause the appearance of rhythmic activity (if the neuron was originally "silent"), an increase in the frequency of spike generation (if the neuron had rhythmic activity), and a decrease in amplitude of waves of membrane potential, in the duration of the interval between bursts, and in the number of action potentials in the burst (if the neuron demonstrated bursting activity). In the remaining "silent" neurons injection of cyclic AMP led to membrane depolarization. Injection of cyclic AMP into neurons whose membrane potential was clamped at the resting potential level evoked the development of an inward transmembrane current (cyclic AMP current), the rate of rise and duration of which increased proportionally to the size and duration of the injection. Theophylline in a concentration of 1 mM led to an increase in the amplitude and duration of the cyclic AMP current by about 50%. It is concluded that a change in the cyclic AMP concentration within the nerve cell may modify the ionic permeability of its membrane and, correspondingly, its electrical activity.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 12, No. 5, pp. 517–525, September–October, 1980.     

Postsynaptic inhibition in the primordial hippocampus of the frog

Postsynaptic responses of neurons of the primordial hippocampus to electrical stimulation of brain structures belonging to the visual and olfactory afferent systems were investigated in frogs (Rana temporaria) immobilized with diplacin. * Short-latency (early) and long-latency (late) IPSPs evoked by both olfactory and visual afferent inputs, most probably activated by different conducting systems, are described. Impulses of different modalities can induce both similar and different IPSPs in a neuron. The conducting systems may have a common interneuron for the visual input and specific interneurons for the olfactory input. IPSPs evoked by visual impulses were similar in location to the early IPSP of the olfactory afferent input. Convergence of the systems of early and late inhibition on one neuron was frequently observed for the olfactory afferent input.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 5, No. 6, pp. 583–592, November–December, 1973.     

Synaptic mechanisms controlling receptor unit activity in the stretch receptor—Abdominal ganglionic chain system of the crayfish

Inhibitory control over activity of the receptor neuron was investigated in a preparation of the stretch receptor and abdominal ganglionic chain in crayfishes. Potentials were recorded intracellularly from receptor neurons and neurons of the abdominal ganglion, and extracellularly from the dorsal roots. IPSPs appeared in the receptor neuron in response to stimulation of that same neuron or of the abdominal ganglionic chain. The relationship between spikes at the input and output of the inhibitory neuron varied over a wide range depending on the functional state of the neuron. A linear relationship was established between the time before appearance of the IPSP and the duration of the interspike interval of the slowly adapting neuron (SAN) and also between the firing rate of this and the inhibitory neurons during recurrent inhibition. Factors influencing the length of the interspike interval of the SAN on the appearance of an IPSP in it were investigated. It is postulated that summation of potentials evoked by spikes of the SAN and also of potentials evoked by spikes of that neuron, together with local processes evidently of endogenous nature takes place in the inhibitory neuron. IPSPs were recorded from two neurons resistant to strychnine and blocked by picrotoxin on the receptor neuron. The structural and functional organization of the individual elements in the chain of recurrent inhibition and inhibition evoked by stimulation of the abdominal ganglionic chain is discussed.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 5, No. 3, pp. 323–332, May–June, 1973.     

Postinhibitory unit response of crustacean stretch receptors after direct and recurrent inhibition

The postinhibitory response of a slowly adapting neuron was investigated in experiments on an isolated preparation of crustacean stretch receptor and abdominal nerve chain. The structural features of this preparation are such that this response can be regarded as the response of the postsynaptic membrane to synaptic inhibition and not the action of synaptic excitation. IPSPs arise in the slowly adapting neuron in response to stimulation of the abdominal nerve chain (direct inhibition) or to excitation of the neuron itself (recurrent inhibition). The postinhibitory response consists of the development of action potentials or an increase in their amplitude and frequency. The magnitude of the response is determined by the duration of the inhibition and the state of the neuron membrane. The postinhibitory response was strongest when IPSPs were superposed on cathodal depression. IPSPs and an intracellular hyperpolarizing current evoke similar postinhibitory responses. Repetitive excitation of an inhibitory neuron may result in the appearance of a regular spike discharge from a previously inactive neuron through the mechanism of the postinhibitory response. Activation of a chain of recurrent inhibition increases the duration of the postinhibitory response evoked by direct inhibition or by a hyperpolarizing current. The existence of a chain of recurrent inhibition prevents the cessation of firing by a neuron during increasing cathodal depression. A mechanism of postinhibitory rebound lies at the basis of this phenomenon.     

