ATP-SENSITIVE K+ CHANNEL IN THE MITOCHONDRIAL INNER MEMBRANE

MITOCHONDRIA take up and extrude various inorganic and organic ions, as well as larger substances such as proteins 1-4. The technique of patch clamping should provide real-time information on such transport and on energy transduction in oxidative phosphorylation. It has been applied to detect microscopic currents from mitochondrial membranes and conductances of ion channels in the 5-1,000 pS range in the outer and inner membranes 5-10. These pores are not, however, selective for particular ions. Here we use fused giant mitoplasts prepared from rat liver mitochondria to identify a small conductance channel highly selective for K+ in the inner mitochondrial membrane. This channel can be reversibly inactivated by ATP applied to the matrix side under inside-out patch configuration; it is also inhibited by 4-aminopyridine and by glybenclamide. The slope conductance of the unitary currents measured at negative membrane potentials was 9.7 +/- 1.0 pS (mean +/- s.d., n = 6) when the pipette solution contained 100 mM K+ and the bathing solution 33.3 mM K+. Our results indicate that mitochondria depolarize by generating a K+ conductance when ATP in the matrix is deficient.