Ionic mechanisms of depolarization responses in Helix pomatia neurons to glutamate application

Reversal potentials of transmembrane ionic currents induced by glutamate were determined in various D neurons ofHelix pomatia. Two types of neurons were found with mean reversal potentials of –10.6±1.2 and –40.0±0.6 mV. Neurons of the first group responded under ordinary conditions to glutamate application by a volley of action potentials. Neurons of the second group did not generate action potentials under the same conditions during glutamate application. With an increase in the dose of mediator the amplitude of D responses in these neurons increased only up to a certain limit, without reaching the critical depolarization level of the cell; a fall in the external chloride ion concentration led to a decrease in their reversal potential. The possible ionic mechanisms of glutamate-dependent depolarization responses of these groups of neurons are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 14, No. 6, pp. 572–577, November–December, 1982.     

Modulatory Inputs on Sympathetic Neurons in the Rostral Ventrolateral Medulla in the Rat

1. The first part of this study looks at spontaneously active neurons located in the rostral ventrolateral medulla (RVLM) with projections to the thoracic spinal cord. Sixteen neurons were intracellularly recorded in vivo. Four out of 16 neurons were antidromically activated from the thoracic spinal cord (axonal conduction velocities varied from 1.8 m/s to 9.5 m/s).2. The simultaneous averages of the neuronal membrane potential and arterial blood pressure triggered by the pulsatile arterial wave or the EKG-R wave demonstrated changes in membrane potential (hyperpolarization or depolarization) locked to the cardiac cycle in four neurons in this group. These neurons (three of them bulbospinal) were further tested for barosensitivity by characterizing the responses to electrical stimulation of the aortic depressor nerve. Four neurons responded with inhibitory hyperpolarizing responses characterized as inhibitory postsynaptic potentials (IPSP) to aortic nerve stimulation (onset latency: 32.3 ± 5.0 ms; mean ± SEM).3. In two neurons in the RVLM, one of them characterized as barosensitive, electrical stimulation of the opposite RVLM (0.5 Hz, 1.0 ms pulse duration, 25–100 A) elicited excitatory postsynaptic potentials (EPSPs) with latencies of 9.07 and 10.5 ms. At resting membrane potential, the onset latency of the evoked EPSPs did not change with increasing stimulus intensities. Some of the recorded neurons were intracellularly labelled with biocytin for visualization. They were found in the RVLM.4. These experiments in vivo would support the idea of a functional commissural pathway between the RVLM of both sides.5. Anatomical data have shown that some of those commissural bundle fibers originate in the C1 adrenergic neuronal group in the RVLM. In the second part of this study, we used an intracellular recording technique in vitro to investigate the effects of the indirect adrenergic agonist tyramine on neurons in the RVLM with electrophysiological properties similar to premotor sympathetic neurons in vivo.6. Tyramine (0.5–1 mM) produced a pronounced inhibitory effect with hyperpolarization and increase in membrane input resistance on two neurons characterized as regularly firing (R), and on one neuron characterized as irregularly firing (I). This effect was preceded by a transient depolarization with increases in firing rate.7. These results would indicate that neurons in the RVLM recorded in vitro and with properties similar to premotor sympathetic neurons can be modulated by catecholamines released from terminals probably making synaptic contacts.     

Biphasic increase of apical Cl− conductance by muscarinic stimulation of ht-29cl.19a human colon carcinoma cell line: Evidence for activation of different cl− conductances by carbachol and forskolin

