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 AT P, 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 physiol ogical concentrations of ATP? We measured K+ flux in liposomes reconst ituted with purified mitoK(ATP) and found that guanine nucleotides are potent activators of this channel, ATP-inhibited K+ flux was complete ly 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], consist ent 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 i nhibition was reversed by GTP (K-1/2 = 232 mu M) as well as by the Kchannel openers cromakalim (20 mu M) and diazoxide (10 mu M). Inhibiti on of mitoK(ATP) by long-chain acyl-CoA eaters, like that of ATP, exhi bited an absolute requirement for Mg2+ ions. We propose that the open- closed state of the mitochondrial K-ATP channel is determined by the r elative cytosolic concentrations of GTP and long-chain acyl-CoA esters .