Abstract
1,25-Dihydroxyvitamin D 3 has been shown to induce rapid changes in calcium fluxes in skeletal muscle and other target tissues independently of gene activation. The possibility that the hormone would produce similar effects in heart where 1,25-dihydroxyvitamin D 3 receptors and activities have been shown, was studied. A significant increase of 45Ca uptake by left ventricular slices from vitamin D-deficient chicks was observed upon incubation for 1–10 min with physiological doses of 1, 25-dihydroxyvitamin D 3. This stimulation was dose-dependent and specific for the hormone when compared with vitamin D 3, 25-hydroxyvitamin D 3 and 24,25-dihydroxyvitamin D 3 and could not be associated to changes in lipid synthesis as assessed by measurements of [ 3H]glycerol incorporation into cardiac tissue lipids. The Ca channel blockers nifedipine (30 μM) and verapamil (10 /gmM) abolished the increase in Ca uptake produced by 1,25-dihydroxyvitamin D 3. The rapid effects of the hormone on heart Ca influx were accompanied by a stimulation of the phosphorylation of two microsomal proteins of 43 kDa and 55 kDa. These results further support a direct action of 1,25-dihydroxyvitamin D 3 in the regulation of cardiac muscle Ca metabolism which may involve activation of Ca channels.
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