Abstract
Using electrophysiological and radiotracer studies in parallel, we have investigated the characteristics of the endogenous Na+-dependent amino acid transporter (system B0,+) in Xenopus oocytes with regard to ion dependence, voltage dependence and transport stoichiometry. In voltage-clamped oocytes (−60 mV) superfusion with saturating concentrations of amino acids (1 mM) in 100 mM NaCl resulted in reversible, inward currents (mean±SEM): alanine, 1.83±0.09 nA (n=21); arginine, 2.54±0.18 nA (n=17); glutamine, 1.73±0.10 nA (n=19). Only arginine evoked a current in choline medium (0.50±0.13 nA, n=10), whereas Cl− replacement had no effect on evoked currents. The glutamine-evoked current was saturable (I max=1.73 nA, glutamine K m=0.12 mM) and linearly dependent upon voltage between −90 and −30 mV. Using direct and indirect (activation) methods, we found that transport can proceed with Na+/amino acid coupling stoichiometry of either 1∶1 or 2∶1, but coupling was the same for each amino acid tested (alanine, arginine and glutamine) within a batch of oocytes (i.e. from a single toad). Despite the net single positive charge on arginine, the magnitude of the net transmembrane charge movement during Na+-coupled arginine transport was identical to that for the zwitterionic neutral amino acids glutamine and alanine; this may be explained by a concomitant stimulation of K+ efflux during arginine transport with a putative coupling of 1 K+∶1 arginine.
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Barbour B, Brew H, Attwell D (1991) Electrogenic uptake of glutamate and aspartate into glial cells isolated from the salamander (Ambystoma) retina. J Physiol (Lond) 436:169–193
Campa MJ, Kilberg MS (1989) Characterization of neutral and cationic amino acid transport in Xenopus oocytes. J Cell Physiol 141:645–652
Christensen HN (1990) Role of amino acid transport and countertransport in nutrition and metabolism. Physiol Rev 70:43–77
Christensen HN, Liang M, Archer EG (1967) A distinct Na+- requiring transport system for alanine, serine, cysteine, and similar amino acids. J Biol Chem 242:5237–5246
Jung D, Schwarz W, Passow H (1984) Sodium-alanine co-transport in oocytes of Xenopus laevis: correlation of alanine and sodium fluxes with potential and current changes. J Membr Biol 78:29–34
Kaur S, Mackenzie B, Taylor PM (1992) Modulation of amino acid transport in Xenopus oocytes in relation to environmental amino acid availability (abstract). J Physiol (Lond) 446:13P
Kavanaugh MP, Kabat D (1993) Voltage-dependence of basic amino acid transport mediated by murine system y+ cloned and expressed in Xenopus oocytes (abstract). J Physiol (Lond) 459:179P
Kilberg MS, Handlogten ME, Christensen HN (1981) Characteristics of system ASC for transport of neutral amino acids in isolated rat hepatocytes. J Biol Chem 256:3304–3312
Loo DDF, Supplisson S, Turk E, Wright EM (1992) Charge movements associated with the Na+/glucose cotransporter cloned from human intestine (abstract). FASEB J 6:A1768
Neher E (1971) Two fast transient current components during voltage clamp on snail neurons. J Gen Physiol 58:36–53
Reshkin SJ, Grover ML, Howerton RD, Grau EG, Ahearn GA (1989) Dietary hormonal modification of growth, intestinal ATPase, and glucose transport in tilapia. Am J Physiol 256:E610-E618
Schnetkamp PPM, Szerencsei RT, Basu DK (1991) Unidirectional Na+, Ca2+, and K+ fluxes through the bovine outer segment Na-Ca-K exchanger. J Biol Chem 266:198–206
Sigel E (1990) Use of Xenopus oocytes for the functional expression of plasma membrane proteins. J Membr Biol 117:201–221
Stein, WD (1986) Transport and diffusion across cell membranes. Academic Press, San Diego
Stevens BR (1992) Amino acid transport in intestine. In: Kilberg MS, Häussinger D (eds) Mammalian amino acid transport: mechanisms and control. Plenum Press, New York, pp 149–163
Su TZ, Oxender DL (1991) Characterization and expression of l-leucine transport in Xenopus oocytes (abstract). FASEB J 5:A1188
Taglialatela M, Toro L, Stefani E (1992) Novel voltage clamp to record small, fast currents from ion channels expressed in Xenopus oocytes. Biophys J 61:78–82
Taylor PM, Hundal HS, Rennie MJ (1989) Transport of glutamine in Xenopus laevis oocytes: relationship with transport of other amino acids. J Membr Biol 112:149–157
Van Winkle LJ, Christensen HN, Campione AL (1985) Na+-dependent transport of basic, zwitterionic, and bicyclic amino acids by a broad-scope system in mouse blastocysts. J Biol Chem 260:12118–12123
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Mackenzie, B., Harper, A.A., Taylor, P.M. et al. Na+/amino acid coupling stoichiometry of rheogenic system B0,+ transport in Xenopus oocytes is variable. Pflugers Arch. 426, 121–128 (1994). https://doi.org/10.1007/BF00374679
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DOI: https://doi.org/10.1007/BF00374679