ATP Modulates Interaction of Syntaxin-1A with Sulfonylurea Receptor 1 to Regulate Pancreatic β-Cell KATP Channels

ATP-sensitive potassium (K-ATP) channels are regulated by a variety of cytosolic factors (adenine nucleotides, Mg2+, phospholipids, and pH). We previously reported that K-ATP channels are also regulated by endogenous membrane-bound SNARE protein syntaxin-1A (Syn-1A), which binds both nucleotide-binding folds of sulfonylurea receptor (SUR) 1 and 2A, causing inhibition of K-ATP channel activity in pancreatic islet beta-cells and cardiac myocytes, respectively. In this study, we show that ATP dose-dependently inhibits Syn-1A binding to SUR1 at physiological concentrations, with the addition of Mg2+ causing a decrease in the ATP-induced inhibitory effect. This ATP disruption of Syn-1A binding to SUR1 was confirmed by FRET analysis in living HEK293 cells. Electrophysiological studies in pancreatic beta-cells demonstrated that reduced ATP concentrations increased K-ATP channel sensitivity to Syn-1A inhibition. Depletion of endogenous Syn-1A in insulinoma cells by botulinum neurotoxin C1 proteolysis followed by rescue with exogenous Syn-1A showed that Syn-1A modulates K-ATP channel sensitivity to ATP. Thus, our data indicate that although both ATP and Syn-1A independently inhibit beta-cell K-ATP channel gating, they could also influence the sensitivity of K-ATP channels to each other. These findings provide new insight into an alternate mechanism by which ATP regulates pancreatic beta-cell K-ATP channel activity, not only by its direct actions on Kir6.2 pore subunit, but also via ATP modulation of Syn-1A binding to SUR1.