Stimulation of Ca2+-independent exocytosis in rat pituitary gonadotrophs by G-protein

1. We employed the whole-cell recording technique in conjunction with fluor ometry to measure cytosolic Ca2+ concentration ([Ca2+],) and exocytosis (ca pacitance measurement) in single, identified rat gonadotrophs. 2. Direct activation of G-protein (via intracellular dialysis of non-hydrol ysable analogues of GTP, but not of GDP) triggered a slow rise in capacitan ce even in the presence of a fast intracellular Ca2+ chelator. 3. The head-spectrum kinase inhibitors H7 and staurosporine did not prevent this Ca2+- independent exocytosis, ruling out the involvement of the cAMP and PKC pathways. 4. AIF(4)(-); a potent stimulator of heterotrimeric G-proteins, failed to s timulate any exocytosis when the intracellular Ca2+ store was depleted, imp licating the involvement of AIF(4)(-)- insensitive G-protein(s). 5. Maximal stimulation of Ca2+-independent exocytosis by GTP analogues did not reduce the number of readily releasable granules that were available su bsequently for Ca2+-dependent release. 6. The last finding raises the possibility that the G-protein-stimulated Ca 2+-independent exocytosis may regulate a pool of granules that is distinct fr om the Ca2+-dependent pool.