The whole-cell configuration of patch-clamp technique has been applied
to insulin-secreting RIN-5AH cells. The mean resting potential was -6
3 mV. Depolarizing voltage steps from the holding potential -70 mV act
ivated a transient inward current followed by a delayed outward one. T
he outward currents were supressed by substituting Cs+ for K+ in the p
ipette solution and blocked by extracellularly applied tetraethylammon
ium and 4-aminopyridine. These data suggest the outward current to rep
resent a delayed potassium conductance. The inward currents were ident
ified as carried by both Ca2+ and Na+ ions because they were blocked b
y extracellularly applied Cd2+, Ni2+ and tetrodotoxin. The two ion com
ponents of the inward current could be separated, using Ca2+-free and
Na-free bath solutions. Experiments with consecutive applications of c
alcium and sodium channel blockers revealed that Na+ and Ca2+ currents
are mediated through different ion channels.