Effects of sodium and potassium concentrations and pH on equine erythrocyte volume and deformability

During strenuous exercise, equine erythrocyte deformability is transiently decreased. Decreased deformability is associated with increased cell volume, decreased cell density and increased intracellular sodium, potassium and chloride concentrations. To better understand these changes, we attempted to reproduce exercise-associated changes in erythrocytes in vitro by adjusting plasma sodium, potassium and pH to levels which occur during racing activity. Increasing plasma sodium to 145 meq/1 and plasma potassium to 8 meq/1 resulted in decreased erythrocyte filterability, increased cell volume, and increased intracellular sodium, potassium and chloride. Incubation of erythrocytes with frusemide and bumetanide, but not ouabain or (dihydroindenyl)oxy]alkanoic acid (DIOA), attenuated these changes. Decreasing plasma pH to 7.0 also decreased erythrocyte filterability, increased cell volume, and increased intracellular concentrations of sodium, potassium and chloride. Ouabain, but not frusemide or bumetanide, prevented the decrease infilterability and attenuated the increase in intracellular sodium. Addition of DIOA exacerbated the effect of pH on erythrocyte filterability. Therefore, exercise-associated changes in erythrocyte deformability, size and electrolyte concentration can be reproduced in vitro by increasing plasma sodium and potassium concentrations and by decreasing pH.