PYRIDOXINE-5'-BETA-D-GLUCOSIDE COMPETITIVELY INHIBITS UPTAKE OF VITAMIN-B6 INTO ISOLATED RAT-LIVER CELLS

Uptake of pyridoxine-5'-beta-D-glucoside by freshly isolated rat liver cells was studied at a concentration (0.5 mumol/L) approximating the physiological range of vitamin B-6 by using a membrane filtration method. Unlabeled pyridoxine glucoside was found to competitively inhibit the uptake of [4-H-3]pyridoxine but have no detectable effect on the uptake of D-[1-H-3]glucose by hepatocytes. The uptake of [H-3]pyridoxine glucoside by isolated rat liver cells was very similar to the uptake of [H-3]pyridoxine with K(t) = 13.8 mumol/L (6.3 mumol/L for pyridoxine) and V(max) = 82 pmol/(10(6) cells-min) [28 pmol/(10(6) cells-min for pyridoxine)]. The results of this study indicate that pyridoxine glucoside uses the same transport system as does pyridoxine. Upon entry to the cell, pyridoxine glucoside undergoes hydrolysis to release pyridoxine, which is the rate-limiting step in metabolism of this beta-glucoside.