TRANSMEMBRANE ION CURRENTS IN INSULIN-SEC RETING CLONAL RIN-5AH CELLS

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.