Effects od divalent cations on neuromuscular transmission in the chick
Journal
European Journal of Pharmacology
Journal Volume
64
Journal Issue
4
Pages
259-269
Date Issued
1980
Author(s)
Lin-Shiau S.-Y.
Abstract
In comparative studies on the effects of nine divalent cations (Mn2+, Co2+, Ni2+, Cd2+, Zn2+, Sr2+, Cu2+, Ba2+ and UO22+ on twitch responses to indirect and direct stimulations, on acetylcholine response and on Ca2+ uptake, it was found that Cd2+ was the most potent in inhibiting transmitter release from the motor nerve terminals but was without appreciable effect on the chick biventer cervicis muscle. Mn2+, Co2+, Ni2+ and Zn2+ were less potent than Cd2+ in producing inhibition at presynaptic sites but were morep potent at postsynaptic sites. By contrast, UO22+ potentiated twitch responses to indirect stimulation and induced a contracture of the muscle in the presence of physostigmine. Cu2+ and Ba2+ were particularly potent in inducing a contracture and at higher concentrations abolished twitch responses to indirect and direct stimulation. Sr2+ at the very high concentration of 22 mM had only a week inhibitory action on twitch responses but was the only cation capable of substituting for Ca2+ in inducing contraction. The studies on the effects of these cations on denervated muscle also led to the conclusion that Cd2+ and UO22+ act mainly on presynaptic nerve terminals and that Mn2+, Co2+, Ni2+ and Zn2+ act on presynaptic sites preferentially to postsynaptic sites while Cu2+ and Ba2+ act mainly on muscle. The effects of these cations can be antagonized by high Ca2+ (10 mM) but those of Cu2+ cannot. Cysteine (2.5p mM) antagonized the effects of all the cations except Mn2+, Ba2+ and UO22+. d-Tubocurarine suppressed the contracture induced by UO22+ but not that induced by Cu2+ and Ba2+. These cations affected 45Ca2+ uptake and ionic contents of the muscle differently. 45Ca2+ uptake of the muscle was decreased by Mn2+, Co2+ and Ni2+, not altered by UO22+ but increased by Cd2+, Zn2+, Sr2+, Cu2+ and Ba2+. In addition to greatly increasing 45Ca2+ uptake, Cu2+ also increased calcium and sodium but decreased the potassium content of muscle. Zn2+ and Sr2+ increasedp the calcium content slightly but the other cations did not effect ionic contents appreciably. It is concluded that these cations exert their effects on nerve or on muscle depending on the ligands of the ligands of the membrane bindingp these cations. Some of the cations bi-nd with the-SH group of the membrane and thus alter the transmembrane movement of Ca2+ bu the others do not. © 1980.
Type
journal article