Effects of external ions on membrane potentials of a lobster giant axon

The effects of varying external concentrations of normally occurring cations on membrane potentials in the lobster giant axon have been studied and compared with data presently available from the squid giant axon. A decrease in the external concentration of sodium ions causes a reversible reduction in the amplitude of the action potential and its rate of rise. No effect on the resting potential was detected. The changes are of the same order of magnitude, but greater than would be predicted for an ideal sodium electrode. Increase in external potassium causes a decrease in resting potential, and a decrease in potassium causes an increase in potential. The data so obtained are similar to those which have been reported for the squid giant axon, and cannot be exactly fitted to the Goldman constant field equation. Lowering external calcium below 25 mM causes a reduction in resting and action potentials, and the occasional occurrence of repetitive activity. The decrease in action potential is not solely attributable to a decrease in resting potential. Increase of external calcium from 25 to 50 mM causes no change in transmembrane potentials. Variations of external magnesium concentration between zero and 50 mM had no measurable effect on membrane potentials. These studies on membrane potentials do not indicate a clear choice between the use of sea water and Cole's perfusion solution as the better external medium for studies on lobster nerve.     

Electrical characteristics of ascidian egg fragments

Fragments of ascidian eggs, but at random in any plane and ranging in size from 10 to 90% of the total egg volume, displayed the electrical characteristics of the intact egg, having a resting potential of -86 mV and giving rise to an action potential upon stimulation by electrical current injection. Following insemination, the fragments generated fertilization potentials, comparable to those of intact eggs, although the repolarization phase was shorter. Our data show that there are sufficient ion channels throughout the egg surface to generate action potentials and fertilization potentials in excised egg fragments, irrespective of their global origin. Furthermore, the fertilizing spermatozoon is capable of activating fertilization channels in areas of the egg plasma membrane not destined for sperm entry.     

Intercellular communications within the rat anterior pituitary XII: immunohistochemical and physiological evidences for the gap junctional coupling of the folliculo-stellate cells in the rat anterior pituitary

Since Farquhar [1957. "Corticotrophs" of the rat adenohypophysis as revealed by electron microscopy. Anat. Rec. 127, 291] was the first to report the presence of agranular folliculo-stellate cells as corticotrophs in the anterior pituitary gland, there were no reports about electro-physiological characteristics of the folliculo-stellate cells because of its no hormonal activity and the chaotic distribution of the parenchyma cells. Male Wistar rats, aged 7 weeks with weighing 250--300 g, were separated into two groups. One group was used for immunohistochemical and light microscopical studies to detect S-100 protein and connexin 43. The other group was used for the electro-physiological study and then for the electron microscopical study to know the fine structural character of folliculo-stellate cells after the electro-physiological experiment. Clusters of S-100 protein cells (agranulated folliculo-stellate cells) and numerous connexin 43 positive sites on S-100 protein cells were clear in the "transitional zone" at which the pituitary tissue made the transition from the pars tuberalis to the proximal part of the anterior lobe. Penetration of electrodes to the cells distributed in the transitional zone showed stable membrane potential ranged between--27 and--67mV with no spontaneous activity. Random penetration of electrode showed that larger populations of cell ( approximately 80%) had membrane potentials with -55.6+/-5.1 mV, and less than 20% of cells had the resting membrane potential with -36.0+/-4.4 mV. There were two types of cell couplings; one major group for the recordings from cells with similar deep resting membrane potentials and the other for the recordings from cells with different resting membrane potentials. The former indicated that two cells were electrically coupled while the latter no electrical couples were observed. Carbenoxolone depolarized the membrane by 12.3+/-5.5 mV and reduced the amplitude of electrotonic potentials, and the response recovered by removal of carbenoxolone by the superfusate. The transitional zones of the pituitary glands examined the electrical coupling were observed by an electron microscopy. Almost cytological profiles were observed as intact. The results clearly indicated that the folliculo-stellate cell system deeply participated in the regulation of the anterior pituitary parallel with the portal vessel system, which was the main regulatory system for pituitary hormone secretion.     

