The heterotrimeric Gi(3) protein acts in slow but not in fast exocytosis of rat melanotrophs.
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.
Kreft
M
M
Laboratory of Neuroendocrinology-Molecular Cell Physiology, Institute of Pathophysiology, School of Medicine, P.O.B 2211, Slovenia.
Gasman
S
S
Chasserot-Golaz
S
S
Kuster
V
V
Rupnik
M
M
Sikdar
S K
SK
Bader
M
M
Zorec
R
R
D000818:Animals; D000906:Antibodies / Q000276:immunology / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D004553:Electric Conductivity; D005089:Exocytosis / Q000187:drug effects / Q000502:physiology*; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000276:immunology / Q000494:pharmacology / Q000502:physiology*; D036341:Intercellular Signaling Peptides and Proteins; D008856:Microscopy, Fluorescence; D010455:Peptides; D010902:Pituitary Gland / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D014862:Wasp Venoms / Q000494:pharmacology
D000906:Antibodies; D036341:Intercellular Signaling Peptides and Proteins; D010455:Peptides; D014862:Wasp Venoms; C037500:mastoparan; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D002118:Calcium