Novel, thapsigargin-insensitive intracellular Ca(2+) stores control growth hormone release from goldfish pituitary cells.
The relative contribution of intracellular Ca(2+) stores to basal and agonist-stimulated hormone release in pituitary cells is still not well understood, especially in non-mammalian vertebrates. Using ratiometric Ca(2+) imaging of single identified goldfish somatotropes, along with time-resolved measurements of growth hormone (GH) secretion, we investigated the Ca(2+)-dependent signal transduction of two endogenous regulators of GH release from the goldfish pituitary. Two gonadotropin-releasing hormones (sGnRH and cGnRH-II) initiated GH release in nominally Ca(2+) free conditions. GnRH-evoked GH release was additive to KCl-stimulated GH responses. Ca(2+) signals and GH release elicited by both GnRHs were abolished by pretreatment with TMB-8, which blocks the release of Ca(2+) from intracellular stores. GnRH-stimulated GH secretion is mediated by caffeine-sensitive intracellular Ca(2+) stores that are functionally independent from those sensitive to thapsigargin and other inhibitors of SERCA-type Ca(2+)/ATPases. The caffeine/TMB-8-sensitive Ca(2+) stores are also involved in spontaneous Ca(2+) signalling and the maintenance of prolonged GH release.
Johnson
J D
JD
Department of Biological Sciences, Biological Sciences Building, CW 405, University of Alberta, Alta, T6G 2E9, Edmonton, Canada.
Chang
J P
JP
D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020013:Calcium Signaling; D002478:Cells, Cultured; D005707:Gallic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D006054:Goldfish; D013006:Growth Hormone / Q000378:metabolism*; D007424:Intracellular Fluid / Q000378:metabolism; D008954:Models, Biological; D010902:Pituitary Gland / Q000166:cytology / Q000187:drug effects* / Q000502:physiology*; D019284:Thapsigargin / Q000494:pharmacology
D002121:Calcium Channel Blockers; D002110:Caffeine; C006014:8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate; D005707:Gallic Acid; D019284:Thapsigargin; D013006:Growth Hormone; D002118:Calcium