Action Potential in the Trap-lobes of Aldrovanda vesiculosa

The trap of Aldrovanda vesiculosa, an aquatic insectivorousplant, consists of a pair of lobes (trap-lobes) which bordereach other at the midrib. The central portion of the lobe iscomposed of three cell layers, an inner and outer epidermisenclosing a single middle layer of relatively large cells, whereasthe marginal portion consists only of the two epidermal celllayers. Intracellular potentials of these cells were measuredby the microelectrode technique. All the cells of the lobeswere excitable and had identical membrane potentials at rest( –110 mV) and during action (amplitude, 130 mV). Theaction potential of each cell was elicited by bending a sensoryhair, one of many standing on the inner surface of the centralportion, or by injecting an outward current into another cellin the lobe. Action potentials were propagated throughout thetrap-lobes at a rate of about 8 cm/sec. The maximum rising ratewas 2.7 V/sec and the duration of the action potential was 1sec. (Received August 8, 1981; Accepted October 15, 1981)     

Single chloride-selective channels active at resting membrane potentials in cultured rat skeletal muscle.

The patch-clamp technique was used to characterize channels that could contribute to the resting Cl-conductance in the surface membrane of cultured rat skeletal muscle. Two Cl- -selective channels, in addition to the Cl- -selective channel of large conductance described previously (Blatz and Magleby, 1983), were observed. One of these channels had fast kinetics and a conductance of 45 +/- 1.8 pS (SE) in symmetrical 100 mM KCl. The other had slow kinetics and a conductance of 61 +/- 2.4 pS. The channel with fast kinetics typically closed within 1 ms after opening and flickered between the open and shut states. The channel with slow kinetics typically closed within 10 ms after opening and displayed less flickering. Both channels were active in excised patches of membrane held at potentials similar to resting membrane potentials in intact cells, and both were open a greater percentage of time with depolarization. Under conditions of high ion concentrations, both channels exhibited nonideal selectivity for Cl- over K+ with the permeability ratio PK/PCl of 0.15-0.2. Additional experiments on the fast Cl- channel indicated that its activity decreased with lowered pHi and that SO2-4 and CH3SO-4 were ineffective charge carriers. These findings, plus the observation that the fast Cl- channel was also active in membrane patches on intact cells, suggest that the fast Cl- channel provides a molecular basis for at least some of the resting Cl- conductance. The extent to which the slow Cl- channel contributes is less clear as it was typically active only after excised patches of membrane had been exposed to high concentrations of KCl at the inner membrane surface.     

Electrophysiological studies of the protozoan,Stentor coeruleus

Transmembrane potentials and membrane characteristics of Stentor coeruleus were studied by means of microelectrodes and standard electrophysiological techniques. Intracellular resting potentials were found to be variable and recordable for only a brief span of time owing to the encapsulation of the recording electrodes. During this brief time span of recorded resting potentials were anamolous in that they were generally of positive polarity. When an extended Stentor was stimulated to contract, a 10–60 mv negative-going transient response was recorded from intracellular electrodes. After the electrodes had been encapsulated, a diphasic transient response was observed when the penetrated animal contracted. Simultaneous recordings from intracellular and encapsulated electrodes showed that the diphasic and negative-going transient responses occurred simultaneously. Contractions of Stentor occurred in 7 to 8 msec following a 2 to 3 msec latent period after a suprathreshold shock. Records obtained by use of photomultiplier and microelectrodes indicated that the contractions began 1.8 msec after the onset of the diphasic response. Prepotentials were observed prior to mechanically stimulated responses.     

Effects of external ions on membrane potentials of a crayfish giant axon

Transmembrane potentials in the crayfish giant axon have been investigated as a function of the concentration of normally occurring external cations. Results have been compared with data already available for the lobster and squid giant axons. The magnitude of the action potential was shown to be a linear function of the log of the external sodium concentration, as would be predicted for an ideal sodium electrode. The resting potential is an inverse function of the external potassium concentration, but behaves as an ideal potassium electrode only at the higher external concentrations of potassium. Decrease in external calcium results in a decrease in both resting potential and action potential; an increase in external calcium above normal has no effect on magnitude of transmembrane potentials. Magnesium can partially substitute for calcium in the maintenance of normal action potential magnitude, but appears to have very little effect on resting potential. All ionic effects studied are completely reversible. The results are in generally good agreement with data presently available for the lobster giant axon and for the squid giant axon.     

