Document Detail

Energetics of Na+-dependent amino acid co-transport in Ehrlich ascites tumor cells.
MedLine Citation:
PMID:  3801480     Owner:  NLM     Status:  MEDLINE    
The energy available from the Na+ electrochemical potential gradient (delta mu Na) has been evaluated in Ehrlich ascites tumor cells during accumulation of 2-aminoisobutyric acid. Cells were incubated in media of varying [Na+] (25-154 mM) in the presence of 0.25 mM 2-aminoisobutyric acid to establish maximum steady-state accumulation of the amino acid. Membrane potential (Vm) and intracellular Na+ activity (aNa) were estimated using standard electrophysiological techniques. In physiological saline ([Na+] = 154 mM) aNa is 4.4 +/- 0.6 mM, giving an apparent Na+ activity coefficient (gamma app) in the cytoplasm of 0.17 +/- 0.02. Vm under these conditions is -20.8 +/- 2.1 mV. From these values, delta mu Na = 9.9 +/- 0.8 kJ/mol. Concomitant determinations of 2-aminoisobutyric acid (AIB) accumulation show an energy requirement (delta mu AIB) of 8.5 +/- 0.5 kJ/mol. Stepwise reductions in extracellular [Na+] give parallel reductions in aNa, Vm and 2-aminoisobutyric acid accumulation. However, under all conditions tested the energy available from the Na+ electrochemical potential gradient exceeds that needed to drive 2-aminoisobutyric acid uptake. The effects of 2-aminoisobutyric acid on Vm have also been determined. Addition of AIB (10 mM) to steady-state cells leads to membrane depolarization (resting Vm = -22.1 +/- 1.3 mV; plus AIB Vm = -16.2 +/- 1.2 mV) within 1 min. Subsequent repolarization of the membrane to resting levels occurs within 10 min. The repolarization phase is blocked in the presence of ouabain (2 mM). The results establish that the energy available from the Na+ gradient is sufficient to serve as a source for 2-aminoisobutyric acid accumulation.
W D Dawson; T C Smith
Publication Detail:
Type:  Journal Article; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  Biochimica et biophysica acta     Volume:  897     ISSN:  0006-3002     ISO Abbreviation:  Biochim. Biophys. Acta     Publication Date:  1987 Feb 
Date Detail:
Created Date:  1987-03-26     Completed Date:  1987-03-26     Revised Date:  2007-11-14    
Medline Journal Info:
Nlm Unique ID:  0217513     Medline TA:  Biochim Biophys Acta     Country:  NETHERLANDS    
Other Details:
Languages:  eng     Pagination:  5-13     Citation Subset:  IM    
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MeSH Terms
Amino Acids / metabolism*,  pharmacology
Aminoisobutyric Acids / metabolism
Biological Transport, Active
Carcinoma, Ehrlich Tumor / metabolism*
Energy Metabolism
Extracellular Space / metabolism
Intracellular Fluid / metabolism
Membrane Potentials / drug effects
Mice, Inbred ICR
Sodium / physiology*
Grant Support
Reg. No./Substance:
0/Amino Acids; 0/Aminoisobutyric Acids; 62-57-7/2-aminoisobutyric acid; 7440-23-5/Sodium

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