Alpha-melanocyte-stimulating hormone secretion from permeabilized intermediate lobe cells of rat pituitary gland. The role of guanine nucleotides.
The non-hydrolyzable GTP analogue, guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) and cyclic AMP potentiated the Ca2+-evoked secretion of alpha-melanocyte-stimulating hormone (alpha-MSH) from permeabilized neurointermediate lobe (IL) cells of rat pituitary gland. The enhancement by Mg-GTP gamma S (100 microM) and cyclic AMP (1 microM) depended on the intracellular Ca2+ concentration (EC50 = 4.8 +/- 1.8 and 4.6 +/- 1.7 microM; mean +/- SE, with and without Mg-GTP gamma S and cyclic AMP, respectively). A similar effect was observed with guanine nucleotide triphosphate (GTP and GppNHp). Mg was absolutely required for this event. Neither Mg-GTP gamma S nor cyclic AMP alone was effective in potentiating alpha-MSH secretion. GDP beta S blocked the Mg-GTP gamma S (100 microM) and cyclic AMP augmented secretion of alpha-MSH. Neither neomycin (which affects the process of inositol 1,4,5-triphosphate-mediated Ca2+ mobilization) or colchicine (which influences microtubule assembly) had an effect on the cyclic AMP and Mg-GTP gamma S potentiation of alpha-MSH secretion. These data suggest that the GTP-binding protein may be involved in the regulation of alpha-MSH secretion after Ca2+ entry into the cells, since the intracellular environment is controlled in the permeabilized cells.
D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002463:Cell Membrane Permeability / Q000187:drug effects*; D002478:Cells, Cultured; D003078:Colchicine / Q000494:pharmacology; D006150:Guanine Nucleotides / Q000494:pharmacology*; D006160:Guanosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D009074:Melanocyte-Stimulating Hormones / Q000378:metabolism*; D009355:Neomycin / Q000494:pharmacology; D010904:Pituitary Gland, Posterior / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D012265:Ribonucleotides / Q000494:pharmacology
D006150:Guanine Nucleotides; D012265:Ribonucleotides; D006160:Guanosine Triphosphate; D009074:Melanocyte-Stimulating Hormones; D009355:Neomycin; D008274:Magnesium; D003078:Colchicine; D002118:Calcium