Interrelations among Na and K content, cell volume, and buoyant density in human red blood cell populations

This study establishes a method for determining the concentration of Na and K in single red blood cells from electron probe microanalysis of a cell's Na and K content. To this end, red blood cells were separated into subpopulations according to their buoyant density by means of bovine serum density gradient centrifugation. Cell water and Na + K contents were then determined in each fraction by conventional analytic methods with cell volume estimated from measurements of hematocrits and cell number. It was found that an inverse relationship obtains between the mean cell volume and buoyant cell density since cells increased in size as density decreased. Although the amount of hemoglobin per cell was found to slightly increase as cell density decreased, hemoglobin concentration showed the inverse relationship, indicating that buoyant cell density differences are primarily the result of differences in hemoglobin concentration. In confirmation of Funder and Wieth (Funder, J., Wieth, J.O. 1966. Scand. J. Lab. Invest. 18:167-180) cell water and cell volume was found to vary directly with the summed content of Na + K. Finally, by means of electron probe microanalysis of single cells, the cellular concentration of hemoglobin was found to vary inversely with the Na + K content, providing a quantitative basis for directly estimating cell volume, and thus ionic concentration, with this technique.