Action of calcium on the somatic membrane of mollusk giant neurons

Early membrane currents of the isolated neuron soma of the mollusksHelix pomatia,Limnaea stagnalis, andPlanorbis corneus in normal and sodium-free solutions differing in their calcium ion concentration were investigated by the voltage clamp method. The early inward current was shown to continue when the sodium ions in the external solution were replaced by an equivalent number of calcium ions and to be increased with an increase in the concentration of those ions in all neurons of these mollusks investigated. A change in the calcium concentration in the external solution shifted the inactivation curves and also the curves of conductance for the inward current along the potential axis. It is concluded that a system of calcium channels exists in the somatic membrane of neurons in these species of mollusks.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 5, No. 6, pp. 621–627, November–December, 1973.     

Interaction between sea anemone toxin BgTX8 and ionic channels of neurons isolated from mammals

The action of the toxin BgTX₈ separated from the sea actiniaBunodosoma granolifera on transient tetrodotoxin-sensitive sodium and outward potassium currents of units isolated from rat sensory ganglia was investigated using techniques of voltage clamping at the membrane and intracellular perfusion. It was found that BgTX₈ decelerates the inactivation kinetics but has little effect on activation kinetics of sodium current. At the same time, a 5–10% increase in the amplitude of inward current was often observed at holding potentials of about –100 to –120 mV at the membrane. The dissociation constant of the receptor-toxin equals 4×10^–6 M and is adequately described by Langmuir's isotherm. It was also established that intracellular perfusion of neurons with anemone toxin-containing solution leads to a reduction in the amplitude of sodium current and decelerates its inactivation process. Suppression of outward potassium current was also noted.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Institute of Brain Research, Academy of Sciences, Havana, Cuba. Translated from Neirofiziologiya, Vol. 20, No. 1, pp. 32–37, January–February, 1988.     

Effects of extracellular potassium ions on outward potassium current dependent on extracellular calcium ions

Changes in outward potassium current occurring in response to changes in the concentration of potassium ions in the extracellular medium were investigated in unidentified neurons isolated fromHelix pomatia using an intracellular perfusion technique. It was found that introducing potassium ions (5–10 mM) into the extracellular solution produces a reversible increase in the component of outward potassium current which is dependent on extracellular calcium ions. Increased amplitude of this component occurs as a result of attenuated inactivation of the current under the action of extracellular potassium.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 19, No. 3, pp. 351–356, May–June, 1987.     

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.     

Mechanisms of generation of long action potentials in barium solutions

Under voltage clamp conditions ionic currents of neurons of the molluskHelix were studied in solutions containing barium ions. Replacement of the calcium ions in the normal external solution by barium ions led to displacement of the potassium conductivity versus membrane potential curve along the voltage axis toward more positive potentials and also to a decrease in the limiting value of the potassium conductance of the membrane. In sodium- and calcium-free solutions containing barium ions two fractions of the inward current are recorded: quickly (I) and slowly (II) inactivated. The rates of activation of these fractions are comparable. Barium ions are regarded as carriers of both fractions of the inward current. It is postulated that both fractions of the barium current are carried along the calcium channels of the membrane.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 9, No. 4, pp. 408–414, July–August, 1977.     

Effect of the alkaloid lappaconitine on ionic currents through the somatic membrane ofHelix pomatia neurons

The effect of the alkaloid lappaconitine on passive ion transport through the somatic membrane of identified neurons of the snailHelix pomatia was studied under voltage clamp conditions. In a concentration of 4 mM lappaconitine has a reversible blocking action on the calcium channels of the excitable membrane. To study the effect of the alkaloid on inward sodium currents a solution in which calcium ions were replaced by the equivalent number of magnesium ions was used. Lappaconitine has no appreciable effect on the inward sodium current.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Institute of Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Neirofiziologiya, Vol. 11, No. 5, pp. 469–474, September–October, 1979.     

Single potassium channel of anomalous (inward) rectification in mollusk neurons

Currents passing through individual potassium channels with anomalous (inward) rectification were recorded at the neuronal membrane ofPlanorbarius corneus using the patch clamp technique. These currents could be detected, whether in "right side out" or "inside out" configurations in the presence of 50 mM potassium ions or one of the potassium channel blockers: tetraethylammonium (TEA), barium, or cesium (2–20 mM) on the external side of the membrane. Inward currents were observed in individual channels at potentials more negative than level of potassium equilibrium potential (E_k); conductance of these measured 81±12 pS (n=11). At more positive potentials than E_k, conductance fell to zero. Potassium channels with anomalous (inward) rectification inPlanorbarius corneus resemble equivalent channels in other cells in their kinetics: time scale of the open state may be described by a single exponential function. This would imply that the ionic channel has a single open state. Time scale of the closed state was biexponential, thus indicating the possible existence of two kinetically different nonconducting states of the potassium channel with anomalous (inward) rectification at the neuronal membrane ofPlanorbarius corneus.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 21, No. 1, pp. 31–38, January–February, 1989.     

