AJP - Cell Physiology, Vol 232, Issue 5 196-C201, Copyright © 1977 by American Physiological Society

ARTICLES

Thyroid hormone control of Na+-K+-ATPase and K+-dependent phosphatase in rat heart

K. D. Philipson and I. S. Edelman

To assess the possible role of the Na+ pump in mediating physiological responses to thyroid hormone in the rat myocardium, we examined the effects of L-3,5,3'-triiodothyronine (T3) on the activities of the closely associated enzymes, Na+-K+-dependent adenosine triphosphatase (Na-K-ATPase) and K+-dependent p-nitrophenyl phosphatase (K-dep-pNPPase). In hypothyroid rats, administration of T3 (50 microng/100 g body wt) resulted in significant increases (greater than 50%) in Na-K-ATPase and K-dep-pNPPase activities in both crude homogenates and microsomal fractions of the rat ventricle. Significant effects on Na-K-ATPase activity were also attained with low doses (1 microng/100 g body wt) of T3. A method was developed for assaying K-dep-pNPPase activity in cardiac slices. With this technique, enhancement in K-dep-pNPPase activity of 89.2% was found in ventricle slices after treatment of hypothyroid rats with T3 (50 microng/100 g body wt), implying that augmentation of the capacity of the Na+ pump is achieved in vivo. The potent analogue, L-3,5-diiodo-3' isopropyl thyronine (isopropyl T2) had the same effects on cardiac growth and Na-K-ATPase as T3, in hypothyroid rats. In contrast, the relatively inactive isomer, L-3,3',5'-triiodothyronine (reverse T3) had no significant effect on the heart weight-to-body weight ratio or on ventricular Na-K-ATPase activity.

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				J. D. Walker, F. A. Crawford Jr., R. Mukherjee, and F. G. Spinale THE DIRECT EFFECTS OF 3,5,3'-TRIIODO-L-THYRONINE (T3) ON MYOCYTE CONTRACTILE PROCESSES: Insights into mechanisms of action J. Thorac. Cardiovasc. Surg., November 1, 1995; 110(5): 1369 - 1380. [Abstract] [Full Text]