[Mechanism of intestinal vitamin-D-dependent Ca absorption. Correlation between active Ca transport and release of inorganic phosphate on the basal side of intestinal epithelia].

Incubation of isolated sections of rat small intestine in air-saturated medium, deprived of inorganic phosphate (Pi) was accompanied by liberation of endogenous Pi from both sides of the intestinal wall as well as by development of the anion concentration gradient, which was directed from apical to basal side of the wall. After addition into medium of 0.25 mM CaCl2 triggering the Ca2+ absorption in the isolated intestinal section by an active transport mechanism, distinct output of Pi was observed at the basal side of the intestinal epithelium against the concentration gradient of the anion. Under anaerobic conditions block of Ca2+ active transport by means of inhibitors of energy supply (1 . 10(-5) M DNP, 4 . 10(-6) M p-chloromercuribenzoate) inhibited simultaneously the Pi output; the same phenomenon was observed in aged rats and in rats maintained on D-avitaminous diet, thus demonstrating the intimate relation of the processes studied. The data obtained are consistent with the idea on existence of a phosphorylated carrier of Ca2+, dephosphorylation of which on basal-lateral membrane of enterocyte is accompanied by simultaneous liberation of Ca2+ and Pi from the mucosal cells providing the energy-dependent transition of the ions against the concentration gradient.