ISSN:
1432-2013
Keywords:
Glutamine
;
Alanine
;
Arginine
;
Membrane carriers
;
Evoked currents
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
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.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00374679
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