Abstract
It was seen by the manometric technique that dihydroquinidine (DHQ) inhibits the oxygen consumption (QO2) and lowers the inorganic phosphorus esterif ication of mitochondria to the same level, with no uncoupling effect. It is possible to obtain proper mitochondria/DHQ ratios where no inhibition of both oxygen consumption and phosphorus esterif ication is observed. In this condition, an irradiation with visible light of wavelength longer than 320 m[mu] of the mitochondrial preparations suspended in 0.3 [image]_sucrose and successive manometric readings of the irradiated mitochondria suspended in a proper incubation medium containing alpha-ketoglutaric acid as substrate, show that visible light exerts an uncoupling action on oxidative phosphorylation (PO ratio). This property of DHQ seems independent of its typical toxic action and is produced only by the combination of the light with the drug. The data help to understand some of the electrocardiographs results previously observed by irradiating isolated and fatigued hearts of mammals perfused with diluted (10-4 [image] and more concentrated solutions (5x10-4 [image], 10-3_[image]) of DHQ. It is suggested that the damaging effect of the light and concentrated solutions of DHQ may involve the phosphorylative systems of the myocardial tissue, coupled with oxidation. The mechanism by which the light and more diluted solutions of DHQ improve and regularize the functioning of the fatigued isolated heart is unknown.

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