Ionic and osmotic equilibria of human red blood cells treated with nystatin.

Abstract

Human red blood cells [RBC] were incubated in the presence of nystatin, allowing Na, K, Cl and pH to equilibrate rapidly when cell volume was set with external impermeant sucrose. Intracellular mean ionic activity coefficients, relative to extracellular solution values for KCl and NaCl, were 1.01 .+-. 0.02 and 0.99 .+-. 0.02 (SD, n = 10), respectively, and were independent of external pH, pHo and of [sucrose]o. With nystatin RBC volume dependence on [sucrose]o deviated from ideal osmotic behavior by as much as a factor of 3. A virial equation for .vphi., of human Hb, accounted for the cell volumes, and was the same as Adair''s measurements of .vphi.Mb for Hb isolated from sheep and ox blood. In the presence of nystatin, the slope of the acid-base titration cell curve was independent of cell volume, implying that the impermeant cellular solute charge was independent of Hb concentration at constant pH. By modifying Jacobs-Stewart equations with osmotic Hb and salt coefficients, a non-ideal thermodynamic model was devised which predicts equilibrium Donnan ratios and RBC volume from the composition of the extracellular solution and from certain cell parameters. In addition to accounting for cell volume dependence on osmotic pressure, the model also accurately describes dependence of Donnan ratios and cell volumes on pHo in the presence or absence of nystatin.