| Abstract: | Mechanism of tubocurarine (Tc) action on nonactive nicotinic acetylcholine receptors (NAChRs) of rat sympathetic neurons was studied by means of the patch-clamp whole-cell method. It was found that the blocking action of Tc on nonactive NAChRs augmented with the membrane hyperpolarization. The rate constant of Tc binding to nonactive NAChR (k + B) and the rate constant of dissociation of Tc-inactive NAChR complex (k-b) were found to be (9.0 +/- 1.5).10(3) M-1 s-1 and 0.11 +/- 0.05 s-1, respectively. Constant k + B decreased with the membrane depolarization (e-fold change in k + B corresponded to the potential shift approximately by 50 mV). In contrast, k-B slightly increased with the membrane depolarization (e-fold change in k-B corresponded to the potential shift approximately by 100 mV). It was concluded that Tc acted on the sympathetic neurons of rat noncompetitively as both open-channel and nonactive-receptor (closed-channel) blocker. |