Ionic mechanisms of the transmembrane current evoked by injection of cyclic amp into identified Helix pomatia neurons

Ionic mechanisms of the transmembrane current evoked by injection of cyclic AMP into identified neurons ofHelix pomatia were investigated by the voltage clamp method. Injection of cyclic AMP into neurons RPa3, LPa2, LPa3, and LPl1 was shown to cause the development of a two-component transmembrane (cyclic AMP) current. The current-voltage characteristic curve of the early component is linear in the region from –40 to –90 mV; the reversal potential of the early component, determined by extrapolation, lies between –5 and +20 mV; the current-voltage characteristic curve of the late component also is linear and has a reversal potential between –55 and –60 mV. A decrease in the sodium concentration in the external medium from 100 to 25 mM led to a decrease in amplitude of the cyclic AMP current and to a shift of the reversal potential for the early component by 30–32 mV toward hyperpolarization. It is suggested that the early component of the cyclic AMP current in neurons RPa3, LPa2, LPa3, and LPl1 is associated with an increase in permeability of the neuron membrane chiefly for sodium ions, whereas the late component is correspondingly connected with permeability for potassium ions. Injection of cyclic AMP also caused the appearance of a transmembrane inward current in neuron LPa8, but it was independent of the holding potential and was unaccompanied by any change in membrane permeability. It is suggested that this current may be due to a change in the activity of the electrogenic ion pump.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 12, No. 5, pp. 526–532, September–October, 1980.     

Effect of pentobarbital on neuronal inhibitory response evoked in an isolated slab of cat auditory cortex by intracortical stimulation

Neuronal responses of an acutely isolated slab of auditory cortex (area AI) to intracortical electrical stimulation were studied intracellularly in cats anesthetized with pentobarbital. It was found that 77% of responses were primary IPSPs, and allowing for secondary inhibitory responses, an inhibitory response was observed in 92% of neurons. All types of neuronal responses in the slab were short-latency. The maximal response latency did not exceed 5 msec. Neurons responding to stimulation by IPSPs were found at all depths in the slab, with a maximum in layers II–III. Nearly all primary IPSPswere mono- and disynaptic. Pentobarbital increased the duration of individual neuronal inhibitory responses in the isolated slab of auditory cortex without affecting maximal duration of the IPSP. The mechanisms of the effect of pentobarbital on the amplitude and duration of IPSPs are discussed.I. I. Mechnikov Odessa State University. Translated from Neirofiziologiya, Vol. 16, No. 2, pp. 147–152, March–April, 1984.     

Inhibitory synaptic potentials of the smooth muscle cells of guinea pig taenia coli

A single submaximal intramural application of rectangular stimuli (duration 0.2–0.5 msec) to an atropine-treated taenia coli muscle band evoked inhibitory postsynaptic potentials (IPSP) and a marked relaxation of the muscle band in the vast majority of muscle cells. The latency period of the IPSP was 122±16 msec; the times for a rise and fall of amplitude were 96±8 and 370±60 msec, respectively. The mean latency period of muscle relaxation was 800 msec. The latency period, and especially the amplitude of the IPSP depended on the intensity of the intramural stimulation. This indicates that one muscle cell is inhibited by several nerve fibers. IPSP evoked by threshold stimuli displayed a tendency toward summation, while the amplitude of the second and of subsequent IPSP evoked by low-frequency maximal stimuli was always less than that of the first IPSP. After periodic stimulation (frequency 10–60 impulses/min) was discontinued, a posttetanic decrease in IPSP amplitude was observed. Anodic polarization of the muscle band with a direct current raised the effectiveness of synaptic transmission, as was evidenced by the considerable increase in IPSP amplitude. When the muscle membrane was hyperpolarized with noradrenaline, IPSP inhibition was reversible. This is evidence that the unknown mediator and noradrenaline have a common ionic inhibitory mechanism.A. A. Bogomol'ts Institute of Physiology of the Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 2, No. 5, pp. 544–551, September–October, 1970.     

