1,25-Dihydroxyvitamin D3 receptors identified in the rat heart

Specific receptors for 1,25-dihydroxyvitamin D3, the active hormonal form of vitamin D3, were demonstrated in low salt chromatin preparations from normal rat hearts. Sucrose gradient analysis of KCl-extracted chromatin yielded a significant (P less than 0.005) peak of specific [3H]1,25-dihydroxyvitamin D3 binding in the 3.6S region. The peak of [3H]1,25-dihydroxyvitamin D3 binding was abolished by excess 1,25-dihydroxyvitamin D3, but not by 50 nM 25-hydroxyvitamin D3 nor by 1.0 microM levels of estradiol-17B, cortisol, or promegestone, demonstrating steroid specificity characteristic for such receptors. Upon Scatchard analysis this putative cardiac 1,25-dihydroxyvitamin D3 receptor yielded a single binding component with high affinity (KD = 0.36 nM) and low capacity (Nmax = 33 fmol/g tissue). Coupled with evidence for the presence of calcium binding proteins in this tissue, these observations suggest functional roles for 1,25-dihydroxyvitamin D3 and its receptors in cardiac muscle, possibly in regulating intracellular effects of calcium.