Origins of the transient anterior-posterior asymmetry in the frog lens fiber potential

The origin of the transient asymmetry of intracellular resting potentials between the anterior and posterior lens fibers was investigated in the isolated American bullfrog lens by a conventional microelectrode technique. In high K+, Rb+, Cs+, or NH+4 test solution applied only to the lens anterior or posterior side, anterior fibers depolarized at a slower rate than posterior ones. After a long exposure, however, the transient potential difference disappeared. The magnitude of the depolarizations of the lens fibers was in the order of K+ greater than Rb+ greater than Cs+ greater than NH+4. The resting potentials plotted as a function of external K+ concentrations ([K]0) were in agreement with Nernst equation predictions with a slope of 58 mV/decade ion concentration change. A small Na+ permeability is unmasked at a [K]0 less than 10 mM. It was concluded that the transient difference measured in potentials of anterior and posterior lens fibers on increasing external K+, Rb+, Cs+ or NH+4 depends on the anterior epithelial cell layer, which is a diffusional barrier for ions penetrating into the lens interior.     

Effects of different ions on resting polarization and on the mass receptor potential of carotid body chemosensors

The carotid body and its own nerve were removed from cats anesthetized with sodium pentobarbital and placed in an air gap system; the carotid body was bathed in modified Locke's solution equilibrated with 50% O₂ in N₂, pH 7.43 at 35°C. The sensory discharges, changes in “resting” receptor polarization and the mass receptor potential evoked by ACh or NaCN were recorded with nonpolarizable electrodes placed across the gap. Receptor potentials and sensory discharges evoked by ACh showed an appreciable increase in amplitude and frequency when the preparation was bathed in eserinized Locke. Eserine did not change appreciably the responses evoked by NaCN. Excessive depolarization elicited by either ACh or NaCN was accompanied by sensory discharge block. Removal of K⁺ ions from the bathing solution induced receptor hyperpolarization and an increase in the amplitude of the evoked receptor potentials. An increase of K⁺ concentration had the opposite effect. Reduction of Na⁺ or NaCl to one half, or total removal of this salt, induced an initial reduction and later disappearance of the sensory discharges, some receptor hyperpolarization and a reduction in the amplitude of the evoked receptor potentials. Reduction or removal of Ca⁺⁺ produced receptor depolarization, a marked depression of the evoked receptor potentials, an increase in the frequency of the sensory discharges and a reduction in the amplitude of the nerve action potentials. High Ca⁺⁺ or Mg⁺⁺ had little or no effect on action potential amplitude or resting polarization, but decreased sensory discharge frequency and the evoked receptor potentials. Total or partial replacement of Ca⁺⁺ with Mg⁺⁺ induced complex effects: (1) receptor depolarization which occurred in low Ca⁺⁺, was prevented by addition of Mg⁺⁺ ions; (2) the amplitude of the evoked receptor potentials was depressed; (3) the nerve discharge frequency was reduced as it was in high Mg⁺⁺ solutions; and (4) the amplitude of the nerve action potentials was reduced as it was in low Ca⁺⁺ solutions. Temperature had a marked effect on the chemoreceptors since a t high temperatures the receptors were depolarized and the discharge frequency increased. The baseline discharge and responses evoked by ACh or NaCN were depressed at low temperatures. The results are discussed in terms of possible receptor mechanisms influenced by the different ions.     

Osmotic stimuli induce epithelial-dependent relaxation in the guinea pig trachea

Epithelium in airways, like endothelium in blood vessels, may regulate responses of adjacent smooth muscle. To study the intact trachea from guinea pigs we developed an in vitro preparation that permits independent stimulation from either the inner epithelial surface or the outer serosal surface. The whole guinea pig trachea was excised, cannulated, and perfused at a constant flow with Krebs-Henseleit (KH) solution that was in direct contact with the inner epithelial-lined surface. The outer serosal surface of the trachea was immersed in a separate system (bath) containing KH solution. Tracheal responses were assessed by measuring the pressure drop between the tracheal inlet and the outlet under conditions of constant flow. When the trachea was precontracted with carbachol or KCl, hyperosmolar stimuli (KCl, mannitol, urea, or NaCl) produced concentration-dependent relaxation when applied to the inner epithelial surface. Relaxation was not produced when the hyperosmolar stimulus was applied to the serosal surface and was markedly reduced or abolished when the epithelial surface had been physically damaged or removed. These results indicate that hyperosmotic stimuli induce epithelial-dependent relaxation of trachea. A defect in this mechanism may be partially responsible for the bronchoconstriction seen in asthmatic subjects after exercise.     