Origin of slow negative potential of direct cortical response in cats

To investigate mechanisms of formation of the electrocorticographic slow negative potential (SNP) evoked by direct electrical stimulation of the cortical surface, poststimulus single unit activity in the stimulated area was studied in anesthetized cats and changes in SNP in the depth of the cortex were analyzed. The results showed that membrane hyperpolarization, accompanied by cessation of action potential generation, develops parallel with SNP in neuron bodies in the stimulated area. Investigation of the nature of this hyperpolarization showed that during its development excitability of the neuron and resistance of the postsynaptic membrane fall. It is concluded from the results that this membrane hyperpolarization is an indicator of IPSP development in the neuron bodies. The results of laminar recording showed that SNP may diminish or even disappear in the depth of the cortex without subsequent reversal. Determination of dipoles formed along an axis perpendicular to the cortical surface showed that SNP has one source and two sinks, which are located symmetrically relative to it. The presence of two symmetrical sinks must indicate an active source, formed as a result of hyperpolarization of the neuron membrane. On the basis of the results SNP can be regarded as a field potential formed on the cortical surface as a result of IPSP development in the neuron bodies.Institute of Clinical and Experimental Neurology, Ministry of Health of the Georgian SSR, Tbilisi. Translated from Neirofiziologiya, Vol. 15, No. 3, pp. 314–320, May–June, 1983.     

Postsynaptic potentials of neurons of the cat auditory cortex

The electrical reactions of 294 neurons of the auditory cortex to a click were recorded in experiments on cats immobilized with tubocurarine (174 intra- and 120 extracellularly). The value of the membrane potential varied from 30 to 70 mV with intracellular leads. The following types of reactions were obtained (the number of neurons is given in parentheses): a peak without slow oscillations in the membrane potential (4), EPSP (3), EPSP-peak (6), EPSP-peak-IPSP (17), EPSP-IPSP (9), primary IPSP (114, including 23 with an after-discharge). Twenty one neurons did not react to a click. The amplitude of the sub-threshold EPSP was 1–1.5 mV, the duration of the ascending part was about 10 and of the descending part 20–30 msec. The peak potential on the ascending part of the EPSP developed at the critical level of 3–4 mV. The amplitude of the peaks varied from several millivolts to 50–60. In 17 neurons prolonged hyperpolarization having all the properties of an IPSP, developed after the peak. The amplitude of these IPSP varied in different neurons from 1 to 10 mV and the duration varied from 20 to 80 msec. IPSP without preceding excitation of the given neuron were the predominant types of reaction. The latent period of these primary IPSP varied from 7 to 20 msec and the amplitude from 1 to 15 msec with a duration of 30–200, more frequently 80–100 msec. It is suggested that two types of inhibition develop in neurons of the auditory cortex in response to a click: recurrent and afferent. The functional significance of the first consists in limiting the duration of the discharge in the reacting neurons, the second prevents the development of excitation in adjacent neurons, thereby limiting the area of neuronal activity.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSSR, Kiev. Translated from Neirofiziologiya, Vol. 3, No. 4, pp. 339–349, July–August, 1971.     

Investigations of the ionic mechanisms of bursting activity in Helix pomatia neurons

Steady-state current-voltage characteristics of the membrane and ionic currents arising during changes in membrane potential in bursting neurons ofHelix pomatia were studied by the voltage clamp method. The steady-state current-voltage characteristics of the membrane were shown to have a nonlinear region. Replacement of sodium ions by Tris-HC1 ions in the external solution completely abolishes this nonlinearity. Hyperpolarization of the membrane under voltage clamp conditions leads to the development of an outward current which reaches a maximum and then is inactivated. This current has a reversal potential in the region of the potassium equilibrium potential. Depolarization of the membrane to the threshold value for excitation of uncontrollable regions of the axon hillock causes the appearance of a slow inward current. After reaching a maximum, the inward current falls to zero. A model of generation of waves in a bursting neuron is suggested.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 10, No. 2, pp. 193–202, March–April, 1978.     

Inhibition in hippocampal pyramidal neurons during peripheral stimulation

Responses of hippocampal pyramidal neurons were investigated intracellularly in unanesthetized rabbits immobilized with tubocurarine. A single stimulus, applied to the sciatic nerve, evoked prolonged (up to 2.5 sec) hyperpolarization of the cell membrane, accompanied by inhibition of action potentials. The latent period of the evoked hyperpolarization was 48±16.4 msec, and its amplitude 2.5±1.9 mV. In some neurons the development of hyperpolarization potentials was preceded by excitation. The suggestion is made that hyperpolarization of the membrane of pyramidal cells during peripheral stimulation is manifested as an inhibitory postsynaptic potential (IPSP), generated with the participation of hippocampal interneurons. The possibility of prolonged tonic action of interneurons from outside as a cause of prolonged inhibition of the pyramidal neurons is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 1, No. 3, pp. 278–284, November–December, 1969.     

