POSSIBLE INVOLVEMENT OF PROTEIN-PHOSPHORYLATION IN THE REGULATION OF THE SULFONYLUREA RECEPTOR OF A PANCREATIC BETA-CELL LINE, HIT-T15

The possible role of protein phosphorylation in modulation of [H-3]glibenclamide binding to the sulphonylurea receptor, a putative ATP-sensitive K-channel, was investigated in the cloned pancreatic beta-cell line, HIT T15. Diazoxide, an opener of ATP-sensitive K-channels, increased HIT cell Rb-86-efflux, inhibited insulin secretion and decreased non-competitively [H-3]glibenclamide binding to intact HIT cells. ATP-depletion reduced the [H-3]glibenclamide binding activity of intact cells but did not change diazoxide-insensitive binding. Although diazoxide alone did not change the binding of [H-3]glibenclamide to HIT cell membranes, the simultaneous presence of MgATP revealed an inhibition of [H-3]glibenclamide binding by diazoxide. This effect of MgATP was reproduced by MgATP-gamma-S, but not by MgADP, MgAMP-PNP or MgAMP-PCP. These findings suggest that protein phosphorylation may be involved in the response of ATP-sensitive K-channels to diazoxide.