Long-chain acyl-CoA esters and phosphatidylinositol phosphates modulate ATP inhibition of KATP channels by the same mechanism

Phosphatidylinositol phosphates (PIPs, e.g. PIP2) and long-chain acyl-CoA esters (e.g. oleoyl-CoA) are potent activators of K-ATP channels that are thought to link K-ATP channel activity to the cellular metabolism of PIPs and fatty acids. Here we show that the two types of lipid act by the same mechanism: oleoyl-CoA potently reduced the ATP sensitivity of cardiac (Kir6.2/SUR2A) and pancreatic (Kir6.2/SUR1) K-ATP channels in a way very similar to PIP2. Mutations (R54Q, R176A) in the C- and N-terminus of Kir6.2 that greatly reduced the PIP, modulation of ATP sensitivity likewise reduced the modulation by oleoyl-CoA, indicating that the two lipids interact with the same site. Polyvalent cations reduced the effect of oleoyl-CoA and PIP2 on the ATP sensitivity with similar potency suggesting that electrostatic interactions are of similar importance. However, experiments with differently charged inhibitory adenosine phosphates (ATP(4-), ADP(3-) and 2'(3')-O-(2,4,6-trinitrophenyl)adenosine 5'-monophosphate (TNP-AMP(2-))) and diadenosine tetraphosphate (Ap(4)A(5-)) ruled out a mechanism where oleoyl-CoA or PIP2 attenuate ATP inhibition by reducing ATP binding through electrostatic repulsion. Surprisingly, CoA (the head group of oleoyl-CoA) did not activate but inhibited K-ATP channels (IC50 = 265 +/- 33 mum). We provide evidence that CoA and diadenosine polyphosphates (e.g. Ap(4)A) are ligands of the inhibitory ATP-binding site on Kir6.2.