Sodium and calcium fluxes in a clonal nerve cell line.

Abstract

SUMMARY1. 22Na+ and 45Ca2+ fluxes were studied in the clonal nerve cell line PC12. Three distinct types of ion channels were found: (a) voltage-dependent Na+ channels, (b) voltage-dependent Ca2+ channels, and (c) acetylcholine-activated channels permeable to both ions.2. 22Na+ uptake through voltage-dependent Na+ channels is induced by veratridine and scorpion venom, and is inhibited 50 % by 5 x 10-7 M-tetrodotoxin and greater than 98 % by 5 x 106 M-tetrodotoxin.3. o*Ca2+ uptake through voltage-dependent Ca2+ channels is induced by depolarizing the cells in 50 mM-KCl. This flux is not dependent on the presence of Na+ in the medium and is insensitive to 5 x 106 M-tetrodotoxin. However, 1 mM-Mn2+ causes a 95 % inhibition of K+-induced 45Ca2+ uptake.4. Veratridine and scorpion venom also induce voltage-dependent 45Ca2+ uptake which can be blocked by ImM-Mn2+. In contrast to KCl-induced 45Ca2+ uptake, this flux is completely blocked by 5 x 106 M-tetrodotoxin and is abolished by removal of Na+ from the medium. Thus the depolarizing stimulus for Ca2+ uptake in this case is Na+ influx through voltage-dependent Na+ channels.5. Carbamylcholine induces both 22Na+ and 45Ca2+ fluxes which are blocked by nicotinic cholinergic antagonists with the exception of ac-bungarotoxin. The 22Na+ flux occurs exclusively via acetylcholine receptor channels, as evidenced by the lack of effect of 5 x 106 M-tetrodotoxin. In the presence of Na+, almost all of the 45Ca2+ uptake can be blocked by 1mM-Mn2+ and thus occurs via voltage-dependent Ca2+ channels which are activated by the depolarizing Na+ influx. 6-8% of the total 45Ca2+ flux, however, is insenstitive to 1 mM-Mn2+, suggesting that this portion of the uptake occurs via the acetylcholine receptor channels. In Na+-free medium, the Mn2+-resistantf45Ca2+,component increases to 40 % of the total uptake, apparently due to lack of competition from Na+ for the acetylcholine receptor channels. This receptor-linked flux still causes sufficient depolarization to induce the additional 60 % of the Ca2+ flux through voltage-dependent, Mn2+ sensitive Ca2+ channels.6. Mn2+ inhibits Ca2+ flux through voltage-dependent Ca2+ channels by competing for entry through these channels. 50 mM-KCl induces 54Mn2+ fluxes in PC12 cells that are comparable in magnitude to 45Ca2+ fluxes.7. In normal saline 45Ca2+ efflux from PC12 cells is several times more rapid than in Na+-free medium, indicating the presence of a Ca2+-Na+ exchange mechanism.

Chromaffin cell action potentials and their possible role in adrenaline secretion from rat adrenal medulla.

“…Part of this discrepancy between adrenaline output and level of depolarization may be due to the Ca permeability of the ACh receptor channel (Douglas, Kanno & Sampson, 1976b;Douglas & Rubin, 1963). If this is the case then this is in contrast to results obtained from an adrenal chromaffin cell line where stimulation of catecholamine secretion (Ritchie, 1979) by cholinergic agonists is predominantly due to Ca influx through the voltage dependent Ca channel (Stallcup, 1979 (Kidokoro, 1975;Taraskevich & Douglas, 1977;Duffy, Vincent, Fleury, Pasquier, Gourdji & Tixier-Vidal, 1979;Ozawa & Kimura, 1979). Recently it was shown that dopamine has an inhibitory effect on the spontaneous spike frequency of cells in the pars intermedia of the pituitary gland.…”

“…Stimulation by ACh may additionally involve Ca influx through the ACh receptor channel (Douglas & Rubin, 1963). However, in physiological salt concentrations this appears to be a minor pathway (Stallcup, 1979; Ritchie, 1979), at least in the adrenal medullary cell line studied.…”

“…In each instance release requires external Ca ions (Douglas & Rubin, 1961;Ishikawa & Kanno, 1978). During long term depolarization (several minutes) the entry of Ca into the cell Stallcup, 1979) and subsequent secretion Ritchie, 1979) is apparently mediated by influx through slowly inactivating voltage dependent Ca channels. Stimulation by ACh may additionally involve Ca influx through the ACh receptor channel (Douglas & Rubin, 1963).…”

Inhibition of Ion Channels by Hirsutine in Rat Pheochromocytoma Cells.

“…3). A consider able part of nicotine-evoked catecholamine-re lease depends on Ca-influx mediated through Ca channels secondly activated by depolariza tion in PC12 cells (22,23). Thus, the potent inhibition by hirsutine of the dopamine-release may be due to blockade by hirsutine of Ca channels (Fig.…”

Effect of OM-853, a Cerebral Metabolic Ameliorator, on Ambulatory Activity and Passive and Active Avoidance Responses in Mice and Mongolian Gerbils

“…5A) was not largely affected by 10 pM hirsuteine. A con siderable part of the nicotine-evoked catecholamine re lease depends on Ca-influx mediated through Ca channels secondarily activated by depolarization in PC 12 cells (22,23). Although hirsuteine (1-10 pM) inhibited Ba currents (Fig.…”