[Increase in the after-depolarization of a single node of Ranvier of isolated nerve fibers after application divalent (Ca2+, Ba2+, Mn2+, Zn2+, Ni2+) and trivalent (La2+) ions]

Abstract

It has been shown that a 5.5-fold increase in Ca2+ concentration in the external solution leads to the rise in negative after depolarization (NAD) of a single node of Ranvier of myelinated nerve fibres isolated from Rana ridibunda. The NAD amplitude and duration increase 1.3-fold and 1.6 fold, respectively. Introduction in the external solution of Ba2+ and Mn2+ (up to 10 mM) leads to a negligible increase in NAD. A more pronounced effect on action potential and NAD of the node of Ranvier is exerted by Zn2+ and Ni2+ (1.5 and 10 mM), entailing a 5-fold and 10-fold increase in NAD duration. Combined action of Ni2+ and tetraethylammonium brings about a depolarization plateau lasting 50-150 ms followed by the development of NAD lasting 14-30 ms. Introduction in the external solution of La3+ produces a 3--7-fold increase in NAD. Under all exposures cited the decrease in NAD in exponential in character, as is the case in normal Ringer's solution. The changes in NAD described are likely to be accounted for by the effect of the ions on the time constants of the processes of activation and inactivation.