INWARD MEMBRANE CURRENTS AND ELECTROPHYSIOLOGICAL RESPONSES TO GNRH IN OVINE GONADOTROPES

Abstract

We have used conventional whole-cell patch-clamp to investigate the membrane currents of ovine anterior pituitary gonadotropes, and nystatin-perforated whole-cell patch-clamp to record the membrane potential changes elicited by the natural hypothalamic secretagogue, gonadotropin-releasing hormone (GnRH). A large basal inward current found by voltage clamp was blocked by tetrodotoxin (TTX) (ED50 < 10 nM), identifying it as a Na+ current. Slowly inactivating inward current, activated at potentials more positive than -30 mV, remained in Na(+)-free medium or in the presence of 1 microM TTX. This current was abolished by ionic Ca2+ channel blockade. In the presence of nifedipine about 70% of this..