Background:In normal human blood, RBC volume (V), surface area (A) and hemoglobin content (H) exhibit Gaussian distributions with coefficients of variation (CV) of 10–15%. Strikingly narrower distributions are observed for their cell density (CV~0.5%) and filterability (CV~5–7%). This implies that V is highly correlated with H and A. We hypothesize that the RBC is able to adjust its volume to parameters H and A. It is tempting to speculate that intracellular free calcium (Cai) is a mediator in this process, acting as an activator of the Gardos channel. We tested this hypothesis by experimentally varying Cai and measuring changes in RBC density and filterability distributions.Material/Methods: Three different approaches were used to raise Cai: (i) RBCs were loaded with Ca2+ in the presence of the calcium ionophore A23187; (ii) RBCs were incubated with Ca2+ in the presence of 1.0 mM ortho-vanadate; and (iii) the calcium pump was switched off by ATP depletion of RBCs. The density distribution of RBCs was determined by a phthalate technique. The distributions in filterability were obtained using a kinetic filtrometer.Results: Whatever the approach used, the density and filterability distributions of treated RBCs broadened significantly in comparison with those of control cells.Conclusions: The results obtained suggest that (i) in vivo regulation of RBC volume is mediated by Cai and (ii) Cai probably depends on the A/V ratio, which determines the stress experienced by the RBC membrane in the circulation and, thereby, the calcium influx rate.

Keywords: Glucose - metabolism, Adenosine Triphosphate - metabolism, Calcimycin - pharmacology, Calcium - metabolism, Dose-Response Relationship, Drug, Erythrocytes - metabolism, Glucose - metabolism, Ionophores - pharmacology, Normal Distribution, Osmolar Concentration, Temperature, Time Factors, Vanadates - pharmacology