Pituitary cell type-specific electrical activity, calcium signaling and secretion
All secretory anterior pituitary cells exhibit spontaneous and extracellular calcium-dependent electrical activity, but differ with respect to the patterns of firing and associated calcium signaling and hormone secretion. Thus, somatotrophs and lactotrophs fire plateau-bursting action potentials spontaneously and without coupling to calcium release from intracellular stores, which generate calcium signals of sufficient amplitude to keep steady hormone release. In these cells, both spontaneous electrical activity and basal hormone secretion can be further amplified by activation of Gq/11 and Gs-coupled receptors and inhibited by Gi/o/z-coupled receptors. In contrast, gonadotrophs fire single, high-amplitude spikes with limited ability to promote calcium influx and exocytosis, whereas activated Gq/11-coupled receptors in these cells transform single-action potential spiking into the plateau-bursting type of electrical activity and trigger periodic high-amplitude calcium signals and exocytosis of prestored secretory vesicles. Here, we review biochemical and biophysical aspects of spontaneous and receptor-controlled electrical activity, calcium signaling, and hormone secretion in pituitary cells.