Dual effects of G-protein activation on Ca-dependent exocytosis in bovine lactotrophs.
The whole-cell patch-clamp technique was used to measure cell membrane capacitance (Cm) to monitor exocytosis in single-cultured bovine prolactin-secreting cells (lactotrophs) of the anterior pituitary. The cells were dialyzed with solutions containing different concentrations of ionised Ca and non-hydrolyzable GTP analogues (GTP-gamma-S and GMP-PNP) to activate G-proteins. We have identified two distinct effects of G-protein activation on Ca-induced exocytosis: (i) the maximum Cm increase due to intracellular Ca-dependent exocytosis was diminished, suggesting an inhibitory role of G-proteins close to the site of granule fusion, while (ii) the rate of Cm increase (delta Cm/delta t) was facilitated, revealing conversely a stimulatory role of G-proteins in the translocation of secretory granules to the fusion sites.
Sikdar
S K
SK
Department of Neuroendocrinology, AFRC Institute of Animal Physiology & Genetics Research, Babraham, Cambridge, England.
Zorec
R
R
Brown
D
D
Mason
W T
WT
D000818:Animals; D002118:Calcium / Q000502:physiology*; D002417:Cattle; D004789:Enzyme Activation / Q000187:drug effects; D005089:Exocytosis / Q000187:drug effects; D019204:GTP-Binding Proteins / Q000502:physiology*; D006150:Guanine Nucleotides / Q000494:pharmacology; D066298:In Vitro Techniques; D010903:Pituitary Gland, Anterior / Q000378:metabolism*; D011388:Prolactin / Q000378:metabolism*
D006150:Guanine Nucleotides; D011388:Prolactin; D019204:GTP-Binding Proteins; D002118:Calcium