IDENTIFICATION OF G PROTEIN ALPHA-SUBUNITS IN RINM5F CELLS AND THEIR SELECTIVE INTERACTION WITH GALANIN RECEPTOR

Galanin, an inhibitor of insulin secretion in pancreatic beta-cells, exerts its multiple effects through mechanisms that are sensitive to pertussis toxin (PTX). G proteins have been characterized in RINm5F cells. By ADP ribosylation and immunoblotting, the alpha-subunits of G(i1), G(i2), G(i3), and two forms of G(o) were identified, G(i-alpha-2) being predominant. As expected from a G protein-linked receptor, GTP and its nonhydrolyzable analogue GTP-gamma-S decreased tracer galanin binding to cell membranes. This resulted from a change in receptor affinity without any modification in the number of sites. Selective antibodies against the COOH-terminal decapeptide of the alpha-subunits of the G(i) and G(o) proteins were used to block G protein interaction before we studied galanin binding. Antibody AS, which selectively recognizes G(i-alpha-1), and G(i-alpha-2), decreased tracer galanin binding to membranes at concentrations where there were no effects of other antibodies specifically directed against G(i-alpha-3) or G-alpha-o. These data suggest that G(i1) and/or G(i2) interact with the galanin receptor and probably mediate the effects of galanin in pancreatic beta-cells.