Identification of anion and cation pathways in the inner mitochondrial membrane by patch clamping of mouse liver mitoplasts.

Alkalinization of the matrix side of the mitochondrial inner membrane by pH shifts from 6.8 to 8.3 caused a reversible increase in current of 3.2 +/- 0.2 pA (mean +/- SE, n = 21) at +/- 40 mV measured using patch-clamp techniques. The current increase was reversed in a graded fashion by the addition of Mg2+ as well as a reduction in pH. Detection of single-channel events was done at 0.5, 1 and 2 M KCl. The single-channel amplitude in 0.15 M KCl corresponds to approximately 15 pS. Reversal potentials derived from whole patch currents indicated that the inner mitochondrial membrane was primarily cation selective at pH 6.8 with a PK/PCl = 32 (n = 6). Treatment with alkaline pH (8.3) increased the current and anion permeability (PK/PCl = 16, n = 6). The membrane becomes completely cation selective when low concentrations (12 microM) of the drug propranolol are added. The amphiphilic drugs amiodarone (4 microM), propranolol (70 microM) and quinine (0.6 mM) blocked almost all of the current. The pH-dependent current was also inhibited by tributyltin. These results are consistent with the presence of two pathways in the inner mitochondrial membrane. One is cation selective and generally open and the other is anion selective and induced by alkaline pH. The alkaline pH-activated channel likely corresponds to the inner membrane anion channel postulated by others from suspension studies.