Action of propranolol on mitochondrial functions—effects on energized ion fluxes in the presence of valinomycin

The effects of propranolol on mitochondrial ion fluxes have been studied in oscillatory conditions in the presence of potassium plus valinomycin. The drug was able to decrease slightly the rate of swelling and that of passive contraction a little more. When the concentration of external salt was below 10 mM, propranolol decreased the extent of swelling; above 15 mM it was increased by the drug. The inhibition of contraction was abolished by nigericin or raised pH and was less evident with ATP rather than succinate as the source of energy. Propranolol only slightly affected the oxidative phosphorylation and latent ATPase activity of mitochondria. At low concentrations of salts the rate of valinomycin-stimulated respiration and ATPase activity were both inhibited. At higher concentrations of the salts, both were stimulated. It is suggested that the stimulation of respiration and ATPase activity result from increased ion uptake. Propranolol seems to stabilize an “energized” state, possibly by inhibiting the entry of protons, thereby retarding the equilibration of ionic gradients across the inner membrane.