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Influence of K ATP channel openers on the permeability of cardiac mitochondrial membranes for potassium ions, protons and ADP during mild acidosis

+ flux to the mitochondrial matrix was registered spectropho- tometrically as the swelling of non-respiring mitochondria at 540 nm in the KNO 3 and NH 4 NO 3 medium. The apparent K M for ADP of mitochondria was estimated from the least-squares fit to the Michaelis-Menten equation. The results showed that the K ATP channel openers diazoxide and pinacidil could activate potassium ion and proton flux to the mitochondrial matrix both under normal (pH 7.4) and mildly acidic (pH 6.8) conditions. Mild acidosis incre- ased the apparent K M for ADP of mitochondria two times (up to 60.6 ± 3.4 μM) as compared to control (33.0 ± 3.2 μM). The K ATP channel opener diazoxide (100 μM) increased the apparent K M for ADP by 40% under control and by 30% under mildly acidic conditions. Our results suggest that K ATP channel openers could suppress the ADP/ATP exchange during ischemia and thus promote preservation of ATP in cardiomyocyte s.