Characterization of calcium and sodium currents in porcine pars intermedia cells.

The whole-cell configuration of the patch-clamp technique was applied to porcine pars intermedia cells. A tetrodotoxin-sensitive sodium current was recorded. Three types of calcium current were observed. Depolarizations from a holding potential of 100 mV elicited a transient current (ICaT), whereas depolarizations from a holding potential of -40 mV evoked a sustained current (ICaS). A third current (ICaN; N for neither) was activated by strong depolarization to +10 or +20 mV from holding potentials of - 100 mV. Increasing internal Ca2+ significantly reduced the amplitude of ICaS.