Inactivation of N-Type Calcium Current in Rat Sympathetic Neurons

Inactivation of N-type calcium current has been reported to be voltage dependent (Jones ＆ Marks, 1989) and $Ca^{2＋}$ dependent(Cox ＆ Dunlap, 1994). We examined inactivation by recording currents from the same cell both in [B $a^{2＋}$]$_{o}$ and [C $a^{2＋}$]$_{o}$ in rat sympathetic neurons. With 11 mM internal EGTA, fractional inactivation[l-(current amplitude at the end of 5 sec pulse/peak current amplitude [1-(current amplitude at the end of 5 sec pulse/peak current amplitude)] was larger in $Ca^{2+}$(0.80$\pm$0.07) than in $Ba^{2+}$(0.69$\pm$0.10)(n=31, p<0.001), but the current traces were nicely fitted with two exponential components both in $Ba^{2+}$ and $Ca^{2+}$.(omitted)ted)ted)