Synaptic events during specific and nonspecific inhibition of visual cortical neurons

Intracellular and quasi-intracellular recordings were made of changes in membrane potential in visual cortical neurons of the waking rabbit during specific (to flashes) and nonspecific (to nonvisual stimuli) inhibition. As a rule, specific inhibition was accompanied by some degree of hyperpolarization of the cell membrane while nonspecific was unaccompanied by any appreciable degree of membrane hyperpolarization. It is postulated that this difference is caused by differences in the arrangement of the inhibitory synapses on the body and dendrites of the neurons. Long-latency prolonged IPSPs arising in response to photic stimulation can be suppressed by the action of various nonvisual stimuli and by stimulation of the mesencephalic reticular formation. A decrease in amplitude of the IPSPs may lead to filling of the inhibitory pauses with spikes. These phenomena are evidently based either on inhibition of inhibitory neurons or on a disturbance of the synchronization of their discharges, leading to weakening of the integral IPSPs.Brain Institute, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 4, No. 4, pp. 349–357, July–August, 1972.     

Peculiarities of orthodromic inhibition in pacemaker neurons in Helix pomatia

We used the intracellular recording method to study the effect of a group of nerves in the visceral complex on the activity of a pacemaking giantneuron located in the peripheral part of the visceral ganglion in a mollusk. Single excitations of the left and right pallial, the intestinal, and the anal nerves with electrical stimuli evoked similar responses, consisting of phases of rapid depolarization (duration 100 msec, amplitude 3–5 mV) and slower hyperpolarization (duration 400 msec, amplitude 5–8 mV). The excitation also had an aftereffect, which was expressed in inhibition of the background activity of the pacemaker for several seconds. The most interesting of the functional characteristics of that response was the effects of summation. With rhythmic excitation by stimuli of low frequency (0.5–1 c/sec) the result of summation was general hyperpolarization of the neuron and the appearance of giant inhibitory postsynaptic potentials (IPSP's) with an amplitude of 12–16 mV. With higher frequency of excitation (2–3 c/sec and upward) we observed depolarization replacing the hyperpolarization of the neuron, but IPSP's of large amplitude were absent. At the end of rhythmic excitation prolonged inhibition of the pacemaker's activity, lasting some minutes, occurred in all cases. This article discusses the possible mechanisms of that type of prolonged inhibition of the pacemaker's activity, the origin of the phases in biphasic responses, and the reasons for differences in the course of summation of biphasic postsynaptic potentials.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 3, No. 4, pp. 426–433, July–August, 1971.     

Inhibitory effects of reticulospinal fibers of the lateral funiculus on neurons of thoracic spinal reflex pathways

Experiments on anesthetized cats with partial transection of the spinal cord showed that reticulo-spinal fibers in the ventral part of the lateral funiculus participate in the inhibition of polysynaptic reflexes evoked by stimulation of the ipsi- and contralateral reticular formation. The reticulo-fugal wave in the ventrolateral funiculus evoked comparatively short (up to 70 msec) IPSPs in some motoneurons of the internal intercostal nerve investigated and at the same time evoked prolonged (up to 500 msec) inhibition of IPSPs caused by activation of high-threshold segmental afferents. This wave also led to the appearance of IPSPs in 14 of 91 (15.5 %) thoracic spinal interneurons studied. The duration of these IPSPs did not exceed 100 msec; meanwhile, segment excitatory responses of 21 of 43 interneurons remained partly suppressed for 120–500 msec. It is concluded that the inhibitory action of the lateral reticulo-spinal system on segmental reflexes is due to several synaptic mechanisms, some of them unconnected with hyperpolarization of spinal neurons. The possible types of mechanisms of this inhibition are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 10, No. 2, pp. 162–172, March–April, 1978.     

