Thyroid hormone (T3) induces an increase in the number of Na t-K § pumps in rat extensor digitorum longus (e.d.1.) muscles It). In this study, the effect of T3 on the membrane potential, Em and the intracellular Na + and K § activities,...
moreThyroid hormone (T3) induces an increase in the number of Na t-K § pumps in rat extensor digitorum longus (e.d.1.) muscles It). In this study, the effect of T3 on the membrane potential, Em and the intracellular Na + and K § activities, aN i and akl of these muscles have been determined, using microelectrodes. Rats were rendered hyperthyroid by 6-7 s.c. injections of T 3 (501.tg/100g). In the sera of three control and three hyperthyroid rats, T 3 levels were 1.1mM :1= 0.16 and 8.4aM • 0.46 respectively. In four hyperthyroid muscles, Em depolarized, decreasing significantly from 79mV _+ 3 (n = 39) in control fibres to 77mV s: 4 (n= 53) (P < 0.01). a re'was llmM+3 (n= 13) and ak~ was 109raM _+ 24, (n = 24) in the hyperthyroid muscles. These values were 9mM-. 3, (n = 10) and 120 + 27, (n = 24) respectively in control muscles. Neither of the activity changes reached significance. These results may reflect changes in the passive fluxes of Na" and K ~, which have been shown to occur ~ in association with the increase in pump number.
