AJP - Endocrinology and Metabolism, Vol 247, Issue 4 421-E430, Copyright © 1984 by American Physiological Society
Effect of thyroid status on K+-stimulated metabolism and 45Ca exchange in rat skeletal muscle
C. Van Hardeveld and T. Clausen
In the perfused hindlimbs of hypo-, eu-, and hyperthyroid rats, high K+o
(20 mM) markedly stimulated glucose uptake, lactate production, and
O2-consumption to levels increasing with the thyroid status. At Ca2o+ less
than 50 microM, all the responses became transient. In the hypothyroid
preparations, caffeine (5 mM) produced no stimulation, but in those
obtained from eu- and hyperthyroid rats, it increased all the metabolic
parameters as well as K+ release in proportion to thyroid status. In
isolated soleus and extensor digitorum longus muscles, both high K+o and
caffeine stimulated 45Ca-efflux, with the response increasing in proportion
to thyroid status. This stimulation was reduced by 70-100% with dantrolene
(10(-5) M), which in earlier studies was shown to suppress the metabolic
effects of high K+o and caffeine. High K+o also increased 45Ca-influx but
produced no change in muscle calcium contents. The results support the idea
that thyroid hormones control substrates availability and energy
consumption in skeletal muscle by increasing the amount of sarcoplasmic
reticulum and thereby the rate of Ca2+ mobilization into the cytosol.