Summary The modulation of ion transport pathways in filtergrown monolayers of the Cl^–-secreting subclone (19A) of the human colon carcinoma cell line HT-29 by muscarinic stimulation was studied by combined Ussing chamber and microimpalement experiments.Basolateral addition of 10^–4 m carbachol induced a complex poly-phasic change of the cell potential consisting of (i) a fast and short (30-sec) depolarization of 15±1 mV from a resting value of –52±1 mV and an increase of the fractional resistance of the apical membrane (first phase), (ii) a repolarization of 22±1 mV leading to a hyperpolarization of the cell (second phase), (iii) a depolarization of 11±1 mV and a decrease of the fractional resistance of the apical membrane (the third phase), (iv) and sometimes, a hyperpolarization of 6±1 mV and an increase of the fractional resistance of the apical membrane (fourth phase). The transepithelial potential increased with a peak value of 2.4±0.3 mV (basolateral side positive). The transepithelial PD started to increase (serosa positive), coinciding with the start of the second phase of the intracellular potential change, and continued to increase during the third phase. Ion replacements and electrical circuit analyses indicate that the first phase is caused by increase of the Cl^– conductance in the apical and basolateral membrane, the second phase by increased K⁺ conductance of the basolateral membrane, and the third phase and the fourth phase by increase and decrease, respectively, of an apical Cl^– conductance. The first and second phase of the carbachol effect could be elicited also by ionomycin. They were strongly reduced by EGTA. Phorbol dibutyrate (PDB) induced a sustained depolarization of the cell and a decrease of the apical fractional resistance. The results suggest that two different types of Cl^– channels are involved in the carbachol response: one Ca²⁺ dependent and a second which may be PKC sensitive.In the presence of a supramaximal concentration of forskolin, carbachol evoked a further increase of the apical Cl^– conductance.It is concluded that the short-lasting carbachol/Ca²⁺-dependent Cl^– conductance is different from the forskolin-activated conductance. The increase of the Cl^– conductance in the presence of forskolin by carbachol may be due to activation of different Cl^– channels or to modulation of the PKA-activated Cl^– channels by activated PKC.The authors are grateful to Drs. Laboisse and Augeron for providing the cell clone, and we thank Prof. Dr. F.H. Lopes da Silva for his comments. This work was supported by a grant from the Dutch Organization for Scientific Research, NWO.     

Effects of applying oxytocin to Helix pomatia neurons. II. Hyperpolarization

The ionic mechanisms of hyperpolarization produced by applying oxytocin (OT) were investigated at the membrane of identifiedHelix pomatia neurons. Two types of neuron were known to exist, in one of which hyperpolarization is produced by a reduction in chloride ions at the membrane and a rise in membrane permeability to potassium ions in the other. In the first of these, response to OT had a reversal potential of –40 mV and decreased when furosemide and tolbutamide were added to the external medium. In the second case, the potential of the reversal of the response to OT was –70 mV. Upon doubling of potassium ion concentration in the external solution it was shifted towards depolarization by 15 mV. It is sugested thatHelix pomatia neurons have different types of OT receptors, some of which, when activated, manifest reduced chloride permeability at the membrane (probably through the cell cyclase system) with a rise in potassium permeability at the membrane in others.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 20, No. 5, pp. 659–666, September–October, 1988.     

Ionic mechanisms of excitatory action of transmitter,exogenous acetylcholine,and serotonin on superior cervical ganglion neurons in rabbits

Ionic mechanisms of EPSP generation and depolarization induced by iontophoretic application of acetylcholine (ACh) and serotonin (5-hydroxytryptamine, 5-HT) — acetylcholine and serotonin potentials — were investigated in neurons of the isolated rabbit superior cervical ganglion by means of intracellular microelectrodes. The reversal potentials (E_r) for EPSP and the ACh-potential were –14.4±1.6 and –16.5±1.2 mV respectively, and they were about the same for the 5-HT potential. In some neurons (about one-third) much more negative values for E_r were obtained for EPSP and the ACh-potential by extrapolation, probably due to an increase in the resistance of their membrane during hyperpolarization. A decrease in the external sodium and potassium concentrations was shown to make E_r for EPSP and the ACh-potential more negative, whereas an increase in the external potassium concentration made it more positive than in normal solution; a change in the external chloride concentration did not alter E_r. It is suggested that the excitatory transmitter and exogenous ACh (and also, probably, 5-HT) share the same ionic mechanism of action of the membrane, which includes an increase in the permeability of the membrane to two ions — sodium and potassium — simultaneously.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 10, No. 6, pp. 637–644, November–December, 1978.     

Effect of penicillin on synaptic activity of motoneurons in the lamprey isolated spinal cord

The effect of penicillin on the membrane potential (MP) and synaptic activity of motoneurons in the isolated spinal cord of the river lamprey was investigated. In cells with a low initial MP (58.7±5.2 mV, n=28), penicillin (2.5 mmole·liter^–1) caused a depolarization, and potentiated excitatory postsynaptic potentials (EPSPs) that were evoked by stimulating spinal tracts and dorsal roots. The EPSPs were potentiated by 80–220% relative to their initial amplitude. In motoneurons with a higher MP (72.0±5.7 mV, n=20), a depolarization did not develop, and the potentiation of EPSPs did not exceed 25–70%. The effects of penicillin were inhibited when antagonists of excitatory and inhibitory amino acids were added to the superfusate. The results obtained imply that the motoneuron membranes have two acceptor sites for penicillin.Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, Saint Petersburg Institute of Biological Research, Belgrade, Yugoslavia. Translated from Neirofiziologiya, Vol. 24, No. 2, pp. 151–160, March–April, 1992.     

