AJP - Gastrointestinal and Liver Physiology, Vol 262, Issue 1 150-G158, Copyright © 1992 by American Physiological Society

ARTICLES

Transport of 5-methyltetrahydrofolate in basolateral membrane vesicles of rat liver

D. W. Horne, K. A. Reed and H. M. Said
Biochemistry Research Laboratory (151), Department of Veterans Affairs Medical Center, Nashville 37212-2637.

We examined 5-methyltetrahydrofolate transport across the basolateral membrane (BLM) of rat liver using isolated membrane vesicles. Uptake of 5-methyltetrahydrofolate by BLM vesicles (BLMV) was found by osmolarity and initial uptake studies to be mostly the result of transport of the substrate into an active, intravesicular space with some binding (approximately 25%) to membrane surfaces. Uptake was similar in the presence of an inwardly directed Na+ or K+ gradient, indicating that transport is not dependent on Na+. Uptake of 5-methyltetrahydrofolate was linear for the first 30 s and was more rapid when an initial pH gradient was imposed across the vesicular membrane [extravesicular pH (pHo) = 5.0, intravesicular pH (pHi) = 7.5]. Under pH gradient conditions, uptake at 3-5 min was about twofold higher than at equilibrium (60 min). The initial rate of uptake at pHo = pHi = 5.0 was more rapid than at pHo = pHi = 7.5, but in neither case was uptake above equilibrium observed. Uptake under pH gradient conditions and at pH 5.0 (no pH gradient) was saturable (apparent Michaelis constants of 0.58 and 0.36 microM, respectively; maximum uptake rates of 1.25 and 0.79 pmol.10 s-1.mg protein-1, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

This article has been cited by other articles:

				S. M. Nabokina, T. Y. Ma, and H. M. Said Mechanism and regulation of folate uptake by human pancreatic epithelial MIA PaCa-2 cells Am J Physiol Cell Physiol, July 1, 2004; 287(1): C142 - C148. [Abstract] [Full Text] [PDF]

				Y.-H. Han, Y. Kato, Y. Watanabe, K. Terao, Y. Asoh, and Y. Sugiyama Carrier-Mediated Hepatobiliary Transport of a Novel Antifolate, N-[4-[(2,4-Diamminopteridine-6-yl)methyl]-3,4-dihydro-2H-1,4-benzothiazin-7-yl]carbonyl-L-Homoglutamic Acid, in Rats Drug Metab. Dispos., April 1, 2001; 29(4): 394 - 400. [Abstract] [Full Text]

				Y.-H. Han, Y. Kato, H. Kusuhara, H. Suzuki, M. Shimoda, E. Kokue, and Y. Sugiyama Kinetic profile of overall elimination of 5-methyltetrahydropteroylglutamate in rats Am J Physiol Endocrinol Metab, March 1, 1999; 276(3): E580 - E587. [Abstract] [Full Text] [PDF]

				J. Villanueva, E.-H. Ling, C. J. Chandler, and C. H. Halsted Membrane and tissue distribution of folate binding protein in pig Am J Physiol Regulatory Integrative Comp Physiol, November 1, 1998; 275(5): R1503 - R1510. [Abstract] [Full Text] [PDF]

				C. D. Chancy, R. Kekuda, W. Huang, P. D. Prasad, J.-M. Kuhnel, F. M. Sirotnak, P. Roon, V. Ganapathy, and S. B. Smith Expression and Differential Polarization of the Reduced-folate Transporter-1 and the Folate Receptor alpha in Mammalian Retinal Pigment Epithelium J. Biol. Chem., June 30, 2000; 275(27): 20676 - 20684. [Abstract] [Full Text] [PDF]