Effects of thyroid hormone on Ca2+ efflux and Ca2+ transport capacity in rat skeletal muscle.
The present study was undertaken to investigate the effects of 3,5,3'-triiodothyronine (T3) treatment on passive Ca2+ efflux, Ca2(+)-dependent Mg2(+)-ATPase (Ca2(+)-ATPase) concentration and active Ca2+ transport in isolated rat skeletal muscle. In addition, the question was examined whether changes in Ca2+ efflux at rest and during electrical stimulation in the hyperthyroid state were accompanied by parallel changes in 3-O-methylglucose efflux. The resting Ca2+ efflux from rat soleus muscle was increased by 25% after 8 days of treatment with T3 (20 micrograms/100 g body weight). This was associated with a 78% increase in the basal efflux of 3-O-methylglucose. Electrical stimulation resulted in a rapid stimulation of Ca2+ efflux and 3-O-methylglucose efflux in the two groups of rats, and the levels obtained were significantly higher in the T3-treated group. The stimulating effect of the alkaloid veratridine on Ca2+ efflux was 60% larger in 8-day hyperthyroid rats. Within 24 h after the start of T3 treatment, a significant (21%) increase in Ca2(+)-ATPase concentration was detected. Significant increases in active Ca2+ uptake and passive Ca2+ efflux were not observed until after 2 and 3 days of T3 treatment, respectively. It is concluded that T3 stimulates the synthesis of Ca2+ ATPase and augments the intracellular Ca2+ pools (sarcoplasmic reticulum and mitochondria). The latter results in enhancement of the passive Ca2+ leak, which in turn, may lead to activation of substrate transport systems. The suggested increase in intracellular Ca2+ cycling after T3 treatment may, at least partly, explain the T3-induced stimulation of energy metabolism.
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Institute of Physiology, University of Aarhus, Denmark.
D019325:3-O-Methylglucose; D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase / Q000096:biosynthesis; D002118:Calcium / Q000378:metabolism / Q000493:pharmacokinetics* / Q000502:physiology; D000252:Calcium-Transporting ATPases / Q000032:analysis / Q000378:metabolism; D004558:Electric Stimulation; D005260:Female; D008757:Methylglucosides / Q000378:metabolism / Q000493:pharmacokinetics; D009132:Muscles / Q000032:analysis / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013997:Time Factors; D014284:Triiodothyronine / Q000494:pharmacology*; D014701:Veratridine / Q000494:pharmacology
D008757:Methylglucosides; D014284:Triiodothyronine; D019325:3-O-Methylglucose; D014701:Veratridine; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases; D002118:Calcium