Synaptic responses of medullary neurons of turtles to stimulation of the locomotor region

Responses of medullary neurons to microstimulation of the locomotor region by a current of up to 30 µA were studied by intracellular recording in turtles. The resting potential recorded in these neurons was from 22 to 42 mV. Depolarization PSPs (EPSPs) were recorded in 43 neurons, hyperpolarization PSPs (IPSPs) in 12, and mixed in 36. Synaptic discharges were observed in 29 neurons. Of these cells 11 generated action potentials without visible PSPs. The latent period of the PSPs was most frequently between 2 and 8 msec. The time from the beginning of the EPSP to the beginning of the action potential was 1–3 msec if the response index was high, but in the case of weaker stimulation, it began to fluctuate strongly and lengthened. Unitary EPSPs were recorded in 15 neurons and IPSPs in three. Their amplitude was 0.6–0.8 mV, from 2 to 12 times less than the depolarization threshold (1–7 mV). These results, together with those obtained previously by extracellular recording of medullary unit activity in turtles and cats, are used to discuss the possible mechanism of spread of locomotor activity.Institute for Problems in Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 14, No. 2, pp. 122–129, March–April, 1982.     

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.     

Effects of the anion transport inhibitor,SITS, on the proximal straight tubule of the rabbit perfusedin vitro

Summary Conventional microelectrodes were used to study the effects of SITS (4-acetamido-4-isothiocyanostilbene-2,2-disulfonate) on the basolateral membrane potentialVbl of the superficial proximal straight tubule (PST) of the rabbit kidney perfusedin vitro. Addition of 0.1mm SITS to the bathing solution resulted in a slow and irreversible hyperpolarization ofVbl from –42.5±1.17 (37) mV to –77.3±0.83 (52) mV. The new steady-state potential was reached in 10 to 15 min and was accompanied by visible cell swelling. Associated with thisVbl hyperpolarization was: 1) an increased steady-state depolarization (from 6.2±0.77 (17) mV to 25.7±0.83 (29) mV) in response to increasing bath potassium concentration from 5 to 16.7mm (HK); 2) a decreased transient depolarization (from 19.8±1.88 (8) mV to 0.43±0.37 (8) mV) in response to decreasing bath bicarbonate concentration from 22 to 6.6mm at constant bath pH (L-HCO₃); and 3) inhibition of a depolarizing overshoot and a decreased steady-state depolarization (from 35.9±1.84 (12) mV to 4.7±1.37 (13) mV) in response to reducing bath sodium concentration from 144 to zero (0-Na). Sodium, chloride and NMDG (N-methyl-d-glucamine) were used as the substituting ions, respectively. These results are consistent with the presence of a coupled sodium-bicarbonate carrier in the basolateral membrane which is electrogenic and SITS inhibitable. Comparison of the time course of SITS effects on these ion-substitution responses suggests that the inhibition of the bicarbonate exit pathway(s) is the primary event and that the changes inVbl and in the steady-stateVbl responses to HK and 0-Na are secondary events which may be related to changes in intracellular composition and/or basolateral membrane properties.     

Ionic mechanisms of the fast (nicotinic) phase of the acetylcholine response of identified Planorbarius corneus neurons

Responses to electrophoretic application of acetylcholine and suberyldicholine were investigated in identified neurons (LPed-2 and LPed-3) isolated from the left pedal ganglion ofPlanorbarius corneus. When microelectrodes filled with potassium chloride were used the reversal potentials of responses to acetylcholine and suberyldicholine were less negative than when microelectrodes filled with potassium sulfate were used; these reversal potentials were shifted toward depolarization if chloride ions in the medium were replaced by sulfate. These facts indicate that the responses in both LPed-2 and LPed-3 depend on chloride ions. Reversal potentials for acetylcholine and suberyldicholine in LPed-3 were virtually identical (–51 and –50 mV respectively), but in LPed-2 they differed significantly (–46 and –62 mV respectively). Replacement of sodium ions by Tris ions shifted the reversal potential for acetylcholine in LPed-2 toward hyperpolarization but did not change the reversal potential for suberyldicholine. Benzohexonium had the same action. The reversal potential for acetylcholine in medium with a reduced sodium concentration or in the presence of benzohexonium was the same as for suberyldicholine. It is concluded that on neuron LPed-2 acetylcholine activates both acetylcholine receptors which control conductance for chloride ions and acetylcholine receptors which change conductance for sodium ions, whereas suberyldicholine acts only on acetylcholine receptors responsible for the chloride conductance of the membrane.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 12, No. 5, pp. 533–540, September–October, 1980.     

