Separation of sodium and calcium currents in the somatic membrane of mollusc neurones. With an Appendix by Yu A. Shakhovalov

Abstract

SUMMARY1. Characteristics of the transmembrane ionic currents under controlled changes in ionic composition of extra-and intracellular medium were studied in isolated neurones from the ganglia of molluscs, Helix pomatia, Limnea 8taJnali8 and Planorbis corneus. The neurones were investigated by a new technique which allows for dialysis of their interior and for clamping of the potential at the surface membrane without using micro-electrodes.2. Replacement of K ions by Tris inside the neurones eliminated the outward K current so that the actual time course of the inward current could be measured. The latter was separated into two additive components, one of which was carried by Na ions and the other one by Ca ions.3. Both inward currents were unaltered by tetrodotoxin (TTX); however, Ca current could be separately blocked by externally applied Cd ions (Kd = 7*2 x 10-5 M) and by the use of fluoride as an intracellular anion.4. No reversal of Na inward current could be achieved in neurones dialysed with Na-free solution, indicating the absence of outward current carrying ions through the corresponding channels. With 5 mM-Na inside the cell, the equilibrium potential was close to the value predicted by the Nernst equilibrium.5. A non-specific outward current could be detected in K-free cells at membrane potentials exceeding 20-40 mV. Its time course was proportional to 1-exp (-t/Tnr). Cd ions depressed this current. The presence of the non-specific outward current made an exact measurement of the equilibrium potential for the Ca inward current impossible.6. The kinetics of Na inward currents could be described by m3h and those of the Ca current by m2h law. The corresponding values for Vm = 0 are: rm(Na) = 1.1 + 05 msec, rm(Ca) = 2-4 + 1*0 msec, rh(Na) = 7-9 + 2-0 msec. The inactivation of Ca current included two first-order kinetic processes with Th1 = 50 + 10 msec and Th = 320 + 30 msec.21-2 P. G. KOSTYUK AND 0. A. KRISHTAL 7. The data presented are considered to be a proof of the existence of separate systems of Na and Ca ion-conducting channels in the nerve cell membrane.

Kinetics and selectivity of a low‐voltage‐activated calcium current in chick and rat sensory neurones.

“…channels during internal perfusion with high intracellular Ca2+ and F-agrees with previous reports on molluscan (Kostyuk, Krishtal & Shakhovalov, 1977; and different vertebrate sensory neurones (Bossu et al 1985;Carbone & Lux, 1985). Discrepancies exist mainly in the critical concentration of intracellular Ca2+ needed for complete removal of h.v.a.…”

Apamin as a selective blocker of the calcium-dependent potassium channel in neuroblastoma cells: voltage-clamp and biochemical characterization of the toxin receptor.

“…The culture dish was placed on the warm stage of an inverted microscope (Leitz Diavert) and the temperature was maintained at about 30°C. Experiments were performed by using a suction pipette method which combines internal perfusion with voltage clamp ofisolated cells (16)(17)(18)(19). The suction pipette had a tip diameter of about 10 ,um.…”

Accelerating effects of pentobarbitone on the inactivation process of the calcium current in Helix neurones

“…As to calcium current (ICa), the inactivation process (the decay phase of ICa) has been analysed in various tissues, and ICa after reaching its peak, is inactivated in a voltage-and current-dependent manner (Kostyuk, Krishtal & Shakhovalov, 1977;Akaike, Lee & Brown, 1978;Brehm & Eckert, 1978;Tillotson, 1979;Brown, Morimoto, Tsuda & Wilson, 1981;Plant & Standen, 1981). So far as we know, no drug has been found to accelerate the decay of ICa* We show here that pentobarbitone accelerates the decay of ICa in snail neurones.…”