Caffeine stores and dopamine differentially require Ca2+ channels in goldfish somatotropes

• Published in: American journal of physiology. Regulatory, integrative and comparative physiology integrative and comparative physiology, 2001-02, Vol.280 (2), p.494
• Main Authors: Wong, Calvin J. H, Johnson, James D, Yunker, Warren K, Chang, John P
• Format: Article
• Language: English
• ISSN: 0363-6119; 1522-1490
• DOI: 10.1152/ajpregu.2001.280.2.R494

Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada The regulation of growth hormone (GH) secretion by intracellular Ca 2+ stores was studied in dissociated goldfish somatotropes. We characterized a caffeine-activated intracellular store that had been shown to mediate GH release in response to gonadotropin-releasing hormone. The peak response of caffeine stimulation was reduced by ~28% by 100 µM ryanodine in a use-dependent manner suggesting that the first 10 min of GH release is partially mediated by a caffeine-activated ryanodine receptor. The temporal sensitivities of caffeine- and dopamine-evoked GH release to blockade of Cd 2+ -sensitive Ca 2+ channels were compared. We demonstrated that the initial phase of dopamine-evoked release was dependent on Ca 2+ channels, whereas the initial phase of caffeine-evoked release was sensitive only to pretreatment blockade. This would suggest that the maintenance of one class of caffeine-activated intracellular stores requires entry of Ca 2+ through Cd 2+ -sensitive Ca 2+ channels. This differential temporal requirement for Ca 2+ channels in Ca 2+ signaling may be a mechanism to segregate intracellular signaling pathways of multiple neuroendocrine regulators in the teleost pituitary. calcium-induced calcium release; adenosine 3',5'-cyclic monophosphate; growth hormone; pituitary; secretion * C. J. H. Wong and J. D. Johnson contributed equally to this work.