The kinetics of vitamin D₃ in the osteoblastic cell.

Experimental evidence is presented on the translocation of vitamin D metabolite, 1,25-(OH)₂D₃, from the membrane to the nucleus in osteoblast progenitor cells. A mathematical model permitting traversal of the cytoplasm at either a fixed velocity or by diffusion is formulated in order to determine whether transport along the cytoskeletal tracks is more consistent with the observed spatial-temporal distribution than diffusion, and it is so found. The model includes reactions in the nucleus involving D₃ to form other compounds, such as protegerin, and thus also makes predictions of the concentrations of these compounds in various regions of the cell.