1,25-Dihydroxyvitamin D3 stimulates 45Ca2+ uptake by cultured adult rat ventricular cardiac muscle cells.

This study tested the hypothesis that 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) and its previously described cardiac receptors play roles in regulating intracellular calcium homeostasis in cardiac muscle cells. This question was addressed by assessing whether 1,25-(OH)2D3 influences 45Ca2+ uptake by homogeneous cultures of adult rat ventricular cardiac muscle cells. Twenty-four h prior to the measurement of 45Ca2+ uptake, the cells were transferred to serum-free medium ([Ca2+], 1.0 mM) containing 1.0 nM 1,25(OH)2D3 or vehicle. The cells were then incubated with 45Ca2+ for periods up to 60 min at room temperature, followed by removal of excess external 45Ca2+ by washing repeatedly with La3+. Pretreating the cells with 1,25-(OH)2D3 caused 3-fold stimulation (p less than 0.005) of 45Ca2+ uptake. Stimulation of 45Ca2+ uptake required a prolonged (8-12 h) exposure to 1,25-(OH)2D3, suggesting a receptor-mediated phenomenon. Concentrations of 0.01-10 nM 1,25-(OH)2D3 yielded a dose-response curve which peaked at 1.0 nM and decreased at higher concentrations. Steroid specificity was established by the failure of 1.0 nM levels of 25-hydroxyvitamin D3, estradiol-17 beta, and progesterone to change 45Ca2+ uptake. Sucrose gradient analysis confirmed the presence of a specific 3-4 S 3H-1,25-(OH)2D3 binding component both in freshly isolated and in cultured ventricular cardiac muscle cells. The stimulatory effect of 1,25-(OH)2D3 on 45Ca2+ uptake was abolished by the concomitant incubation of the cells with cycloheximide or actinomycin D, demonstrating a requirement for protein and nucleic acid synthesis. In conclusion, these data demonstrate that 1,25-(OH)2D3 stimulates 45Ca2+ uptake in adult ventricular cardiac muscle cells by a mechanism resembling a receptor-mediated phenomenon.