Rapid effects of 25-hydroxyvitamin D3 on calcium uptake in chick enterocytes

This study investigates the potential biological activity of 25(OH)D ₃ considered to be an inactive vitamin D₃ metabolite. In isolated enterocytes 25(OH)D₃ within 1 min decreased 45 Ca uptake to 54% of the controls. The enterocytes exhibited a biphasic dose response curve for 25(OH)D₃-stimulated calcium uptake and 24,25(OH)₂D₃ inhibited the stimulation. Increasing age decreased response to 25(OH)D₃ stimulated calcium uptake in isolated epithelial cells. BAY K8644, protein kinase A (PKA) activator forskolin, and phorbol ester treatment enhanced levels of 45Ca at T = 10 min (each, P < 0.05). 25(OH)D₃ increased PKA activity above corresponding controls at T = 1 min (89.8%, P < 0.05) and T = 3 min (78.4%). No evidence for the activation of PKC by 25(OH)D₃ was found.