Dependence of renal (Na+ + k+)-adenosine triphosphatase activity on thyroid status.
In thyroidectomized rats, a single injection of L-2,,5,2'-triiodothyronine (T3) (50mug/100 g body weight) elicited at 45% increase in (Na+ + k+)-dependent adenosine triphosphatase (NaK-ATPase) activity of the membrane-rich fraction of renal cortex at the optimal time of response, 48 h after injection. Three successive doses of T3 (50 mug/100 g body weight), given on alternate days, increased NaK-ATPase by 67% in the renal cortex but had no significant effect on the outer medulla or the papilla. Moreover, T3 had no effect on Mg2+-dependent adenosine trisphatase (MgATPase) in cortex, cedulla, or papilla. Three doses of T3 (50 mug/100 g body weight) given on alternate days to thyroidectomized rats elecited a 134, 79, and 46% increase in Vmax for ATP, Na4, and K+, respectively. There were no changes in the Km for ATP or the K1/2 values for Na+ and K+. Two methods were used to estimate the effect of T3 on the number of NaK-ATPase units (assumed to represent the number of Na+ pump sites); rat renal plasma membrane fractions were incubated with [gamma-32P]ATP, Mg2+, and Na+; the 32P-labeled membrane protein yeild was quantitatively dependent on Na+ and was hydrolyzed on addition of K+. There was a linear correlation between the specific activity of NaK-ATPase (Vmax) and the amount of phosphorylated intermediate formed, in renal cortical membrane fractions from thyroidectomized rats given T3 or the diluent. There was also a linear correlation between the specific activity of NaK-ATPase (Vmax) and the amount of [3H]ouabain specifically bound (Na+-, Mg2+-, APT-dependent) to the NaK-ATPase preparation. Injection of T3 resulted in a 70% increase in NaK-ATPase activity, a 79% increase in formation of the phosphorylated intermediate, and a 65% increase in the [H]ouabain specifically bound to the NaK-ATPase system. The T3-dependent increases in Vmax for ATP, Na+, and K+ and the proportionate increases in the phosphorylated intermediate and in the amount of [3H]ouabain bound indicate that T3 increases the number of NaK-ATPase units and that this increase accounts for the increase in NaK-ATPase activity.
D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000818:Animals; D004789:Enzyme Activation; D005260:Female; D007668:Kidney / Q000201:enzymology*; D007672:Kidney Cortex / Q000187:drug effects / Q000201:enzymology; D007679:Kidney Medulla / Q000201:enzymology; D007700:Kinetics; D010042:Ouabain / Q000378:metabolism; D011188:Potassium / Q000494:pharmacology; D011485:Protein Binding; D051381:Rats; D012964:Sodium / Q000494:pharmacology; D013961:Thyroid Gland / Q000502:physiology*; D013965:Thyroidectomy; D014284:Triiodothyronine / Q000494:pharmacology
D014284:Triiodothyronine; D010042:Ouabain; D012964:Sodium; D000251:Adenosine Triphosphatases; D011188:Potassium