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Human red blood cells (RBCs) when suspended in a Low Ionic Strength medium (LIS) demonstrate characteristic triphasic shape changes (morphological response, MR) and become reduced in volume. Tahitian Tabari Noni juice (Tb), after being given during the terminal phase of MR, was shown to initiate an unusual cell response. This response can be described as a volumetric four-phasic response including first a shrinking phase, attributed to the initial sucrose-induced shrinkage during typical MR, a rapid first swelling phase, induced by application of the juice, followed spontaneously by the occurrence of a more prolonged second shrinking phase, which culminated in the swelling and hemolysis of the cells. All the phases of volumetric response can be independently regulated by chloride, DIDS, cations Ca2+, Ag+, Hg2+ or plasma. The second shrinking phase is not inhibited by clotrimazole, a known inhibitor of Gardos channels, and can be replicated by a mixture of two ionophores (valinomycin and CCCP), suggesting the involvement of the putative K+/H+ exchanger as a mechanism of this phase. We suggest that the erythrocyte membrane is equipped with additional molecular systems, poorly characterized at present, that regulate the cell shape and volume. The cell should, therefore, be considered as an “active” responsive system instead of a “passive” osmometer-like structure.

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.