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 PIP₂ 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 (Ap₄A^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 μM). We provide evidence that CoA and diadenosine polyphosphates (e.g. Ap₄A) are ligands of the inhibitory ATP-binding site on Kir6.2.