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Retention of water and potassium by erythrocytes prevents calcium-induced membrane rigidity.

Modest increases in intracellular calcium concentrations, in association with ATP depletion, cause the appearance of pathologic changes in erthrocyte shape and deformability. The loss of erythrocyte ATP and simultaneous increase in cellular calcium have previously been considered the sole requisites for the appearance of erythrocyte membrane rigidity. We report that red cells suspended in high-potassium buffers may be simultaneously loaded with calcium (through exposure to the divalent cation ionophore A23187) and depleted of ATP without incurring drastic changes in shape or in membrane stiffness. Incubation of erythrocytes under these conditions effectively blocks both water and potassium loss normally caused by calcium accumulation. However, the high external potassium has no influence on either the ionophore-induced accumulation of calcium or on the the concomitant hydrolysis of cellular ATP. These results suggest the involvement of at least one further parameter, ie, changes in cell water and cation content, in the development of calcium-induced erythrocyte rigidity.