Membrane phosphoinositides control insulin secretion through their effects on ATP-sensitive K+ channel activity

ATP-sensitive K+ channels (K-ATP channels) of pancreatic beta-cells play key roles in glucose-stimulated insulin secretion by linking metabolic signals to cell excitability. Membrane phosphoinositides, in particular phosphatidylinositol 4,5-bisphosphates (PIP2), stimulate K-ATP channels and decrease channel sensitivity to ATP inhibition; as such, they have been postulated as critical regulators of K-ATP channels and hence of insulin secretion in beta-cells. Here, we tested this hypothesis by manipulating the interactions between K-ATP channels and membrane phospholipids in a beta-cell line, INS-1, and assessing how the manipulations affect membrane excitability and insulin secretion. We demonstrate that disruption of channel interactions with PIP2 by overexpressing PIP2-insensitive channel subunits leads to membrane depolarization and elevated basal level insulin secretion at low glucose concentrations. By contrast, facilitation of channel interactions with PIP2 by upregulating PlP(2) levels via overexpression of a lipid kinase, phosphatidylinositol 4-phosphate 5 kinase, decreases the ATP sensitivity of endogenous K-ATP channels by similar to 26-fold and renders INS-1 cells hyperpolarized, unable to secrete insulin properly in the face of high glucose. Our results establish an important role of the interaction between membrane phosphoinositides and K-ATP channels in regulating insulin secretion.