Relationship of thyrotropin-releasing hormone-induced spike and plateau phases in cytosolic free Ca2+ concentrations to hormone secretion. Selective blockade using ionomycin and nifedipine.

In clonal rat pituitary cells (GH cells), thyrotropin-releasing hormone (TRH) induced a pattern of changes in cytosolic free calcium concentrations [( Ca2+]i) composed of two phases: an acute spike phase to micromolar levels which decayed (t1/2 = 8 s) to a near-basal concentration and then rose to a prolonged plateau phase of elevated [Ca2+]i (as measured using Quin 2). Closely following these cha…