Inhibitory Synapses on Pacemaker Neurons in the Heart Ganglion of a Stomatopod, Squilla oratoria

The pacemaker neurons of the Squilla heart ganglion are innervated from the CNS through three pairs of extrinsic nerves. One of them, the α-nerve, is inhibitory to the heart beat. The effect of α-nerve stimulation on the pacemaker potential was examined with intracellular electrodes. Without extrinsic nerve stimulation the membrane potential of the pacemaker cell fluctuated spontaneously. On application of a tetanic train of stimuli to the α-nerve the membrane potential was shifted and fixed to a steady level, which with K₂SO₄-filled electrodes was near the peak of hyperpolarization after a spontaneous burst, but was less negative with KCl-filled electrodes. The shift of the membrane potential was due to the summated IPSP's. By changing the level of the membrane potential with injection of the polarizing current the IPSP could be reversed in sign, and the size of the IPSP was linearly correlated with the membrane potential level. During inhibition the membrane conductance increased. The increase depended on divalent cation concentrations in the outside medium. In Ca-rich saline the IPSP was greatly enhanced. In Mg-rich saline it was suppressed. The amplitude of antidromic spikes was reduced during inhibition especially when the spike frequency was high.     

Intracellular responses of primary auditory cortical neurons to tones of different frequencies and to electrical stimulation of spiral ganglion fibers in cat

Experiments on cats anesthetized with pentobarbital showed that, depending on the intensity and frequency of acoustic stimulation, neurons in auditory area AI give responses of EPSP, EPSP-spike-IPSP, EPSP-IPSP, and IPSP type. Presentation of a tone of characteristic or near-characteristic frequency and above-threshold intensity, and also electrical stimulation of nerve fibers of the spiral ganglion, innervating the central zone of the receptive field of the neuron, evoke in most cases a response of EPSP-spike-IPSP type. Tone differing considerably in frequency from the characteristic, and electrical stimulation of peripheral zones of the receptive field, evoked responses of EPSP-IPSP or IPSP type. The range of frequencies of tones to which, at threshold intensity, an action potential is generated by the neuron is considerably narrower than the range of frequencies of tones evoking an EPSP and IPSP. Above the intensity of tone threshold IPSP is an invariable component of the response of most neurons in area AI. The appearance of an IPSP in the neuron is accompanied by depression of spontaneous activity and the neuronal response to testing stimulation. Two types of IPSP were distinguished: One type is a component of the EPSP-spike-IPSP response and arises during excitation of auditory receptors located in the central part of the receptive field of the neuron, the other arises during excitation of receptors located at the periphery of the field, and which project to neurons with other characteristic frequencies. The former arise after spike excitation of the neuron, the latter after EPSP or primarily.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 16, No. 1, pp. 123–131, January–February, 1984.     

Effect of high intracellular calcium ion concentration on the transmembrane current induced by iontophoretic injection of cAMP inHelix pomatia neurons

The effect of increasing the intracellular calcium ion concentration by various methods (iontophoretic injection into the cytoplasm, generation of a burst of action potentials, addition of uncouplers of oxidative phosphorylation to the external solution, causing release of calcium from mitochondria) on the inward current induced by injection of cAMP into the neuron (the cAMP current) was investigated on the neuron membrane ofHelix pomatia under voltage clamp conditions. In all cases an increase in the intracellular calcium ion concentration was found to lead to an increase in amplitude, and in many cases duration, of the cAMP current. It is suggested that membrane structures responsible for appearance of the cAMP current have two phosphorylation centers: cAMP-dependent and calcium-calmodulin-dependent. The possible role of this process in signal integration at the intraneuronal level is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 17, No. 1, pp. 78–84, January–February, 1985.     

Hyperpolarization-activated inward current associated with the frequency increase in ciliary beating of Paramecium

Summary In order to study the relationship between the inward Ca current activated by hyperpolarization and the frequency increase in ciliary beating, Paramecium cells were voltage clamped under conditions where K current was suppressed by use of CsCl electrodes and by extracellular tetraethyl ammonium. A 2-s pulse of hyperpolarization from the resting potential activated an inward current consisting of two components, an initial transient current peaking at 0.1–0.2 s (which had been identified as a Ca current) and a subsequent sustained current. The initial component was not associated with the frequency increase because the frequency increase was normally induced even when the peak current was almost completely inhibited by external addition of Ba²⁺. The second sustained current was closely correlated with the frequency increase. The frequency rose steeply with the sustained current and saturated at –0.6 nA. External addition of La³⁺ or replacement of Ca²⁺ by Mg²⁺ suppressed this current, and at the same time the frequency increase was inhibited. As the amplitude of the sustained current was not changed by deciliation, this current must pass through the somatic membrane. These results suggest that the frequency increase upon hyperpolarization is triggered by the voltage-activated inward current passing through the somatic membrane of the interciliary compartment.Abbreviations cAMP cyclic adenosine monophosphate - HEPES hydroxyethylpiperazine ethanesulfonate - TEA⁺ tetraethyl ammonium