Gonadotropin-releasing hormone induces oscillatory membrane currents in rat gonadotropes

Electrophysiological studies were performed to characterize membrane currents of rat gonadotropes under basal conditions and after exposure to secretagogues. Gonadotropes were identified in primary cultures of rat anterior pituitaries by a reverse hemolytic plaque assay. Giga-seal patch clamp recording with the cell-attached configuration was used to monitor membrane currents in these cells. Spontaneous spikes in basal current were seen. These were blocked by methoxyverapamil and probably reflect Ca2+-dependent action potentials. Brief GnRH stimulation induced slow oscillatory changes in membrane current that evolved into a series of large amplitude inward pulses after about 8 min. Treatment with TRH had no effect, and depolarization with K+ led to delayed inward currents without any oscillatory behavior. Under conditions of Ca2+ channel blockade, GnRH stimulation did not induce pulses of inward current, but did lead to oscillatory activation of a small conductance ion channel apparently selective for K+. Taken together these results suggest that GnRH induces oscillations in intracellular Ca2+ and that these oscillations are controlled by biochemical processes.