Decreased ADP-ribosylation of the G alpha(olf) and G alpha(s) subunits by high glucose in pancreatic B-cells

In HIT-T15 insulinoma B-cells incubated in presence of [P-32]NAD, we identi fied by autoradiography and immunoblotting ADP-ribosylation (ADP-R) of the trimeric G-protein G alpha(s) and G alpha(olf) subunits (45 kDa) induced by cholera toxin in M1 (120,000g) and M2 (70,000g) subcellular fractions cont aining plasma membranes, insulin granules, and mitochondria. This ADP-R ind icates that these two fractions contain functionally competent G alpha subu nits for adenylyl cyclase activation. Prolonged exposure of HIT-T15 cells t o high glucose (25 mM instead of 6 mM) specifically reduced the ADP-R in G alpha(s) and G alpha(olf) subunits in the M1 fraction only, despite the cle ar increase of their accumulation in this compartment. A similar alteration in the ADP-R of the M1-associated G alpha(s) and G alpha(olf) subunits was observed in pancreatic islets isolated from fasted and fed rats. These res ults may explain, at least in part, the undesirable effects of sustained hy perglycemia on the cAMP-dependent process of insulin secretion in diabetes. (C) 2000 Academic Press.