ISSN:
0021-9541
Keywords:
Life and Medical Sciences
;
Cell & Developmental Biology
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Biology
,
Medicine
Notes:
Recent investigations have indicated that cellular rheogenic properties may interfere with the correct estimation of Na+ and amino transport stoichiometry. We have reevaluated the stoichiometry of Na+ and α-aminoisobutyric acid (α-AIB) cotransport in Ehrlich ascites tumor cells depleted of Na+ and ATP by incubation in Na+ -free HEPES-buffered medium (pH 7.2) containing 160 mM K+ and 2.5 μM valinomycin. Transfer of the cells to a medium with 10 mM 22Na+, 10 mM 3H-AIB, and 150 mM K+ resulted in an enhancement of Na+ flux above basal levels, which represents 0.6 of the AIB uptake. Under these conditions the membrane potential, -7.0 ± 0.1 mV (SEM), does not change with the addition of AIB, -7.3 ± 0.6 mV (SEM). HgCl2 (10 m̈M) added to the medium inhibited AIB flux and AIB-stimulated Na+ flux by 45-50% but did not change the coupling ratio. HgCl2 (10 m̈M) does not inhibit the basal Na+ flux nor does it affect cellular Na+ or K+ content. In physiological medium cotransport is electrogenic. The membrane potential of Ehrlich cells in physiological medium is -22.3 ± 0.8 mV (SEM) and depolarizes to -16.7 ± 0.7 mV (SEM) upon addition of AIB. Under these conditions the coupling ratio was highly variable but the ratio of codepression is 0.90 ± 0.02 (SEM) in the presence of HgCl2 (10 m̈M). These results are consistent with a model (Smith and Robinson, 1981) in which the stoichiometry is one cosubstrate molecule per molecule of α-AIB. We suggest that H+ provides the alternative cosubstrate in this low Na+ environment and that in high Na+ medium the Na+ :AIB stoichiometry approaches 1:1.
Additional Material:
6 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/jcp.1041150205
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