Regulation of 25 hydroxyvitamin D3 1-hydroxylase in serum-free monolayer culture of mouse kidney.

Primary monolayer cultures of cells from normal mouse kidney were initiated and maintained in serum-free medium supplemented with insulin, transferrin and prostaglandin E1. Renal epithelial cells grow to confluence without detectable growth of fibroblasts. These cells contain an active 25(OH)D3 1-hydroxylase with half-maximal formation of 1,25(OH)2D3 achieved at a substrate concentration of 13.3 nM. Activity of this enzyme is increased by low calcium medium or parathyroid hormone and decreased by high calcium medium, high phosphate medium or 1,25(OH)2D3.