Membrane Potentials of the Lobster Giant Axon Obtained by Use of the Sucrose-Gap Technique

A method similar to the sucrose-gap technique introduced be Stäpfli is described for measuring membrane potential and current in singly lobster giant axons (diameter about 100 micra). The isotonic sucrose solution used to perfuse the gaps raises the external leakage resistance so that the recorded potential is only about 5 per cent less than the actual membrane potential. However, the resting potential of an axon in the sucrose-gap arrangement is increased 20 to 60 mv over that recorded by a conventional micropipette electrode when the entire axon is bathed in sea water. A complete explanation for this effect has not been discovered. The relation between resting potential and external potassium and sodium ion concentrations shows that potassium carries most of the current in a depolarized axon in the sucrose-gap arrangement, but that near the resting potential other ions make significant contributions. Lowering the external chloride concentration decreases the resting potential. Varying the concentration of the sucrose solution has little effect. A study of the impedance changes associated with the action potential shows that the membrane resistance decreases to a minimum at the peak of the spike and returns to near its initial value before repolarization is complete (a normal lobster giant axon action potential does not have an undershoot). Action potentials recorded simultaneously by the sucrose-gap technique and by micropipette electrodes are practically superposable.     

Electrophysiological recordings from spontaneously contracting reaggregates of cultured vascular smooth muscle cells from chick embryos

Single cells were trypsin-dispersed from blood vessels (great vessels near the heart and mesenteric vessels) of 10–20 day chick embryos, and induced to reaggregate into small spheres (0.1–0.5 mm ) either by gyration or by plating on cellophane. Many reaggregates contracted spontaneously or in response to electrical stimulation during culture periods of up to 6 weeks. When the spherical reaggregates were allowed to adhere to a glass substrate, cells emigrated from the spheres to form aprons of monolayered cells which continued to contract. Thick and thin myofilaments (mean diameters of 146 and 65 Å, respectively) were observable in a large fraction of cells studied in electron micrographs. Vascular smooth muscle (VSM) cells were identified in the reaggregates by recording resting potentials of −40 to −60 mV, and by action potential generation. The action potentials were preceded by pacemaker potentials, had slow rates of rise (<20 V/sec), and were insensitive to tetrodotoxin (TTX). Although the action potentials depend on an inward slow current, D-600 did not block the action potentials of the VSM cells. Reaggregates of atrial cells, produced at the same time for comparison, had larger resting potentials (up to −80 mV), less automaticity, fast rates of rise (mean of about 85 V/sec), and complete TTX sensitivity, thus indicating dependence on fast Na⁺ channels. These findings indicate that identifiable VSM cells can be successfully maintained in primary culture for several weeks, and these cells retain electrical and contractile properties similar to those of smooth muscle cells in intact adult blood vessels. This preparation provides a convenient system for electrophysiological and pharmacological studies of VSM cells.     

Effect of muscle length on electromyogram in a canine diaphragm strip preparation

The relationship between diaphragm electromyogram (EMG), isometric force, and length was studied in the canine diaphragm strip with intact blood supply and innervation under three conditions: supramaximal tetanic (100 Hz) phrenic nerve stimulation (STPS; n = 12), supramaximal phrenic stimulation at 25 Hz (n = 15), and submaximal phrenic stimulation at 25 Hz (n = 5). In the same preparation, the EMG-length relationship was also examined with direct muscle stimulation when the neuromuscular junction was blocked. EMG from three different sites and via two types of electrodes (direct or sewn-in and surface) were recorded during isometric contraction at different lengths. Direct EMGs were recorded from two bipolar electrodes sutured into the strip, one near its central end and the other near its costal end. A third EMG electrode configuration summed potentials from the whole strip by recording potentials between central and costal sites. Surface EMGs were recorded by a bipolar spring clip electrode that made contact with upper and lower surfaces of the muscle strip with light pressure. In all conditions of stimulation with different types of electrodes, all EMGs decreased significantly (P less than 0.05) when muscle length was changed from 50 to 120% of resting length (L0). Minimal and maximal force outputs were observed at 50 and 120% of L0, respectively, in all experiments. The results of this study indicated that the muscle length is a significant variable that affects the EMG recording and that the diaphragmatic EMG may not be an accurate reflection of phrenic nerve activity.(ABSTRACT TRUNCATED AT 250 WORDS)     

The ionic regulation of action potentials in the axon of a stretch receptor neuron of the stick insect (Carausius morosus)

Summary The ionic requirements for the action potentials recorded from the axon of the dorsal longitudinal stretch receptor inCarausius morosus have been studied using extracellular electrodes.In the intact preparation prolonged exposure to sodium-free, calcium-free, or magnesium-free salines produces no observable change in the amplitude of action potentials. Similarly, tetrodotoxin (1×10^–6 M) and cobaltous chloride (1×10^–2 M) are both ineffective in blocking the action potentials.In preparations in which the ionic barrier has been disrupted by removal of the nerve sheath the action potentials show sodium dependence. They are sustained in high sodium salines (150 mM) but are reversibly abolished in sodium-free salines. They are also reversibly abolished in 1×10^–6 M TTX, but unaffected by calcium-free or magnesium-free salines, or by cobaltous chloride (1×10^–2 M).It is concluded that the action currents in the axon of the stretch receptor are carried by sodium ions.     

