title: Thyroid hormone-induced upregulation of Na+ channels and Na(+)-K+ pumps: implications for contractility.
abstract: We have previously observed in rat soleus muscle that endurance is a function of the ratio between the concentration of Na+ channels and Na(+)-K+ pumps [Harrison, A. P., O. B. Nielsen, and T. Clausen. Am. J. Physiol. 272 (Regulatory Integrative Comp. Physiol. 41): R1402-R1408, 1997]. In this study we explore this relationship further by comparing the changes in Na+ channel and Na(+)-K+ pump concentrations induced by injections of 3,5,3'-triiodothyronine (T3) with endurance. T3 induced upregulation of the concentration of Na+ channels and Na(+)-K+ pumps, which was associated with a progressive loss of contractile endurance. The increase in Na+ channels preceded that of the Na(+)-K+ pumps and amounted to 49 and 52% (both P < 0.01) after 48 and 72 h of T3 treatment, respectively. Concomitantly, during 90-Hz stimulation, the initial rate of force decline increased by 42 and 45% after 48 and 72 h of T3 treatment, respectively (both P < 0.001). These observations are important for an understanding of the fatigue associated with hyperthyroidism and add further support to the hypothesis that muscle endurance depends on the leak-to-pump ratio for Na+.
authors.affiliation: Department of Physiology, University of Aarhus, Denmark.
authors.forename: A P
authors.initials: AP
authors.lastname: Harrison
authors.forename: T
authors.initials: T
authors.lastname: Clausen
mesh_terms: D000367:Age Factors; D000818:Animals; D006980:Hyperthyroidism / Q000503:physiopathology; D009119:Muscle Contraction / Q000187:drug effects*; D010042:Ouabain / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D012530:Saxitoxin / Q000378:metabolism; D015222:Sodium Channels / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D013997:Time Factors; D014284:Triiodothyronine / Q000494:pharmacology*; D015854:Up-Regulation / Q000187:drug effects
chemical_list: D015222:Sodium Channels; D014284:Triiodothyronine; D012530:Saxitoxin; D010042:Ouabain; D000254:Sodium-Potassium-Exchanging ATPase