Patch clamp analysis of a partially purified ion channel from rat liver mitochondria

A protein fraction isolated from detergent-solubilized mitochondrial membranes by affinity chromatography on immobilized quinine was reconstituted into phospholipid vesicles by detergent dialysis. Vesicles were fused to a diameter of 10 microns or larger by dehydration and rehydration. Patch clamp recordings carried out in detached mode with a symmetrical solution of 150 mM KCl, 5 mM HEPES, and 0.1 mM CaCl2 revealed conductance increments of 140 pS. Transitions of 40 pS were less frequently observed. Control vesicles which lacked protein showed no channel activity. The probability for the 140 pS channel to be open increased with increasing voltage in the range from 20 to 80 mV (positive potentials relative to what was the vesicle interior prior to excision), while the single channel conductance remained essentially constant. The 140 pS channel did not open at negative voltages. The voltage dependence suggests asymmetric incorporation of the 140 pS channel into vesicle membranes during reconstitution.