Molecular Pharmacology, Vol 7, 199-208, Copyright © 1971 by the American Society for Pharmacology and Experimental Therapeutics

Phosphatase and Ouabain-Sensitive Adenosine Triphosphatase Activities of the Perfused Frog Heart

¹ Departments of Medicine, Biochemistry, and Pharmacology, University of Southern California School of Medicine, Los Angeles, California 90033

An ATPase and p-nitrophenyl phosphatase activity has been characterized in the perfused frog ventricle. Addition of ATP and p-nitrophenyl phosphate to the perfusate results in their rapid hydrolysis upon contact with the ventricle. A spectrophotometric system was developed to monitor the perfusate continuously to determine the hydrolytic activity of the ventricle while also monitoring contraction. Ouabain at 3 µM significantly inhibits the ATPase durin the positive inotropic actions of the drug. This inhibition progressively increases as inotropism proceeds toward toxicity. Ten-fold higher concentrations of ouabain (30 µM) do not inhibit the p-nitrophenyl phosphatase. ATP increases the toxicity of digoxin and its binding to the ventricles. It is proposed that the ATPase activity of the ventricle might be associated with the (Na⁺ + K⁺)-dependent ATPase enzyme system

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ACKNOWLEDGMENTS The technical assistance of Sharon Laws, who helped with some of these experiments, and the secretarial assistance of Georgene Denison is gratefully acknowledged. Special thanks are due to Dr. Charles Mayo, Dean of the Graduate School, and Dr. Franz Bauer, Dean of the Medical School, who provided funds essential for this work. It is a pleasure to acknowledge the counsel of Drs. Roger Jelliffe and David H. Blankenhorn.