title: Somatostatin lowers the cytosolic free Ca2+ concentration in clonal rat pituitary cells (GH3 cells).
abstract: Changes in the cytosolic free Ca2+ concentration, [Ca2+]i, have been proposed to mediate the regulation of the secretion of pituitary hormones by hypothalamic peptides. Using an intracellularly trapped fluorescent Ca2+ probe, quin2, [Ca2+]i was monitored in GH3 cells. Somatostatin lowers [Ca2+]i in a dose dependent manner from a prestimulatory level of 120 +/- 4 nM (SEM, n = 13) to 78 +/- 9 nM (n = 5) at 10(-7)M; the effect is half maximal at 2 X 10(-9) M somatostatin. The decrease in [Ca2+]i occurs rapidly after somatostatin addition and a lowered steady state [Ca2+]i is maintained for several minutes. Somatostatin does not inhibit the rapid rise in [Ca2+]i elicited by thyrotropin releasing hormone (TRH) and can still cause a decrease in [Ca2+]i in the presence of TRH (10(-7)M). Concomitantly with its action on [Ca2+]i somatostatin causes hyperpolarization of GH3 cells assessed with the fluorescent probe bis-oxonol. The lowering of [Ca2+]i by somatostatin is however not only due to reduced Ca2+ influx through voltage dependent Ca2+ channels, since it persists in the presence of the channel blocker verapamil. These results suggest that somatostatin may exert its inhibitory action on pituitary hormone secretion by decreasing [Ca2+]i.
mesh_terms: D000634:Aminoquinolines; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D005456:Fluorescent Dyes; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D010911:Pituitary Neoplasms / Q000503:physiopathology*; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D013004:Somatostatin / Q000494:pharmacology*; D013050:Spectrometry, Fluorescence; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology
chemical_list: D000634:Aminoquinolines; D005456:Fluorescent Dyes; D013004:Somatostatin; D013973:Thyrotropin-Releasing Hormone; C035739:Quin2; D011188:Potassium; D002118:Calcium