Stimulation of Ca(2+)-independent exocytosis in rat pituitary gonadotrophs by G-protein.
We employed the whole-cell recording technique in conjunction with fluorometry to measure cytosolic Ca(2+) concentration ([Ca(2+)](i)) and exocytosis (capacitance measurement) in single, identified rat gonadotrophs. Direct activation of G-protein (via intracellular dialysis of non-hydrolysable analogues of GTP, but not of GDP) triggered a slow rise in capacitance even in the presence of a fast intracellular Ca(2+) chelator. The broad-spectrum kinase inhibitors H7 and staurosporine did not prevent this Ca(2+)-independent exocytosis, ruling out the involvement of the cAMP and PKC pathways. AlF(4)(-), a potent stimulator of heterotrimeric G-proteins, failed to stimulate any exocytosis when the intracellular Ca(2+) store was depleted, implicating the involvement of AlF(4)(-)-insensitive G-protein(s). Maximal stimulation of Ca(2+)-independent exocytosis by GTP analogues did not reduce the number of readily releasable granules that were available subsequently for Ca(2+)-dependent release. The last finding raises the possibility that the G-protein-stimulated Ca(2+)-independent exocytosis may regulate a pool of granules that is distinct from the Ca(2+)-dependent pool.
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Department of Pharmacology, University of Alberta, Edmonton, Alberta, Canada T6G 2H7. fred.tse@ualberta.ca
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D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine / Q000494:pharmacology; D017607:Aluminum Compounds / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D000242:Cyclic AMP / Q000378:metabolism; D003594:Cytoplasmic Granules / Q000187:drug effects / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D004533:Egtazic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005089:Exocytosis / Q000187:drug effects / Q000502:physiology*; D005459:Fluorides / Q000494:pharmacology; D005470:Fluorometry; D019204:GTP-Binding Proteins / Q000378:metabolism* / Q000494:pharmacology; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology; D008297:Male; D018408:Patch-Clamp Techniques; D010782:Photolysis; D010903:Pituitary Gland, Anterior / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D051381:Rats; D019311:Staurosporine / Q000494:pharmacology
D017607:Aluminum Compounds; D004791:Enzyme Inhibitors; C050992:tetrafluoroaluminate; D006165:Guanylyl Imidodiphosphate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D004533:Egtazic Acid; D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D000242:Cyclic AMP; D011493:Protein Kinase C; D019204:GTP-Binding Proteins; D000252:Calcium-Transporting ATPases; D019311:Staurosporine; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D005459:Fluorides; D002118:Calcium