Molecular Pharmacology, Vol 14, 1204-1211, Copyright © 1978 by the American Society for Pharmacology and Experimental Therapeutics

Denervation of Cat Fast- and Slow-Skeletal Muscles: Effect on Ouabain Binding

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

The specific binding of [³H]ouabain in microsomal suspensions obtained from slow-contracting soleus and fast-contracting tibialis anterior is approximately 200% and 10%, respectively, of that seen in the microsomes of the mixed type gastrocnemius muscle. Chemical sympathectomy decreased specific binding of [³H]ouabain by 90% in the soleus and 33% in the tibialis anterior muscle microsomes. Scatchard analysis revealed that the fall in specific binding of [³H]ouabain in muscles obtained from sympathectomized cats was due to a marked decrease in the density of ouabain binding sites. The equilibrium dissociation constants decreased in all three types of muscles after administration of 6-hydroxydopamine. Ablation of the motor nerve, which involves surgical sympathectomy, increased specific binding of [³H]ouabain by 20 to 40% in soleus and gastrocnemius muscle microsomal preparations. Kinetic analysis by reciprocal plots suggested that the enhancement of ouabain binding after denervation is due to changes in the total number of binding sites, and not the affinity constant. Since ouabain selectively binds to (Na⁺ + K⁺)-ATPase, these observations provide support for the hypothesis that the motor nerve may be involved in the regulation of the number of (Na⁺ + K⁺)-ATPase molecules in skeletal muscles. An increase in ouabain binding and (Na⁺ + K⁺)-ATPase activity following ablation of the motor nerve would suggest that the fall in resting membrane potential of denervated skeletal muscle may not be due to decrease in (Na⁺ + K⁺)-ATPase activity.