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Journal of Cell Science, Vol 112, Issue 22 4143-4150, Copyright © 1999 by Company of Biologists

JOURNAL ARTICLES

The heterotrimeric Gi(3) protein acts in slow but not in fast exocytosis of rat melanotrophs

M Kreft, S Gasman, S Chasserot-Golaz, V Kuster, M Rupnik, SK Sikdar, M Bader and R Zorec
Laboratory of Neuroendocrinology-Molecular Cell Physiology, Institute of Pathophysiology, School of Medicine, P.O.B 2211, Slovenia.

Besides having a role in signal transduction some trimeric G-proteins may be involved in a late stage of exocytosis. Using immunocytochemistry and confocal microscopy we found that Gi(3)-protein resides mainly in the plasma membrane, whereas Gi(1/2-)protein is preferentially associated with secretory granules. To study the function of trimeric Gi(3)- and Gi(1/2)-proteins, secretory responses in single rat melanotrophs were monitored by patch-clamp membrane capacitance measurements. We report here that mastoparan, an activator of trimeric G-proteins, enhances calcium-induced secretory activity in rat melanotrophs. The introduction of synthetic peptides corresponding to the C-terminal domain of the (&agr;)-subunit of Gi(3)- and Gi(1/2)-proteins indicated that Gi(3 )peptide specifically blocked the mastoparan-stimulated secretory activity, which indicates an involvement of a trimeric Gi(3)-protein in mastoparan-stimulated secretory activity. Flash photolysis of caged Ca(2+)-elicited biphasic capacitance increases consisting of a fast and a slower component. Injection of anti-Gi(3) antibodies selectively inhibited the slow but not the fast component of secretory activity in rat melanotrophs. We propose that the plasma membrane-bound Gi(3)-protein may be involved in regulated secretion by specifically controlling the slower kinetic component of exocytosis.


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© The Company of Biologists Ltd 1999