title: 86Rb+ fluxes in Chinese hamster ovary cells as a function of membrane cholesterol content.
abstract: Steady-state fluxes of 86Rb+ (as a tracer for K+) were measured in Chinese hamster ovary cells (CHO-K1) and a mutant (CR1) defective in the regulation of cholesterol biosynthesis; the membrane cholesterol content of this mutant was varied by growing it on a range of cholesterol supplements to lipid-free medium (Sinensky, M. (1978) Proc. Natl. Acad. Sci. U.S. 75, 1247--1249). Analogous to previous findings in ascites tumor cells, 86Rb+ influx in the parent strain was differentiated into a ouabain-inhibitable 'pump' flux, furosemide-sensitive, chloride-dependent exchange diffusion, and a residual 'leak' flux. On the basis of this flux characterization, 86Rb+ pump and leak fluxes were measured in the mutant as a function of membrane cholesterol content. Pump and leak fluxes, when expressed per ml cell water, were independent of the cholesterol content of the mutant. Moreover, 86Rb+ fluxes in the mutant were equal to those in the parent strain. Our data imply that the flux behavior of K+ in the steady state is independent of the ordering of membrane lipid acyl chains.
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D002784:Cholesterol / Q000502:physiology*; D006224:Cricetinae; D005260:Female; D005665:Furosemide / Q000494:pharmacology; D007700:Kinetics; D008563:Membrane Lipids / Q000502:physiology*; D008757:Methylglucosides / Q000378:metabolism; D010042:Ouabain / Q000494:pharmacology; D010053:Ovary; D011188:Potassium / Q000378:metabolism; D012413:Rubidium / Q000378:metabolism*
chemical_list: D008563:Membrane Lipids; D008757:Methylglucosides; D010042:Ouabain; D005665:Furosemide; D002784:Cholesterol; D012413:Rubidium; D011188:Potassium