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.     

Blocking action of calmidazolium and chlorpromazine on outward potassium current dependent on extra-cellular calcium ions

The effects of the calmodulin antagonists, calmidazolium (R 24571) and chlorpromazine on delayed outward potassium current at the somatic membrane were investigated in non-identified intracellularly perfused neurons isolated fromHelix pomatia. Voltage was clamped at the membrane. Extracellular application of these substances produced effective depression of the outward current. This effect even occurred at test substance concentrations of 10^–9–10^–8 M. Block-ade of delayed outward current was produced mainly as a result of suppressing the potassium current component dependent on intracellular potassium ions (I_k(Ca/in)). The possibility that the receptor for intracellular calcium responsible for modulating this current may be of a calmodulin-like nature is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 19, No. 3, pp. 356–361, May–June, 1987.     

Effect of theophylline on electrical activity of bursting type in an identified Helix pomatia neuron

The effect of theophylline, an inhibitor of cyclic nucleotide phosphodiesterase, on electrical activity of bursting neuron RPa1 ofHelix pomatia was investigated. In a concentration of 1 mM theophylline, when added to the external solution, increases the frequency and number of action potentials in the burst and also the duration of the inter-burst interval and the amplitude of membrane potential waves. In concentrations of 2.5 and 5.0 mM theophylline leads to reversible inhibition of bursting activity. During rinsing this activity rises to a higher level and then returns to the original value. The action of theophylline develops and disappears (as a result of rinsing) in the course of 1–5 min, depending on concentration of the inhibitor. It is suggested that electrical activity of the molluscan bursting neuron is controlled through the cyclic nucleotide system.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 13, No. 1, pp. 75–79, January–February, 1981.     

Role of calcium ions in response generation by the scallop abdominal sensory organ

The effect of calcium-free solution, cadmium ions, and theophylline on the global spike response in a nerve arising from the abdominal sensory organ of the scallopPatinopecten yessocensis, evoked by mechanical stimulation of that organ, was investigated. Removal of Ca ions from the external medium and addition of 10 mM CdCl₂ to it were shown to reversibly inhibit the combined spike response. Addition of theophylline to the external medium in a concentration of 5 mM caused an increase in amplitude of the spike response. These results indicate that Ca ions play a direct part in transformation of the mechanical stimulus into an electrical signal, and also that this process may be regulated by intracellular cAMP-dependent reactions.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Pacific Oceanologic Institute, Far Eastern Scientific Center, Academy of Sciences of the USSR, Vladivostok. Translated from Neirofiziologiya, Vol. 16, No. 4, pp. 475–480, July–August, 1984.     

Action of calcium ions on channels of inward and outward currents in the molluscan neuron membrane

Changes in the characteristics of activity of sodium, calcium, and potassium channels in the surface membrane during variation of the calcium ion concentration in the extracellular and intracellular medium were investigated by the voltage clamp method during intracellular dialysis of isolated neurons of the mollusksLimnea stagnalis andHelix pomatia. Besides their direct role in passage of the current through the membrane, calcium ions were shown to have two actions, differing in their mechanism, on the functional properties of this membrane. The first was caused by the electrostatic action of calcium ions on the outer surface of the membrane and was manifested as a shift of the potential-dependent characteristics of the ion transport channels along the potential axis; the second is determined by closer interaction of calcium ions with the specific structures of the channels. During the action of calcium-chelating agents EGTA and EDTA on the inner side of the membrane the conductivity of the potassium channels is substantially reduced. With an increase in the intracellular free calcium concentration the conductivity is partially restored. The action of EGTA and EDTA on the outer side of the membrane causes a substantial decrease in the ion selectivity of the calcium channels and changes the kinetics of the portal mechanism. These changes are easily abolished by rinsing off the chelating agents or by returning calcium ions to the external medium. A specific blocking action of an increase in the intracellular free calcium concentration on conductivity of the calcium channels was found.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 9, No. 1, pp. 69–77, January–February, 1977.     

