[Calcium binding by rat small intestine epithelium microvilli at different contents of vitamin D]

Vitamin D does not essentially affect the association constants and the number of sites of Ca2+ binding by small intestine epithelium microvilli. Ca2+ binding to the lipids isolated from the microvilli is similar to Ca2+ binding by intact microvilli in some parameters, e. g. existence of two types of binding sites, values of association constants and number of sites. This is in agreement with the assumption on the possible role of phospholipids in the mechanism of Ca2+ binding by the microvilli. The deficiency of vitamin D does not affect Ca2+ binding by microvilli lipids. The data obtained suggest that the insufficiency of Ca2+ transport in the intestine under vitamin D deficiency probably affects Ca2+ transfer processes other than Ca2+ binding to the microvilli membrane.