NA+/AMINO ACID COUPLING STOICHIOMETRY OF RHEOGENIC SYSTEM B-0,B-+ TRANSPORT IN XENOPUS-OOCYTES IS VARIABLE

被引:16
作者
MACKENZIE, B [1 ]
HARPER, AA [1 ]
TAYLOR, PM [1 ]
RENNIE, MJ [1 ]
机构
[1] UNIV DUNDEE,DEPT ANAT & PHYSIOL,DUNDEE DD1 4HN,SCOTLAND
来源
PFLUGERS ARCHIV-EUROPEAN JOURNAL OF PHYSIOLOGY | 1994年 / 426卷 / 1-2期
基金
英国惠康基金;
关键词
GLUTAMINE; ALANINE; ARGININE; MEMBRANE CARRIERS; EVOKED CURRENTS;
D O I
10.1007/BF00374679
中图分类号
Q4 [生理学];
学科分类号
071003 ;
摘要
Using electrophysiological and radiotracer studies in parallel, we have investigated the characteristics of the endogenous Na+-dependent amino acid transporter (system B-0,B-+) in Xenopus oocytes with regard to ion dependence, voltage dependence and transport stoichiometry. In voltage-clamped oocytes (-60mV) 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.
引用
收藏
页码:121 / 128
页数:8
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