title: Changes in cytosolic ionized calcium induced by activators of secretion in GH3 cells.
abstract: Cytosolic ionized calcium (Cai) was measured in GH3 cells with aequorin incorporated by hypoosmotic shock treatment. Cai rose from 0.4 to 1.3 microM after the administration of 10(-7) M thyrotropin-releasing hormone (TRH) and from 0.3 to 1.1 microM after depolarization caused by high-K concentration (60 mM). Repeated TRH stimulations decreased the magnitude of the Cai response. This magnitude was directly related to the interval between stimuli. Incubations in low-calcium media (0.13 mM Ca) for 0.5 h did not alter the Cai response to TRH, but incubations in Ca-free media reduced the response. These results suggest that TRH mobilized calcium from an endogenous pool of Ca that can be depleted and replenished. The rise in Cai induced by K depolarization was slower than that evoked by TRH (time constant, t = 9 s for TRH and t = 111 s for K depolarization). Even when Cai was elevated by K depolarization, it could still be further increased by TRH, suggesting that these two stimuli mobilize calcium from two different pools and by different mechanisms.
mesh_terms: D000331:Aequorin; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D010902:Pituitary Gland; D011188:Potassium / Q000494:pharmacology*; D013268:Stimulation, Chemical; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology*
chemical_list: D000331:Aequorin; D013973:Thyrotropin-Releasing Hormone; D011188:Potassium; D002118:Calcium