Effects of vitamin D metabolites on calcium fluxes in intact chicken skeletal muscle and myoblasts cultured in vitro.

25-hydroxycholecalciferol (25OHD) and 1,25-dihydroxycholecalciferol (1,25(OH)D) at physiological concentrations exerted direct effects on Ca fluxes in cultured vitamin D-deficient chick soleus muscle and myoblasts. Isotopic desaturation curves of soleus muscle prelabeled withCa indicated that the action of 25OHD is localized in a slow-exchangeable Ca pool where it stimulates net Ca uptake. On the other hand, the predominant effects of 1,25(OH)D consist in an increase of the rate constant of Ca efflux of this pool and in an increase of net Ca uptake in a fast-exchangeable pool. 24,25-dihydroxycholecalciferal proved to be inactive on both Ca uptake and efflux. In addition, 1,25(OH)D significantly increasedCa labeling of cultured chick myoblasts. These effects were accompanied by changes in the growth and differentiation of the cultures. The results suggest a direct involvement in vivo of 25OHD and 1,25(OH)D on muscle cellular calcium. [ABSTRACT FROM AUTHOR]