Effect of pyridoxine deficiency on intestinal absorption of calcium and oxalate: chemical composition of brush border membranes in rats.

[U-14C]oxalic acid and 45Ca uptake was measured in control and vitamin B6-deficient rats. Calcium and oxalate uptake rates were significantly increased from the intestine of vitamin B6-deficient rats as compared to pair-fed controls. Oxalate uptake in pair-fed control rats follows a passive diffusion. In pyridoxine-deficient rats, the oxalate uptake increases nonlinearly as the oxalate concentration in the incubation medium increased, indicating a two-component system--a saturable sodium-independent uptake and a linear nonsaturable passive-diffusion component. The brush border membrane composition reveals that membrane sialic acid, cholesterol, and protein contents were markedly reduced. These aberrations in the chemical composition of brush border membrane may be responsible for the enhanced oxalic acid uptake in vitamin B6-deficient rats.