Me. Wisgirda et Se. Dryer, DIVALENT-CATIONS SELECTIVELY ALTER THE VOLTAGE-DEPENDENCE OF INACTIVATION OF A-CURRENTS IN CHICK AUTONOMIC NEURONS, Pflugers Archiv, 423(5-6), 1993, pp. 418-426
A-currents were studied in acutely dissociated chick autonomic neurons
. Switching from salines containing 4 mM Mg2+ to salines containing 4
mM Ca2+ caused a large positive shift in the voltage dependence of ste
ady-state inactivation, but had no effect on the voltage dependence or
kinetics of activation, deactivation, the rate at which channels beca
me inactivated, or the rate at which channels recovered from inactivat
ion. This effect saturated with increasing concentrations of Ca2+. Oth
er group IIA divalent cations were less effective than Ca2+, in the or
der Ca2+ > Ba2+ > Mg2+ = Sr2+. Application of 4 nM Mg2+ partially anta
gonized the effects of 4 mM Ca2+. The results suggest that divalent ca
tions selectively alter the voltage dependence of steady-state inactiv
ation by acting at sites accessible from the outside of the cell.