Shape and Volume Restoring Phenomena in Human Erythrocyte Suspension under Low Ion Strength Conditions

In this study, the earlier used method to measure the dynamics of shape changes in red blood cells (RBCs), based on an analysis of light fluctuations in the suspension, was modified to allow for the simultaneous recording of cell volume changes after appropriate recalculation of the raw absorbance and shape index data. With this improved methodology, we investigated the morphological and volume responses triggered by cell environment changes. In a low ionic strength medium (LIS), the characteristic triphasic shape changes (morphological response, MR) were accompanied with a gradual shrinking of the cells without any re-swelling phase. The addition of hyperosmotic NaCl during the terminal MR phase restored the discoid RBC shape inducing cell swelling resembling regulatory volume increase. The cell volume was greater than that before salt addition; however, it was lower than the initial isotonic cell volume. This re-swelling phase was inhibited by the external DIDS, acetozolamide and bicarbonate, and was slightly dependent upon pH ranging from 5 to 7.2. The analysis shows that chloride-induced re-swelling cannot be directly explained by the reversion of OH or HCO3 gradients which drive the Cl inside the cells against the concentration gradient, and indicates the significant role of the external bicarbonate ions in shape and volume responses in LIS.