Inhibition of the mitochondrial K-ATP channel by long-chain Acyl-CoA esters and activation by guanine nucleotides

The mitochondrial K-ATP channel (mitoK(ATP)) is highly sensitive to ATP, which inhibits K+ flux with K-1/2 values of 20-40 mu M. This raises the question, how can mitoK(ATP) be opened in the presence of physiological concentrations of ATP? We measured K+ flux in liposomes reconstituted with purified mitoK(ATP) and found that guanine nucleotides are potent activators of this channel, ATP-inhibited K+ flux was completely reactivated by both GTP (K-1/2 = 7 mu M) and GDP (K-1/2 = 140 mu M). These ligands had no effect in the absence of ATP, The K-1/2 for ATP inhibition exhibited quadratic dependence on [GTP] and [GDP], consistent with two binding sites for guanine nucleotides. We also found that palmitoyl-CoA and oleoyl-CoA inhibited K+ flux through reconstituted mitoK(ATP) with K-1/2 values of 260 nM and 80 nM, respectively. This inhibition was reversed by GTP (K-1/2 = 232 mu M) as well as by the K+ channel openers cromakalim (20 mu M) and diazoxide (10 mu M). Inhibition of mitoK(ATP) by long-chain acyl-CoA esters, like that of ATP, exhibited an absolute requirement for Mg2+ ions. We propose that the open-closed state of the mitochondrial K-ATP channel is determined by the relative cytosolic concentrations of GTP and long-chain acyl-CoA esters.