Pyridoxine uptake by rat renal proximal tubular cells.
Uptake of [3H]pyridoxine by freshly isolated rat renal proximal tubular cells was temperature dependent and exhibited saturation kinetics, with estimated Kt and Vmax of 1.3 microM and 14 pmol/(10(6) cells.0.5 min), respectively. Pyridoxamine, 4'-deoxypyridoxine and 5'-deoxypyridoxal were as effective as unlabeled pyridoxine in inhibiting tracer uptake, whereas pyridoxamine-5'-phosphate, pyridoxal and 4'-pyridoxic acid had no effect, and other vitameric forms and structural analogs caused intermediate inhibition of cellular vitamin uptake. After 30 min, 88% of accumulated radioactive vitamin B-6 in cell extracts had been metabolized to phosphorylated forms and pyridoxal, which supports metabolic trapping as a mechanism responsible for the cellular accumulation observed. Initial uptake was significantly decreased in the presence of ethionine and ouabain; however, carbonylcyanide-p-trifluoromethoxyphenylhydrazone had no effect. Partial to complete substitution of NH4Cl and LiCl for NaCl had no effect, while partial substitution with RbCl caused significant dose-related inhibition of initial pyridoxine uptake. Amiloride also significantly decreased initial uptake. These data are consistent with a facilitated uptake process for pyridoxine that has substrate specificity and may be modulated by sodium-hydrogen exchange and/or pH gradient effects. Cellular uptake is followed by intracellular metabolic trapping catalyzed by pyridoxal kinase.
Bowman
B B
BB
Department of Biochemistry, Emory University School of Medicine, Atlanta, GA 30322.
McCormick
D B
DB
D000818:Animals; D001667:Binding, Competitive; D002469:Cell Separation; D002851:Chromatography, High Pressure Liquid; D007425:Intracellular Membranes / Q000378:metabolism; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000378:metabolism*; D008297:Male; D009994:Osmolar Concentration; D011736:Pyridoxine / Q000493:pharmacokinetics*; D051381:Rats; D011919:Rats, Inbred Strains
D011736:Pyridoxine