Rearrangement of erythrocyte band 3 molecules and reversible formation of osmotic holes under hypotonic conditions

Non-oxidative band-3 clustering agents cause the externalization of phosphatidylserine on erythrocyte surfaces by a calcium-independent mechanism

Aging of red blood cells (RBCs) is associated with alteration in a wide range of RBC features, occurring each on its own timescale. A number of these changes are interrelated and initiate a cascade of biochemical and structural transformations, including band-3 clustering and phosphatidylserine (PS) externalization. Using specific band-3 clustering agents (acridine orange (AO) and ZnCl₂), we examined whether treatment of RBCs with these agents may affects PS externalization and whether this process is Ca²⁺-dependent. RBCs were isolated from the blood of eight healthy donors upon obtaining their informed consent. The suspension was supplemented with increasing concentrations of AO or ZnCl₂ (from 0.5 to 2.0 mM) and incubated at 25 °C for 60 min. To detect PS at the RBC surface, we used allophycocyanin-conjugated recombinant human Annexin V. We demonstrated, that treatment of RBCs with both clustering agents caused an elevation in the percent of cells positively labeled by Annexin-V (RBC^PS), and that this value was not dependent on the presence of calcium in the buffer: RBCs treated with AO in the presence of either EDTA, EGTA or calcium exhibited similar percentage of RBC^PS. Moreover, the active influx of Zn²⁺ into RBCs induced by their co-incubation with both ZnCl₂ and A23187 did not increase the percent of RBC^PS as compared to RBCs incubated with ZnCl₂ alone. Taken together, these results demonstrate that the band-3 clustering agents (AO or ZnCl₂) induce PS externalization in a Ca²⁺ independent manner, and we hereby suggest a possible scenario for this phenomenon.

Thermal sensitivity and haemolysis of erythrocytes with membranopathy

Measuring the impedance of heated suspensions of erythrocytes and erythrocyte ghost membranes, two thermally-induced alterations are registered in the plasma membrane at T_A (denaturation of spectrin with inducing temperature at 49,5 °C) and T_G (hyperthermic activation of basal ion permeability with inducing temperature at 60.7 °C). In this study erythrocytes from 9 healthy patients and 15 patients with hemolytic anemia were studied and divided into four groups depending on their T_A and T_G top temperatures. The T_A and T_G of erythrocytes with hemoglobinopathy were the same as those of control erythrocytes while those of erythrocytes with membranopathy were significantly reduced. In erythrocytes with severe membranopathy, the T_G was decreased by about 5 °C. In latter cells the normal value of T_G was restored and the resistance to thermal haemolysis was increased by 90% after the specific stabilization of band 3 protein by 4,4'-diisothiocyanato-stilbene-2,2'-disulfonic acid (DIDS). Obtained results indicate the involvement of band 3 in the membrane alteration at T_G and in the heat target responsible for thermal haemolysis.

Cycling Exercise Training Alleviates Hypoxia-Impaired Erythrocyte Rheology

PURPOSE

Physical exercise or hypoxic exposure influences hemorheology and acid-base homeostasis. Band 3 protein in erythrocytes modulates cells' rheological properties and anion transport ability. This study investigated how cycling aerobic interval training (AIT) and moderate continuous training (MCT) affect the rheological function and band 3 activity of erythrocytes under hypoxic exercise (HE) stress.

METHODS

Forty-five healthy sedentary men were randomized to engage in either AIT (3-min intervals at 40% and 80% of VO2max, n = 15) or MCT (sustained 60% of VO2max, n = 15) on a bicycle ergometer for 30 min · d(-1) (5 d · wk(-1) for 5 wk) or to a control group that did not perform any exercise (n = 15). Erythrocyte rheological responses to HE (100 W under 12% O2 for 30 min) were determined before and after various regimens.

RESULTS

Acute HE increased the aggregation and osmotic fragility of erythrocytes, decreased the deformability of erythrocytes, and depressed erythrocyte band 3 activity, as indicated by lowered anion transport ability. Following 5 wk of intervention, the AIT group exhibited maximal work rate and VO2max higher than those in the MCT and control groups. Moreover, cycling AIT and MCT diminished the extent of erythrocytes' enhanced aggregation and osmotic fragility and reduced their deformability and band 3 activity caused by HE. Additionally, erythrocyte band 3 activity was directly related to erythrocyte deformability and inversely related to erythrocyte aggregation and osmotic fragility.

CONCLUSIONS

Cycling AIT is superior to cycling MCT in enhancing aerobic capacity. Moreover, either cycling AIT or MCT effectively alleviates HE-evoked impairments of erythrocyte rheological characteristics and band 3 function.

Hemolysis by surfactants--A review

An overview of the use of surfactants for erythrocyte lysis and their cell membrane action mechanisms is given. Erythrocyte membrane characteristics and its association with the cell cytoskeleton are presented in order to complete understanding of the erythrocyte membrane distortion. Cell homeostasis disturbances caused by surfactants might induce changes starting from shape modification to cell lysis. Two main mechanisms are hypothesized in literature which are osmotic lysis and lysis by solubilization even if the boundary between them is not clearly defined. Another specific mechanism based on the formation of membrane pores is suggested in the particular case of saponins. The lytic potency of a surfactant is related to its affinity for the membrane and the modification of the lipid membrane curvature. This is to be related to the surfactant shape defined by its hydrophobic and hydrophilic moieties but also by experimental conditions. As a consequence, prediction of the hemolytic potency of a given surfactant is challenging. Several studies are focused on the relation between surfactant erythrolytic potency and their physico-chemical parameters such as the critical micellar concentration (CMC), the hydrophile-lipophile balance (HLB), the surfactant membrane/water partition coefficient (K) or the packing parameter (P). The CMC is one of the most important factors considered even if a lytic activity cut-off effect points out that the only consideration of CMC not enough predictive. The relation K.CMC must be considered in addition to the CMC to predict the surfactant lytic capacity within the same family of non ionic surfactant. Those surfactant structure/lytic activity studies demonstrate the requirement to take into account a combination of physico-chemical parameters to understand and foresee surfactant lytic potency.

Erythrocyte swelling and membrane hole formation in hypotonic media as studied by conductometry

Hypoosmotic swelling of erythrocytes and the formation of membrane holes were studied by measuring the dc conductance (G). In accordance with the theoretical predictions, these processes are manifested by a decrease in G followed by its increase. Thus, unlike the conventional osmotic fragility test, the proposed methodological approach allows investigations of both the kinetics of swelling and the erythrocyte fragility. It is shown that the initial rate of swelling and the equilibrium size of the cells are affected by the tonicity of a hypotonic solution and the membrane rheological properties. Because the rupture of biological membranes is a stochastic process, a time-dependent increase in the conductance follows an integral distribution function of the membrane lifetime. The main conclusion which stems from reported results is that information about rheological properties of red blood cell (RBC) membranes and the resistivity of RBCs to a certain osmotic shock may be extracted from conductance signals.