Characterization of the calcium response to thyrotropin-releasing hormone in lactotrophs and GH cells

Thyrotropin-releasing hormone (TRH) acts via a G-protein-coupled receptor on lactotrophs to increase the intracellular free calcium ion concentration, [Ca2+](i). The [Ca2+](i) response depends on both TRH concentration and the duration of TRH exposure. An initial, short-lived [Ca2+](i) spike results from release of Ca2+ from intracellular stores, whereas a later sustained [Ca2+](i) increase, often characterized by [Ca2+](i) oscillations, results from an influx of extracellular Ca2+ through both voltage-gated and non-voltage-gated, store-operated Ca2+ channels. The initial spike phase predominates at high doses of TRH, whereas the plateau phase predominates at low doses. The mechanisms underlying the complex [Ca2+](i) response to TRH are discussed. (C) 1996, Elsevier Science Inc.