Modifications in the allosteric properties of phosphofructokinase in rat erythrocytes and reticulocytes cross-linked with dimethyl suberimidate and 3,3'-dithiobispropionimidate

Effects of autologous, cross-linked erythrocytes on isolated hypoperfused rabbit heart dynamics

The present study was aimed at assessing the effects of either red blood cells (RBC) or RBC cross-linked with the bifunctional dimethyl suberimidate reagent (C-RBC) on contractile force (CFo), heart rate (HR) and coronary flow (CF) of the isolated rabbit heart hypoperfused with RBC suspensions under 30 mm Hg constant pressure. RBC or C-RBC caused a rapid and marked reduction of CF, CFo and HR. In RBC-treated hearts, however, reperfusion with Tyrode solution partially restored the initial myocardial parameters, while in C-RBC-treated hearts a rapid impairment of diastolic relaxation with a subsequent, steady and increasing heart contracture was observed. Histological analysis showed that in C-RBC-perfused hearts either capillaries or precapillary arterioles were occluded by C-RBC in spite of extensive washings with Tyrode solution. These findings indicate that C-RBC impair coronary circulation markedly and irreversibly.

Oxygenation capacity of hypotonized and crosslinked rat erythrocytes

Rat erythrocytes subjected to hypotonic-isotonic dialysis, or crosslinking with bifunctional reagents (glutaraldehyde and dimethyl suberimidate hydrochloride) show a high percentage of methemoglobin and decreased oxyhemoglobin content which implies a low oxygen carrying capacity. Such modified cells maintain reversible oxygen binding properties although, they present a high hemoglobin oxygen affinity (low P50) and a diminished cooperativity in binding oxygen to hemoglobin (low n). These results suggest a reduced capacity of liberating oxygen to tissues under low PO2. Changes produced in erythrocytes can not be restored even in the presence of energy (ATP), reduced glutathione and 2,3-bisphosphoglyceric acid during the dialysis process or after crosslinking/permeabilizing treatment.

Surface properties of crosslinked erythrocytes as studied by counter-current distribution in aqueous polymer two-phase systems

The bifunctional imidoester dimethyl suberimidate hydrochloride can stabilize rat red blood cells (RBCs) by membrane protein crosslinking, and in that way they can be used as carrier systems for exogenous substances. Counter-current distribution fractionation in charge-sensitive dextran-polyethyleneglycol two-phase systems has been used to detect slight changes in surface charge in stabilized cells. A decrease in the surface charge of crosslinked RBCs and an apparent masking of the age-related cell surface properties have been found to result from the protein crosslinking. Digitonin treatment used to permeabilize crosslinked RBCs produces a significant decrease of the cell surface charge while the age-related surface properties do not seem to be modified by the treatment.

Immunoanalysis and quantitation of membrane sialoglycoproteins (glycophorins) in rat erythrocytes and reticulocytes

An enzyme-linked immunosorbent assay (ELISA) for the quantitation of rat erythrocyte membrane sialoglycoproteins (glycophorins) has been developed. Samples of erythrocytes and reticulocytes were analysed using this assay, and response compared among them and purified glycophorins samples. A broadly homologous behaviour of glycophorins was found in both cell types, suggesting the presence in reticulocytes of glycophorin molecules closely similar to those on the erythrocyte. A quantitative evaluation of glycophorins on both cell types yielded comparable levels of these glycoproteins, but with significantly higher values (1.7-fold) for reticulocytes. It is suggested that the lower number of epitopes present on the erythrocyte membrane might be due to the disappearance of some glycophorin-associated antigenic determinants during the maturation of reticulocyte to erythrocyte.

Properties of hypotonized, crosslinked and crosslinked- permeabilized rat erythrocytes as potential carrier systems

The osmotic fragility curves of isotonic rat RBCs, studied at pH 8 to avoid the Hb insolubility, are similar to those in humans at pH 7.4. Hypotonized rat RBCs, either directly or dialysed (0-24 h), are more hemolysis-resistant than isotonic rat RBCs. The discocyte-stomatocyte-spherocyte transformation can be observed with scanning electron microscopy. Protein crosslinking with dimethyl suberimidate can stabilize RBCs. The crosslinking level (60%), the cellular yield (80%), the mechanical and hemolytic resistance and the protective effect of enzyme activities, were studied in crosslinked or crosslinked- permeabilized RBCs after digitonin treatment. The normal discocytic shape of RBCs under scanning electron microscopy becomes stomatocytic in crosslinked and crosslinked- permeabilized RBCs with an erosioned surface.

Comparative kinetic behaviour and regulation by fructose-1,6-bisphosphate and ATP of pyruvate kinase from erythrocytes, reticulocytes and bone marrow cells

1. Kinetic and regulatory properties of pyruvate kinase have been studied in haemolysates of erythrocytic populations from blood and bone marrow of rats. 2. Pyruvate kinase from normal rat erythrocytes showed sigmoidal kinetics vs phosphoenolpyruvate. In contrast, the enzyme from reticulocytes and erythroid-rich bone marrow cells behaved as hyperbolic. 3. The enzyme activities were always inhibited by ATP. Activation by fructose-1,6-bisphosphate was only observed in erythrocytes. 4. These kinetic differences suggest changes in pyruvate kinase isozymes in cells of the erythrocytic line of rats.