Calcium-induced erythrocyte rigidity: the roles of cellular metabolism, hydration, and ionic balance.

Previous investigations have shown that incubation of human erythrocytes with the ionophore A23187 and calcium causes accumulation of the cation, losses in potassium, water, and cellular volume, hydrolysis of adenosine triphosphate (ATP), conversion of biconcave discocytes to echinocytes and spheroechinocytes, and marked increases in erythrocyte resistance to micropipette aspiration. Subsequent studies demonstrated that prevention of water and potassium loss blocked the influence of calcium loading on erythrocyte stiffness without affecting calcium uptake by the cells or hydrolysis of ATP. In the present study erythrocytes were exposed to conditions that permitted individual or coordinate manipulation of cellular ATP, water, potassium, and calcium in order to determine which factors developing as a result of calcium loading were responsible for the calcium-induced changes in erythrocyte viscoelastic properties. Results of the study demonstrate that volume loss, ATP hydrolysis, and potassium depletion do not individually or in combination cause increases in erythrocyte stiffness. However, all of these changes are essential and must develop in conjunction with calcium loading in order for erythrocytes to develop diminished deformability and elasticity.