The kinetics of a non-inactivating K⁺ current in αT3-1 pituitary gonadotropes is not affected by holding potential

Abstract

The non-inactivating K⁺ currents in αT3-1, a gonadotroph cell line, were recorded in the presence of low intracellular free calcium concentration. The activation kinetics of the whole-cell currents and the gating charge measured from holding potential (V_HOLD) of -10 mV, V_HOLD=-80 mV in presence of 4-AP (4-aminopyridine), and V_HOLD=-10 mV with a hyperpolarizing prepulse to -80 mV were similar. No difference was observed in the onset of currents elicited from the hyperpolarizing potentials, suggesting deviation from the Cole-Moore prediction of increase in the delay of current onset with increasing hyperpolarization. The data suggests that the channel opens with at least one rate-limiting voltage-dependent step, which may imply that the position of the voltage sensor is unaffected by hyperpolarization.