Role of Na+/Ca2+ exchanger in preventing Na+ overload and hepatocyte injury: opposite effects of extracellular and intracellular Ca2+ chelation.
We have previously shown that an increase of intracellular Na+ occurs in isolated rat hepatocytes undergoing ATP depletion and that Na+ accumulation is associated with an uncontrolled influx of Ca2+ through the activation in reverse mode of the Na+/Ca2+ exchanger. In the present study we have investigated the relationship between alterations of Na+ and Ca2+ homeostasis and hepatocyte killing using treatments which differentially chelate extracellular or intracellular Ca2+. Chelation of extracellular Ca2+ by ethylene glycol bis-(beta-aminoethyl ether) N,N,N',N'-tetraacetic acid (EGTA) potentiated Na+ overload and cell killing induced in isolated rat hepatocytes by hypoxia or menadione. Similar effects were also observed when Na+ accumulation was induced by the combined addition of Na+ ionophore monensin and the inhibition of plasma membrane Na+/K+ ATPase by ouabain. Conversely, the use of the intracellular Ca2+ chelator EGTA acetoxymethyl ester (EGTA/AM) reduced Na+ overload and hepatocyte death induced by hypoxia or cell treatment with menadione or monensin plus ouabain. The effects of EGTA/AM were reverted in the presence of bepridil, an inhibitor of Na+/Ca2+ exchanger. Altogether these results indicated that differential chelation of intracellular or extracellular Ca2+ influences in opposite ways hepatocyte killing due to ATP depletion by modulating intracellular Na+ levels through the reversed activity of the Na+/Ca2+ exchanger.
Carini
R
R
Department of Medical Sciences, University of Torino, Turin, Italy.
de Cesaris
M G
MG
Bellomo
G
G
Albano
E
E
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism*; D002614:Chelating Agents; D005110:Extracellular Space; D008099:Liver / Q000378:metabolism* / Q000473:pathology; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D012964:Sodium / Q000378:metabolism*; D019831:Sodium-Calcium Exchanger
D002352:Carrier Proteins; D002614:Chelating Agents; D019831:Sodium-Calcium Exchanger; D012964:Sodium; D002118:Calcium