Actions of zinc on rapidly inactivating A-type and non-inactivating M-type potassium currents in bullfrog sympathetic neurons

The actions of zinc on A-type potassium current (I(A)) were studied in dissociated bullfrog sympathetic neurons. Zinc (1-300 microM) caused a parallel shift in the activation and inactivation curves to a depolarizing direction, thereby enhancing I(A) around physiological resting potential. An EC50 value was 70-100 microM for these actions. The zinc actions were non-selective in a sense that zinc inhibited M-type potassium current (I(M)) with an IC50 value of 300 microM. Zinc was without effect on the maximum conductance for I(A) and the kinetic behavior for I(M). The ability of low concentrations of zinc to modulate separate set of potassium currents such as I(A) and I(M) in conceptually distinct manner may therefore assume pathophysiological importance for autonomic neurons.