The relations between prepotential,resting potential,and latent period in frog muscle fibers

1. Prepotentials and action potentials were recorded from amphibian striated muscle fibers. Intracellular electrodes were used for stimulating and recording. The resting potential was varied from 55 to 120 mv. by alterations of the KCl concentration of the Ringer's fluid. The magnitude of the prepotential at the initiation of the spike potential was measured and compared to the resting potential and the latent period (time between stimulus "make" and excitation). The magnitude of this prepotential varied with the resting potential. 2. A large prepotential or cathodal depolarization was required to excite a fiber with a high resting potential. If a fiber with a high resting potential fired late (long latency), the adequate prepotential was larger than if the fiber fired early. Fibers with low resting potentials had smaller adequate prepotentials. Also, the adequate prepotential was independent of the latent period, in these depolarized fibers. 3. If the concentration of Ca⁺⁺ was increased tenfold, the adequate prepotential of depolarized fibers became strongly dependent upon the latency. 4. Fibers with large or normal resting potentials were prone to respond repetitively during the passage of long duration shock, whereas depolarized and Ca⁺⁺-treated fibers were not. 5. The so-called critical membrane potential (which is defined as the transmembrane potential at the point of excitation) was not independent of the resting potential.     

Synaptic transmission in the sixth ganglion of the cockroach: action of 4-aminopyridine.

1. Study was made of the action of 4-aminopyridine (5 X 10(-5) M) on synaptic transmission in the last abdominal ganglion of Periplaneta americana. The 'oil-gap' technique was used to record postsynaptic events in a single giant axon. 2. 4-AP quickly increased the 'background' of postsynaptic activity, which consisted of 'spontaneous' unitary EPSPs and IPSPs. Postsynaptic spikes were also propagated. 3. Both evoked EPSPs (stimulation of cercal nerve XI) and evoked IPSPs (stimulation of cercal nerve X) were greatly increased in amplitude although their duration (half-time) was unaltered. 4. 4-AP triggered presynaptic action potentials in the cercal nerves (recorded with external electrodes). These 'antidromic' potentials appeared singly or sometimes repetitively, especially after electrical stimulation of the cercal nerves. They were often in monosynaptic correlation with unitary EPSPs. 5. Neither the resting potential nor the postsynaptic membrane resistance was modified. 6. There were no changes in the equilibrium potentials of the ions involved in postsynaptic events. 7. The results may be essentially explained by an increase in transmitter release after 4-AP treatment, which may be partly the result of a rise in presynaptic terminal excitability, and partly the result of a lengthening of the presynaptic action potentials.     

Electrophysiological recordings from spontaneously contracting reaggregates of cultured smooth muscle cells from guinea pig vas deferens

Smooth muscle cells were enzymatically dispersed from vasa deferentia of adult male guinea pigs (250-400 g). These cells reassociated in vitro to form monolayers and small spherical reaggregates (0.05-0.3 mm in Diam). Within 48 h of being placed in culture, cells in both types of preparation began to contract spontaneously. The contractions were rhythmic and slow. Cells in the monolayers stopped contracting after approximately 1 wk in vitro, but the reaggregates continued to contract spontaneously for at least 3 wk. Electron microscopy of the reaggregates revealed the presence of thick and thin myofilaments. Overshooting action potentials were recorded in many of the cells penetrated (primarily in reaggregates), and were accompanied by visible contractions of the aggregate or monolayer. Quiescent cells could often be excited by intracellularly applied depolarizing and hyperpolarizing (anodal-break) current pulses. The resting potentials had a mean value of -58 +/- 2 mV. The action potentials were usually preceded by a spontaneous depolarization. The action potentials had slow rates of rise (1--4 V/s) which were unaffected by tetrodotoxin (TTX, 1 microgram/ml), a known blocker of fast Na+ -channels. Verapamil (1 microgram/ml) blocked the action potentials. The mean value of input resistance was 6.9 +/- 0.5 M omega (n = 12). These electrophysiological properties are similar to those of intact adult vas deferens smooth muscle cells. Thus, the cultured adult vas deferens smooth muscle cells retain their functional properties in vitro even after long periods.     