Studies on synaptic transmission in spinal cord cultures: a comparison of postsynaptic actions of classical neurotransmitters with the peptides

The postsynaptic action of the classical neurotransmitter noradrenaline (NA), the reversal potential of the excitatory postsynaptic potential (EPSP) and the effects of divalent cations on EPSPs in dissociated spinal cord cultures are described. In co-cultures of locus coeruleus explant and spinal cord cells, it was found that NA could mimic the response evoked by stimulation of the explant on the spinal cord cells surrounding the explants. Both depolarization and hyperpolarization responses were observed. On a few occasions, a biphasic response consisting of a hyperpolarization followed by a depolarization was observed. The depolarizing response was associated with an increase in input resistance of the membrane. This would suggest that NA may have a facilitatory effect on synaptic transmission. The depolarizations were antagonized by the α-antagonist piperoxane, and were not affected by the β-antagonist propranolol at the concentrations tested, indicating that the receptor mediating these responses is of the α-type. The reversal potential for dorsal root ganglion and spinal cord cells was +8±3.2 mV (mean±s.e.m.), and that for spinal cord and spinal cord cells was ?4±4.3 mV (mean±s.e.m.). These values are different from those previously reported for glutamate in spinal cord cultures. The effects of high and low concentrations of calcium ions on quantal output and mean quantal amplitude or quantal size of the EPSP were further examined. As expected, the cation had an effect mainly on the release process: increasing the concentration of calcium increased the amount of neurotransmitter released, while reducing the concentration of calcium reduced release. Quantal size was slightly or not affected by alteration of external calcium. In comparing the postsynaptic actions of classical neurotransmitters to those of peptides, there is apparently no evidence that the actions of the two groups of agents on central neurons are different. It appears, however, that the peptides generally elicit responses at lower concentrations than the classical neurotransmitters. Further experimentation is required to fully elucidate the actions of peptides on mammalian central neurons.     

EPSPs of masseter motoneurons evoked by stimulation of low-threshold infraorbital nerve afferents in cat

Stimulation of the infraorbital nerve at strengths 1.4–2.5 times higer than the threshold of excitation of A fibers in cats anesthetized with chloralose and pentobarbital evoked EPSPs with an amplitude up to 3.0 mV and a duration of 9–15 msec in 69% of masseter motoneurons after 1.5–3.0 msec. These EPSPs were complex and formed by summation of simpler short-latency and long-latency EPSPs. The short-latency EPSPs appeared in response to infraorbital nerve stimulation at 1.1–1.5 thresholds and had a slow rate of rise (2.5–4.5 msec, mean 3.7±0.4 msec), low amplitude (under 2.0 mV), and short duration (5–6 msec). Their latent period varied from 1.5 to 3.0 msec (mean 2.1±0.2 msec). The shortness of the latent period and its constancy during stimulation of the nerve at increasing strength, and also the character of development of facilitation and inhibition of the EPSP during high-frequency stimulation suggests that these EPSPs are monosynaptic. The slow rate of rise suggested that these EPSPs arise on distal dendrites of the motoneurons. Long-latency EPSPs appeared 7–9 msec after stimulation of the infraorbital nerve at 1.1–1.5 thresholds. Their amplitude reached 1.5–2.0 mV and their duration 7–9 msec. The long duration of the latent period combined with low ability to reproduce high-frequency stimulation (up to 30/sec) points to the polysynaptic origin of these EPSPs.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 9, No. 6, pp. 583–591, November–December, 1977.     

Modulation of the membrane potential of intact guinea pig aortic endothelium

The role of different ion conductances in regulation of the membrane potential (MP) of resting and agonist-stimulated intact endothelium from the guinea pig aorta was investigated. Under resting conditions, the MP measured by the patch-clamp technique varied within the range from –29 to –56 mV (the mean value of –40.8 ± 8.1 mV). Blockers of anomalous (inward) rectifier potassium channels cesium (100 µM) and barium (100 µM) exerted no effect on the MP of endothelium. Superfusion of preparations with calcium-free solution and application of 2 mM nickel depolarized the endothelium. ATP (10 µM) induced hyperpolarization of endothelium with the mean amplitude of 11.4 ± 0.6 mV. The initial phase of this hyperpolarization depended on the external potassium concentration and on the state of intracellular calcium stores, whereas the prolonged phase required the presence of external calcium. In the absence of external calcium, in 25% of recordings transient hyperpolarization was followed by depolarization, which was not observed after substitution of external NaCl for choline. It was concluded that basal activity of calcium-dependent potassium channels contributes to the regulation of the MP of resting endothelium. Stimulation with ATP led to activation of calcium-dependent potassium and nonselective cationic channels. Activation of the former channels produced the initial phase of hyperpolarization, whereas activation of the second channel type evoked the prolonged phase of hyperpolarization.Neirofiziologiya/Neurophysiology, Vol. 28, No. 6, pp. 260–266, November–December, 1996.     

