Triiodothyronine augments the number of membrane-bound (Na+-K+)-adenosine triphosphatase units, but does not affect the sedimentation properties of plasma membrane components.

We have previously demonstrated that T3 enhanced the de novo synthesis of renal cortical (Na+-K+)-dependent ATPase (NaK-ATPase) in the rat. A purified membrane fraction obtained from successive centrifugation of renal cortical crude homogenate was used in the above studies. To rule out a possible effect of T3 on plasma membrane properties, such as the sedimentation characteristic of NaK-ATPase, we have presently observed T3-dependent increases in the activity and number of NaK-ATPase units in a crude homogenate of rat renal cortex. The following results were obtained which substantiate a specific effect of T3 on the membrane-bound NaK-ATPase system. 1) Compared to the hypothyroid state, 43% and 44% increases in the activity and number of NaK-ATPase units, respectively, were observed in crude renal cortical homogenate of T3-treated hypothyroid rats. 2) In comparison with the crude homogenate prepared from hypothyroid rats, 4.8- and 113-fold increases in the specific activity of NaK-ATPase were obtained in the L and J fractions, respectively. Increases of similar relative magnitude in the L and J fractions were also shown in T3-treated hypothyroid and euthyroid rats. 3) No difference in the recovery of the number of NaK-ATPase units was observed from successive steps of the purification under different thyroid states. 4) Treatment of renal cortices from hypothyroid, T3-treated hypothyroid, and euthyroid rats with deoxycholate increased to the same extent NaK-ATPase activity and phosphorylated intermediate formation.