Inhibition of the Mitochondrial KATPChannel by Long-chain Acyl-CoA Esters and Activation by Guanine Nucleotides*

The mitochondrial KATPchannel (mitoKATP) is highly sensitive to ATP, which inhibits K+flux with K1/2 values of 20-40 μM. This raises the question, how can mitoKATPbe opened in the presence of physiological concentrations of ATP? We measured K+flux in liposomes reconstituted with purified mitoKATPand found that guanine nucleotides are potent activators of this channel. ATP-inhibited K+flux was completely reactivated by both GTP (K1/2 = 7 μM) and GDP (K1/2 = 140 μM). These ligands had no effect in the absence of ATP. The K1/2 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 mitoKATPwith K1/2 values of 260 nM and 80 nM, respectively. This inhibition was reversed by GTP (K1/2 = 232 μM) as well as by the K+channel openers cromakalim (20 μM) and diazoxide (10 μM). Inhibition of mitoKATPby 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 KATPchannel is determined by the relative cytosolic concentrations of GTP and long-chain acyl-CoA esters.