title: Caffeine stores and dopamine differentially require Ca(2+) channels in goldfish somatotropes.
abstract: 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 approximately 28% by 100 microM 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.
authors.affiliation: Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada.
authors.forename: C J
authors.initials: CJ
authors.lastname: Wong
authors.forename: J D
authors.initials: JD
authors.lastname: Johnson
authors.forename: W K
authors.initials: WK
authors.lastname: Yunker
authors.forename: J P
authors.initials: JP
authors.lastname: Chang
mesh_terms: D000818:Animals; D002104:Cadmium / Q000494:pharmacology; D002110:Caffeine / Q000494:pharmacology*; D002118:Calcium / Q000502:physiology; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D002478:Cells, Cultured; D002614:Chelating Agents / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004298:Dopamine / Q000494:pharmacology*; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D006054:Goldfish; D013006:Growth Hormone / Q000378:metabolism*; D007546:Isoquinolines / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D010903:Pituitary Gland, Anterior / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D017447:Receptors, Dopamine D1 / Q000502:physiology; D012433:Ryanodine / Q000494:pharmacology*; D013449:Sulfonamides
chemical_list: D015220:Calcium Channels; D002614:Chelating Agents; D004791:Enzyme Inhibitors; D007546:Isoquinolines; D017447:Receptors, Dopamine D1; D013449:Sulfonamides; D002104:Cadmium; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D012433:Ryanodine; D002110:Caffeine; D004533:Egtazic Acid; D013006:Growth Hormone; D017868:Cyclic AMP-Dependent Protein Kinases; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; C063509:N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide; D002118:Calcium; D004298:Dopamine