Action potentials of the mollusk giant neuron with changes in extracellular concentrations of sodium and calcium ions

The action potential (AP) of the giant neuron of the molluskPlanorbis corneus exhibits an increased sensitivity of the spike overshoot to external sodium concentration in solutions containing a significantly lowered concentration of calcium. These results suggest that during the AP both sodium and calcium ions may act as carriers of the inward-directed current. During repeated responses the role of calcium ions in AP generation increases while that of sodium decreases. A delay in repolarization can occasionally be observed at the beginning of the falling phase of the AP. This delay is considered to be a result of a decrease in efficiency of the repolarizing action of the outward potassium current due to competition from a current entering the cell at the time of the falling phase. Results suggest that the carrier of this inward current is calcium.A. A. Bogomolets' Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 1, No. 1, pp. 109–117, July–August, 1969.     

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.     

Effects of applying oxytocin to Helix pomatia neurons. I. Depolarization

Inward current produced by applying oxytocin (OT) to the neuronal soma (OT_I) current) under conditions of voltage-clamping at the cell membrane was investigated inHelix pomatia. Replacing sodium with Tris ions in the external medium produced a considerable decline in OT_I current. A reduction in the external concentration of chlorine ions by replacement with HEPES ions induced an increase in OT_I current and a shift in its current-voltage relationship towards depolarization values. The presence of furosemide in the external solution reversibly inhibited OT_I current. This current likewise declined reversibly following external application of imidazole and tolbutamide but was increased by theophylline action. It was inferred that OT receptors are present on the surface membrane of someHelix neurons which, when activated, lead to increased chlorine permeability — a process apparently mediated via the cyclic nucleotide system.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR. Kiev. Translated from Neirofiziologiya, Vol. 20, No. 5, pp. 652–659, September–October, 1988.     

Influence of lithium ions on the electrical activity of nerve cells of the leech

The influence of lithium ions on the electrical activity of the nerve cells of the leech,Hirudo medicinalis, was investigated by the method of microelectrode recording. It was discovered that the electrical activity of the giant nerve cells disappears rapidly in a solution with lithium ions. In such a solution, the membrane of these cells is depolarized by 5–7 mV; however, polarization of the cells with direct current does not lead to a restoration of their activity. Possible mechanisms of the inability of lithium ions to replace sodium ions in the generation of the action potentials of leech nerve cells are discussed.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 2, No. 6, pp. 636–642, November–December, 1970.     

Separation of potassium and calcium channels in the nerve cell soma membranes

Investigation of isolated neurons ofHelix pomatia during intracellular dialysis revealed differences in the sensitivity of the channels for the outward potassium and inward calcium currents to changes in pH of the external medium. As a result of this difference, considerable separation of the regions of activation of the currents was obtained along the potential axis in solutions with low pH and the characteristics of the inward and outward currents could be studied during their minimal application. Channels for the outward current were shown to have some permeability for tris ions (P_Tris:P_K=0.05), which is the reason why it is impossible to block this current completely by replacing the intracellular potassium by Tris. Channels for the inward calcium current are characterized by slow inactivation, with a first-order kinetics; their momentary voltage-current characteristic curve reveals significant Goldman's rectification. The selectivity of the calcium channels for other bivalent cations is: Ba:Sr:Ca:Mg=2.8:2.6:1.0:0.2.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 10, No. 6, pp. 645–653, November–December, 1978.     

Involvement of calcium-binding membrane components in neurophysiological mechanics of habituation in Helix pomatia

Dynamics of binding between calcium and hydrophobic membrane components were investigated in vivo in identified neurons ofHelix pomatia while producing habituation to tactile stimuli using a fluorescent chlortetracycline probe technique. A decline in the concentration of membrane-bound calcium (Ca _b ²⁺ ) and likewise in the intensity of electrophysiological response was found in the "command" neurons of defensive behavior when applying a train of stimuli. An increase in Ca _b ²⁺ was noted in the sensory neuron studied and in the spiracle motoneurons. It proved difficult to produce habituation in these cells fulfilling standard electrophysiological criteria. Hydrophobe-hydrophil transfer of calciumbinding molecules is thought to accompany production of habituation in nerve cells.P. K. Anokhin Institute of Normal Physiology, Academy of Medical Sciences of the USSR, Moscow. I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 21, No. 5, pp. 605–612, September–October, 1989.     

Functional characteristics of potassium channels at the neuronal somatic membrane of Lymnaea stagnalis at different ages

Peak amplitude of transient and delayed outward current declined in identified nerurons of the olderLymnaea stagnalis specimens. This could be due to age-dependent alteration not in the total neuronal surface area but in the phospholipid content of the membrane. Age-dependent dynamics of potassium channel function could underlie the alteration observed in neuronal function during ageing.Institute of Gerontology, Academy of Medical Sciences of the USSR, Kiev. Translated from Neirofiziologiya, Vol. 21, No. 1, pp. 3–7, January–February, 1989.     

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.