Secondary hair cells and afferent neurones of the squid statocyst receive both inhibitory and excitatory efferent inputs

Summary Intracellular recordings were obtained from the hair cells and afferent neurones of the angular acceleration receptor system of the statocyst of the squid,Alloteuthis subulata. Electrical stimulation of the efferent fibres in the crista nerve (minor) evoked responses in all of the secondary hair cells recorded from (n=211). 48% of the secondary air cells responded with a small depolarization, 15% with a hyperpolarization, and 37% with a depolarization followed by a hyperpolarization. The depolarizations and hyperpolarizations had mean stimulus to response delays of 6.7 ms and 24 ms, and reversal potentials of about –1 mV and –64 mV, respectively. Both types of potential increased in amplitude, up to a point, when the stimulus shock was increased and facilitation and/or summation effects could be obtained by applying multiple shocks. These data, together with the fact that both responses could be blocked by bath application of cobalt or cadmium, indicate that the secondary hair cells receive both inhibitory and excitatory efferent inputs and that these are probably mediated via chemical synapses. No efferent responses were seen in the primary hair cells but both depolarizing and hyperpolarizing efferent responses were obtained from the afferent neurones.     

Chemosensitivity of single smooth muscle cells to acetylcholine, noradrenaline, and histamine in vitro

Electrical responses to acetylcholine, noradrenaline, and histamine were recorded from solitary smooth muscle cells. Iontophoresis of each transmitter elicited three fast responses: a hyperpolarization, a depolarization, or a biphasic hyperpolarization-depolarization. Each transmitter activated a specific receptor since responses were specifically blocked by antagonists, two transmitters elicited different responses in solitary cells, and desensitization of response to one transmitter did not cause desensitization of responses to other transmitters. Responses were due to increased ion conductances since input resistance decreased during responses and reversal potentials were measured for depolarizing responses (-5 mV) and hyperpolarizing responses (-60 mV). Regional differences in transmitter sensitivity were mapped on solitary cells. Biphasic responses were due to simultaneous activation of receptors mediating hyperpolarizing responses and receptors mediating depolarizing responses which were segregated in the cell membrane. Noradrenaline enhanced action potential amplitude by regulation of voltage-dependent ion conductances. Finally, noradrenaline and histamine elicited periodic hyperpolarizing potentials, which may be due to increased intracellular Ca++.     

Fused cells of frog proximal tubule: II. Voltage-dependent intracellular pH

Summary Experiments were performed in intact proximal tubules of the doubly perfused kidney and in fused proximal tubule cells ofRaha esculenta to evaluate the dependence of intracellular pH (pH_i) on cell membrane potential applying pH-sensitive and conventional microelectrodes. In proximal tubules an increase of the K^– concentration in the peritubular perfusate from 3 to 15 mmol/liter decreased the peritubular cell membrane potential from –55±2 to –38±1 mV paralleled by an increase of pH _i , from 7.54±0.02 to 7.66±0.02. The stilbene derivative DIDS hyperpolarized the cell membrane potential from –57 ± 2 to –71 ±4 mV and led to a significant increase of the K^–-induced cell membrane depolarization, but prevented the K^–-induced intracellular alkalinization. Fused proximal tubule cells were impaled by three microelectrodes simultaneously and cell voltage was clamped stepwise while pH _i changes were monitored. Cell membrane hyperpolarization acidified the cell cytoplasm in a linear relationship. This voltage-induced intracellular acidification was reduced to about one-third when HCO₃ ions were omitted from the extracellular medium. We conclude that in proximal tubule cells pH _i depends on cell voltage due to the rheogenicity of the HCO ₃ ^– transport system.     

