The Effect of Uncouplers of Oxidative Phosphorylation on Oxygen Uptake, Ubiquinone Redox Status and Energy‐Rich Phosphate Levels of Isolated Atria

Abstract

The effects of 2,4‐dinitrophenol and carbonyl‐cyanide‐m‐chlorophenylhydrazone on contractile amplitude and frequency, oxygen consumption, and ubiquinone redox status have been examined in spontaneously‐beating isolated guinea pig atria incubated with glucose. Dinitrophenol (2 to 100 μM) and carbonylcyanide‐chlorophenylhydrazone (0.02–0.4μM) lead to depression of contractile amplitude to 10% of control values accompanied by decreases in oxygen consumption of up to 20%. The ubiquinone redox status was shifted maximally from 32–35% oxidized ubiquinone to 66% by dinitrophenol and to 57% by carbonylcyanide‐chlorophenylhydrazone. The effect of dinitrophenol on oxygen consumption and ubiquinone redox status was further examined in non‐beating atria (low Ca++) incubated with glucose, malate or pyruvate. With glucose dinitrophenol led to a depression of oxygen consumption, while with malate or pyruvate a stimulation to 219% and 235% of the predrug level, respectively, was observed. At 100 μM dinitrophenol, ubiquinone redox status was shifted to the oxidized side and correlated with the rate of respiration with all three substrates. At lower concentrations of dinitrophenol, ubiquinone was oxidized to a lesser extent with malate while no significant shift was observed with pyruvate or glucose. Levels of creatine phosphate, ATP and pyruvate were decreased with increasing concentrations of dinitrophenol in non‐beating atria incubated with glucose and malate. No significant difference in these effects was detected with regard to substrate, although the trend indicated that the levels of these three compounds were more sensitive in atria incubated with glucose. Lactate levels were unaffected with low concentrations of dinitrophenol and elevated at 100 μM regardless of substrate. It was concluded that the effect of uncouplers of oxidative phosphorylation on ubiquinone redox status and oxygen consumption in intact atria is dependent upon contractile activity and exogenous substrate. However, the responses expected from studies with isolated mitochondria, namely, stimulation of oxygen uptake and ubiquinone oxidation over a range of dinitrophenol concentrations, can be obtained in non‐contractile atria incubated with malate. Copyright © 1970, Wiley Blackwell. All rights reserved