Effects of vitamin D3 metabolites on calcium fluxes in intact chicken skeletal muscle and myoblasts culturedin vitro

Abstract

25-hydroxycholecalciferol (25OHD₃) and 1,25-dihydroxycholecalciferol (1,25(OH)₂D₃) 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 with⁴⁵Ca indicated that the action of 25OHD₃ 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)₂D₃ 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)₂D₃ significantly increased⁴⁵Ca labeling of cultured chick myoblasts. These effects were accompanied by changes in the growth and differentiation of the cultures. The results suggest a direct involvementin vivo of 25OHD₃ and 1,25(OH)₂D₃ on muscle cellular calcium.