α‐Melanocyte‐stimulating hormone secretion from permeabilized intermediate lobe cells of rat pituitary gland The role of guanine nucleotides

Publisher Website
Google Scholar
Abstract
The non‐hydrolyzable GTP analogue, guanosine 5′‐O‐(3‐thiotriphosphate) (GTPγS) and cyclic AMP potentiated the Ca2+‐evoked secretion of α‐melanocyte‐stimulating hormone (α‐MSH) from permeabilized neurointermediate lobe (IL) cells of rat pituitary gland. The enhancement by Mg‐GTPγS (100 μM) and cyclic AMP (1 μM) depended on the intracellular CA2+ concentration (EC50 = 4.8 ± 1.8 and 4.6 ± 1.7 μM; mean ± SE, with and without Mg‐GTPγS 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‐GTPγS nor cyclic AMP alone was effective in potentiating α‐MSH secretion. GDPβS blocked the Mg‐GTPγS (100 μM) and cyclic AMP augmented secretion of α‐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‐GTPγS potentiation of α‐MSH secretion. These data suggest that the GTP‐binding protein may be involved in the regulation of α‐MSH secretion after Ca2+ entry into the cells, since the intracellular environment is controlled in the permeabilized cells.