Membrane Phosphoinositides Control Insulin Secretion Through Their Effects on ATP-Sensitive K⁺ Channel Activity

Abstract

ATP-sensitive K⁺ channels (K_ATP channels) of pancreatic β-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 β-cells. Here, we tested this hypothesis by manipulating the interactions between K_ATP channels and membrane phospholipids in a β-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 PIP₂ levels via overexpression of a lipid kinase, phosphatidylinositol 4-phosphate 5 kinase, decreases the ATP sensitivity of endogenous K_ATP channels by ∼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.