The effect of tri-iodothyronine on the membrane potential and intracellular sodium and potassium activities of rat soleus and extensor digitorum longus muscles.

Tri-iodothyronine (T 3 ) induces a considerable increase in the number of Na/K pump units in rat skeletal muscles, but this effect is more pronounced in red muscles, such as soleus, than in white muscles such as extensor digitorum longus (EDL). In the present study, the effect of T 3 on the membrane potential (E m ) and the intracellular activities of K + and Na + +(aK i and aNa i ) in the two muscle types has been studied using microelectrodes