The mitochondrial K(ATP), channel (mitoK(ATP)) is highly sensitive to ATP, which inhibits K+ flux with K( 1/4 ) values of 20-40 μM. 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( 1/4 ) = 7 μM) and GDP (K( 1/4 ) = 140 μM). These ligands had no effect in the absence of ATP. The K( 1/4 ) 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( 1/4 ) values of 260 nM and 80 nM, respectively. This inhibition was reversed by GTP (K( 1/4 ) = 232 μM) as well as by the K+ channel openers cromakalim (20 μM) and diazoxide (10 μM). 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.
ASJC Scopus subject areas