Rhythmic exocytosis stimulated by GnRH-induced calcium oscillations in rat gonadotropes.
In pituitary gonadotropes, gonadotropin-releasing hormone (GnRH) induces the rhythmic release of Ca2+ from an inositol 1,4,5-trisphosphate (IP3)-sensitive store. Simultaneous measurement of the concentration of cytosolic free Ca2+ ([Ca2+]i) and exocytosis in single identified gonadotropes showed that each elevation of [Ca2+]i induced a burst of exocytosis. These phenomena were largely suppressed by buffering of [Ca2+]i but persisted in the absence of extracellular Ca2+. Activation of voltage-gated Ca2+ channels by brief depolarizations seldom supplied enough Ca2+ for exocytosis, but [Ca2+]i elevations induced by photolysis of caged IP3 did trigger exocytosis, confirming that GnRH-stimulated gonadotropic hormone secretion is closely coupled to intracellular Ca2+ release. Agonist-induced oscillations of [Ca2+]i in secretory cells may be a mechanism to optimize the secretory output while avoiding the toxic effects of sustained elevation of [Ca2+]i.
Department of Physiology and Biophysics, University of Washington School of Medicine, Seattle 98195.
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Almers
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Hille
D000200:Action Potentials; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology; D003594:Cytoplasmic Granules / Q000187:drug effects / Q000502:physiology; D004594:Electrophysiology; D005089:Exocytosis / Q000187:drug effects*; D007987:Gonadotropin-Releasing Hormone / Q000008:administration & dosage / Q000494:pharmacology*; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology; D008297:Male; D010507:Periodicity; D010782:Photolysis; D010902:Pituitary Gland / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D051381:Rats; D017207:Rats, Sprague-Dawley
D015220:Calcium Channels; D007987:Gonadotropin-Releasing Hormone; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium