title: Modulation of Ca2+ oscillation and apamin-sensitive, Ca2+-activated K+ current in rat gonadotropes.
abstract: In rat pituitary gonadotropes, gonadotropin-releasing hormone (GnRH) stimulates rhythmic release of Ca2+ from stores sensitive to inositol 1,4,5-trisphosphate [Ins(1,4,5)P3], which in turn induces an oscillatory activation of apamin-sensitive Ca2+-activated K+ current, IK(Ca). Since GnRH also activates protein kinase C (PKC), we investigate the action of PKC while simultaneously measuring intracellular Ca2+ concentration ([Ca2+]i) and IK(Ca). Stimulation of PKC by application of phorbol 12-myristate 13-acetate (PMA) did not affect basal [Ca2+]i. However, PMA or phorbol 12,13-dibutyrate (PdBu), but not the inactive 4alpha-phorbol 12,13-didecanoate (4alpha-PDD), reduced the frequency of GnRH-induced [Ca2+]i oscillation and augmented the IK(Ca) induced by any given level of [Ca2+]i. The slowing of oscillations and the enhancement of IK(Ca) were mimicked by synthetic diacylglycerol (1,2-dioctanoyl-sn-glycerol) and could be induced during ongoing oscillations that had been initiated irreversibly in cells loaded with guanosine 5'-O-(3-thiotriphosphate) (GTP-[gammaS]). In contrast, when oscillations were initiated by loading cells with Ins(1,4,5)P3, phorbol esters enhanced IK(Ca) without affecting the frequency of oscillation. The protein kinase inhibitor, staurosporine, reduced IK(Ca) without affecting [Ca2+]i and partially reversed the phorbol-ester-induced slowing of oscillation. Therefore, activation of PKC has two rapid effects on gonadotropes. It slows [Ca2+]i oscillations probably by actions on phospholipase C, and it enhances IK(Ca) probably by a direct action on the channels.
mesh_terms: D000470:Alkaloids / Q000494:pharmacology; D000818:Animals; D001030:Apamin / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D004075:Diglycerides / Q000494:pharmacology; D004594:Electrophysiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007987:Gonadotropin-Releasing Hormone / Q000096:biosynthesis* / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques; D010703:Phorbol Esters / Q000494:pharmacology; D010902:Pituitary Gland / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D019311:Staurosporine; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors / Q000378:metabolism
chemical_list: D000470:Alkaloids; D004075:Diglycerides; D004791:Enzyme Inhibitors; D010703:Phorbol Esters; D015221:Potassium Channels; C044295:1,2-dioctanoylglycerol; D001030:Apamin; D007987:Gonadotropin-Releasing Hormone; D011493:Protein Kinase C; D010738:Type C Phospholipases; D019311:Staurosporine; D002118:Calcium