Pyridoxine transport in brush border membrane vesicles of guinea pig jejunum.

Transport of [3H]pyridoxine was studied with membrane vesicles prepared from brush border of guinea pig jejunum, in which pyridoxal kinase was not detected. The imposition of an Na+ gradient across the membrane did not affect pyridoxine transport. The equilibrium level of pyridoxine uptake decreased with increasing osmolarity of the medium, which indicates that pyridoxine is transported into the membrane vesicles. The initial rate of pyridoxine uptake increased linearly with increasing pyridoxine concentration throughout the range of 0.18 microM to 7.4 microM both in the presence and absence of an Na+ gradient. 4'-Deoxypyridoxine and unlabeled pyridoxine, added in excessive amounts, did not inhibit pyridoxine transport into the membrane vesicles. These results substantiate the notion that pyridoxine passes through the brush border membrane by simple diffusion.