Action potentials occur in cells of the normal anterior pituitary gland and are stimulated by the hypophysiotropic peptide thyrotropin-releasing hormone.

Abstract

Electrical activity in the form of action potentials (spikes) was discovered in normal anterior pituitary cells obtained from rats by tissue dissociation and maintained in culture. Passage of outward current through the microsuction electrodes used for recording often increased spike frequency in spontaneously active cells or initiated spikes in cells previously electrically silent. Spiking persisted in the presence of tetrodotoxin and in the absence of Na, but was inhibited by the calcium blockers D600 and La. Such spikes appear to be Ca spikes, but contributions to spiking by other ions are not excluded. The stimulant hypophysiotropic peptide thyrotropin-releasing hormone elicited spiking in about 10% of the cells on which it was tested. These cells are possibly thyrotrophs and mammotrophs, the physiological target cells for this hormone. These results, considered along with existing evidence that adenohypophyseal secretion requires Ca and is elicited by calcium ionophores, prompt the conclusion that action potentials involving Ca influx participate in stimulus-secretion coupling in the anterior pituitary. It may be by stimulating or modulating such electrical activity (with hypophysiotropic hormones) that the brain regulates anterior pituitary secretion.