EFFECTS OF QUINIDINE AND PROPRANOLOL ON ENERGY TRANSDUCTION IN BEEF-HEART MITOCHONDRIA

The effects of quinidine and propranolol on mitochondrial respiration and on three respiration-dependent functions (oxidative phosphorylation, calcium uptake, and uncoupler-stimulated respiration) were studied. Both quinidine and propranolol inhibited respiration and three respiration-dependent functions in the presence of pyruvate plus malate or succinate plus rotenone as the substrates. Furthermore, both quinidine and propranolol inhibited ATP-Pi exchange, a mitochondrial energy-coupling reaction that does not involve respiration. Inhibition by propranolol but not by quinidine was strongly depended on the KCl concentration of the medium, the inhibition being maximal at low concentrations. The effect of KCl appears to lower the affinity of propranolol to the mitochondrial membrane. © 1979.