Molecular Pharmacology, Vol 14, 122-129, Copyright © 1978 by the American Society for Pharmacology and Experimental Therapeutics

Specific [³H]Ouabain Binding to Rat Heart and Skeletal Muscle: Effects of Thyroidectomy

¹ Department of Pharmacology and Toxicology, University of Rochester School of Medicine and Dentistry, Rochester, New York 14642

Administration of triiodothyronine increased specific [³H]ouabain binding by 46% in gastrocnemius muscle and 54% in heart ventricle muscle microsomal suspensions derived from euthyroid rats. Thyroidectomy decreased specific [³H]ouabain binding by 37% and 56% in skeletal and heart muscle microsomes, respectively. Administration of triiodothyronine to thyroidectomized rats increased specific [³H]ouabain binding by 69% in gastrocnemius muscle and 425% in cardiac muscle membrane preparations. Scatchard analysis revealed that regulation of specific [³H]ouabain binding sites by triiodothyronine is mediated by alterations of dissociation constants and not by changes in the maximal number of binding sites. These observations are incompatible with the hypothesis that induction of (Na⁺ + K⁺)-ATPase of cardiac and skeletal muscle membrane is the molecular mechanism for the thermogenic action of thyroid hormones.

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ACKNOWLEDGMENTS The authors thank Ms. Lily S. Kung for measuring ATP hydrolytic activity in cardiac microsomal suspensions.