Thyroid hormones up-regulate Ca-channels in cultured skeletal muscle of the rat

The effects of thyroid hormones (TH) were examined on the expression of slow Ca²⁺-channels in cultures of rat skeletal muscle. Myotubes were treated with TH at age 5-7 days in vitro, and measurements of specific binding of the dihydropyridine Ca-channel antagonist [³H]PN200-110 were made beginning 12 h later. TH caused a dose-related increase in PN200-110 binding sites with a lower affinity for the ligand than in control cells. The effect was blocked by simultaneous treatment with cycloheximide or actinomycin-D. The results indicate that TH increase gene expression of slow Ca²⁺-channels of skeletal muscle.