Luteinizing Hormone Inhibits Potassium Outward Currents in Swine Granulosa Cells by Intracellular Calcium Mobilization*

Potassium currents of swine granulosa cells were studied using the patch clamp technique in the whole cell configuration. Granulosa cells stepped to positive potentials (+60 mV) from -40 mV holding potential exhibit a slowly activating, noninactivating outward potassium current. Tail current reverse potential (between -90 and -100 mV) and the current inhibition brought about by the replacement of KCl with CsCl in the pipette solution indicate that this current is carried by K ions. LH was found to significantly reduce the amplitude of this current. The effect was dose and time dependent. Similar inhibition (20-30% of the initial current) was reached with doses of 1-50 micrograms/ml, but in times proportionally shorter as the dose increased (50% inhibition was reached in 170-180 and 30-40 sec with 1 and 50 micrograms LH/ml, respectively). Much longer and variable times (3-10 min) were required with lower doses (0.2 microgram/ml). The effect of LH was independent of extracellular Ca, while preexposure of cells to TMB-8, an inhibitor of intracellular Ca mobilization, completely prevented the effect of LH. Outward currents after LH treatment could be completely restored by perfusing the cells with ionomycin in Ca-free medium to facilitate calcium efflux from the cells. The present studies indicate that LH modifies the bioelectrical properties of swine granulosa cells. This effect is mediated by an elevation of intracellular calcium, probably mobilized from intracellular stores. The induced changes in K conductance may play a specific role in the transduction mechanisms for LH.