Diadenosine tetraphosphate-gating of recombinant pancreatic ATP-sensitive K+ channels

Diadenosine tetraphosphate (Ap4A) has been recently discovered in the pancreatic beta cells where targets ATP-sensitive K+ (K-ATP) channels, depolarizes the cell membrane and induces insulin secretion. However, whether Ap4A inhibit pancreatic K-ATP channels by targeting protein channel complex itself was unknown. Therefore, we coexpressed pancreatic K-ATP channel subunits, Kir6.2 and SUR1, in COS-7 cells and examined the effect of Ap4A on the single channel behavior using the inside-out configuration of the patch-clamp technique. Ap4A inhibited channel opening in a concentration-dependent manner. Analysis of single channels demonstrated that Ap4A did not change intraburst kinetic behavior of K-ATP channels, but rather decreased burst duration and increased between-burst duration. It is concluded that Ap4A antagonizes K-ATP channel opening by targeting channel subunits themselves and by keeping channels longer in closed interburst states.