Investigation of electrophysiological responses of Neurospora crassa to blue light

The influence of light in a spectrum range of 350–500 nm 20 W m^-2 (20,000 erg · cm^-2 · s^-1) has been studied in the mycelial cells of Neurospora crassa. Light-induced input resistance and membrane potential changes can be measured by means of intracellular microelectrodes. The value of the input resistance reached maximum after a 2–5 min illumination. The maximum hyperpolarization of the cell membrane reaching 30–40 mV was observed after 20–25 min illumination, when the input resistance values did not differ significantly in the illuminated and non-illuminated cells.     

Voltage-gated ion conductances corresponding to regenerative positive and negative spikes in the dinoflagellateNoctiluca miliaris

Depolarization-activated and hyperpolarization-activated ion conductances in the membrane of a marine dinoflagellateNoctiluca miliaris were examined under voltage-clamp conditions.Noctiluca exhibited a transient inward current in response to a step depolarization from a holding potential level of –80 mV to a potential level more positive than –50 mV. The I–V relationship for the current exhibited typical N-shaped characteristics similar to those of most excitable membranes. The current was inactivated by a membrane depolarization. The reversal potential of the current shifted in hyperpolarizing direction when the external Na⁺ concentration was lowered. The transient inward current is assumed to be responsible for the Na⁺-dependent positive spike in non-clamped specimens ofNoctiluca.Noctiluca exhibited a transient outward current in response to a step hyperpolarization from a holding potential level of –20 mV to a potential level more negative than –30 mV. The I–V relationship for the current was a typical N-shape as if it was turned 180° around its origin. The outward current showed a two-step exponential time-decay. The outward current was inactivated by a membrane hyperpolarization. The reversal potential shifted in the depolarizing direction when the external Cl^– concentration was lowered. The transient outward current is responsible for the Cl^–-dependent negative spike in non-clamped specimens ofNoctiluca.Abbreviations ASW artificial seawater - TRP tentacle regulating potentials - TTX tetrodotoxin     

Effect of bicarbonate,pH, methazolamide and stibenes on the intracellular potentials of cultured bovine corneal endothelial cells

Summary Micropuncture of cultured bovine corneal endothelial cells led to registrations stable for hours. Intracellular potentials were mainly in the range of –40 to –55 mV, average 46.3±0.6 mV (sem). Changes of extracellular [HCO ₃ ^– ] led to voltage transients, their amplitude depending logarithmically on [HCO ₃ ^– ] with a mean slope of 37.3±8.8 (sd) mV. After removal of bicarbonate/CO₂, a steady-state depolarization was seen. This steady-state depolarization, but not the voltage transients, could be reduced by 1mm Ba⁺⁺. After removal of bicarbonate, the voltage response to changes of extracellular potassium was reduced. Alteration of pH _i induced by permeable buffers (butyrate, glycodiazine and ammonium) also resulted in voltage transients, internal acidification being correlated with a hyperpolarization, and internal alkalinization with a depolarization. Also changes of external pH caused voltage responses, alkalinization causing a hyperpolarization, acidification a depolarization. Methazolamide, an inhibitor of carbonic anhydrase, as well as stilbenes (SITS or DIDS) caused a reduction of the voltage response to HCO ₃ ^– and pH. Their effects were additive. It is suggested that corneal endothelial cells possess one or two electrogenic transporters for HCO ₃ ^– or related species, one of which is inhibitable by stilbenes.     

Effects of conditioning polarization on the membrane ionic currents in rat myometrium

Summary Membrane ionic currents were measured in pregnant rat uterine smooth muscle under voltage clamp conditions by utilizing the double sucrose gap method, and the effects of conditioning pre-pulses on these currents were investigated. With depolarizing pulses, the early inward current was followed by a late outward current. Cobalt (1mm) abolished the inward current and did not affect the late outward currentper se, but produced changes in the current pattern, suggesting that the inward current overlaps with the initial part of the late outward current. After correction for this overlap, the inward current reached its maximum at about +10 mV and its reversal potential was estimated to be +62 mV. Tetraethylammonium (TEA) suppressed the outward currents and increased the apparent inward current. The increase in the inward current by TEA thus could be due to a suppression of the outward current. The reversal potential for the outward current was estimated to be –87 mV. Conditioning depolarization and hyperpolarization both produced a decrease in the inward current. Complete depolarization block occurred at a membrane potential of –20 mV. Conditioning hyperpolarization experiments in the presence of cobalt and/or TEA revealed that the decrease in the inward current caused by conditioning hyperpolarization was a result of an increase in the outward current overlapping with the inward current. It appears that a part of the potassium channel population is inactivated at the resting membrane potential and that this inactivation is removed by hyperpolarization.