Electrophysiologic study of cultured neurons dissociated from spinal cords and dorsal root ganglia of fetal mice

Spontaneously occurring action potentials and postsynaptic potentials were recorded intracellularly from mouse spinal cord (SC) neurons and dorsal root ganglion (DRG) neurons in mixed SC and DRG cell cultures. In some SC cells, excitatory postsynaptic potentials were evoked by electrical stimulation of a nearby SC or DRG cell. SC and DRG neurons had distinguishing morphologic and electrophysiologic properties. SC neurons usually were elliptical or stellate and had several branched processes whereas DRG cells were most commonly round and had on the average only one process, but occasionally 3 or 4. Calculations from cell measurements revealed that SC neurons had less soma surface area and more process surface area than DRG cells, with a similar total surface area for each class. Lower resting membrane potentials were recorded from SC neurons, but when the capability for action potential generation was tested at comparable steady membrane potentials, most SC and less than half of DRG neurons fired repetitively to electrical stimulation. During the depolarizing and repolarizing phases of SC cell action potentials the rates of change of membrane potential were lower than for DRG cells, which had rapidly rising action potentials and a markedly negative afterpotential. An initially delayed repolarization phase was characteristic of the DRG cell action potential. Cell cultures were prepared by trypsin dissociation of spinal cords with attached spinal ganglia from fetuses of 10, 11, 12, 13, 14, and 17 days gestational age. Cell cultures grown on plastic or collagen were studied electrophysiologically at times from 16 to 94 days.     

Membrane potentials and resistances of giant mitochondria. Metabolic dependence and the effects of valinomycin

The membrane potentials and resistances of giant mitochondria from mice fed cuprizone have been studied. They were found to correspond approx. 10-20 mV, positive inside, and 2 M omega, respectively. These properties were found to be independent of the metabolic state. The microelectrodes were in the inner mitochondrial space since (a) the potentials in the presence of valinomycin depended on the K+ concentration of the medium and magnitude of the K+ diffusion potentials was consistent with the presence of a high internal concentration of K+, (b) almost identical results were obtained with mitochondria from which the external membrane had been removed and the cristae were evaginated, and (c) punch-through experiments, in which the microelectrodes were advanced until they emerged through the other side of the mitochondria, showed an identical membrane potential both in the presence and in the absence of valinomycin. The potentials were stable under a variety of conditions and showed no sign of decay of membrane leakiness. Detailed evidence that the impaled mitochondria are metabolically viable will be presented in a separate publication.     

Electrophysiological control of ciliary motor responses in the ctenophorePleurobrachia

Prey capture by a tentacle of the ctenophore Pleurobrachia elicits a reversal of beat direction and increase in beat frequency of comb plates in rows adjacent to the catching tentacle (Tamm and Moss 1985). These ciliary motor responses were elicited in intact animals by repetitive electrical stimulation of a tentacle or the midsubtentacular body surface with a suction electrode. An isolated split-comb row preparation allowed stable intracellular recording from comb plate cells during electrically stimulated motor responses of the comb plates, which were imaged by high-speed video microscopy. During normal beating in the absence of electrical stimulation, comb plate cells showed no changes in the resting membrane potential, which was typically about -60 mV. Trains of electrical impulses (5/s, 5 ms duration, at 5-15 V) delivered by an extracellular suction electrode elicited summing facilitating synaptic potentials which gave rise to graded regenerative responses. High K+ artificial seawater caused progressive depolarization of the polster cells which led to volleys of action potentials. Current injection (depolarizing or release from hyperpolarizing current) also elicited regenerative responses; the rate of rise and the peak amplitude were graded with intensity of stimulus current beyond a threshold value of about -40 mV. Increasing levels of subthreshold depolarization were correlated with increasing rates of beating in the normal direction. Action potentials were accompanied by laydown (upward curvature of nonbeating plates), reversed beating at high frequency, and intermediate beat patterns. TEA increased the summed depolarization elicited by pulse train stimulation, as well as the size and duration of the action potentials. TEA-enhanced single action potentials evoked a sudden arrest, laydown and brief bout of reversed beating. Dual electrode impalements showed that cells in the same comb plate ridge experienced similar but not identical electrical activity, even though all of their cilia beat synchronously. The large number of cells making up a comb plate, their highly asymmetric shape, and their complex innervation and electrical characteristics present interesting features of bioelectric control not found in other cilia.