Intracellular pH regulation of SV-40 virus transformed human MRC-5 fibroblasts and cell membrane cholesterol.
Alterations in membrane cholesterol could affect the activity of various membrane transporters, including the Na(+)-H+ antiport. The effect of cellular cholesterol depletion (with phosphatidylcholine liposomes) and enrichment (with cholesterol and phosphatidylcholine liposomes) on cellular pH regulation was studied in SV-40 virus transformed human MRC-5 fibroblasts. Cellular cholesterol depletion led to activation of the Na(+)-H+ antiport by an increased maximal velocity (Vmax) of the transporter, with no changes in the apparent dissociation constant (Kd) or Hill coefficient for intracellular H+. Cholesterol enrichment had no effect on the activation of the Na(+)-H+ antiport by intracellular acidosis. However, activation of the Na(+)-H+ antiport by an osmotic stimulus was enhanced in cholesterol-depleted cells and reduced in cholesterol-enriched cells. Liposomes that had no effect on cellular cholesterol did not alter the activation of Na(+)-H+ antiport activity by intracellular acidosis or an osmotic stimulus. Thus in situ modification of cellular cholesterol altered Na(+)-H+ antiport activity differently depending on the type of activating stimulus.
Department of Pharmacology, Leicester Royal Infirmary, United Kingdom.
L L
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Ng
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Delva
J E
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Davies
D002352:Carrier Proteins / Q000378:metabolism; D002461:Cell Line, Transformed; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism*; D002472:Cell Transformation, Viral; D002784:Cholesterol / Q000378:metabolism*; D005347:Fibroblasts; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007424:Intracellular Fluid / Q000378:metabolism; D007700:Kinetics; D008081:Liposomes / Q000494:pharmacology; D008563:Membrane Lipids / Q000378:metabolism*; D013539:Simian virus 40 / Q000235:genetics*; D017923:Sodium-Hydrogen Exchangers; D013395:Sucrose / Q000494:pharmacology
D002352:Carrier Proteins; D008081:Liposomes; D008563:Membrane Lipids; D017923:Sodium-Hydrogen Exchangers; D013395:Sucrose; D002784:Cholesterol