CHANGES IN ERYTHROCYTE CA2+-ATPASE ACTIVITY UNDER PEG-1500 AND LOW TEMPERATURE INFLUENCE

During cryopreservation different organic compounds are applied. Their introduction into cell suspension causes modification of subcellular systems and provides cell survival during freeze—thawing. The aim of the study was to determine the modifying effect of cryoprotectant PEG-1500 and low temperatures on the Ca2+-ATPase activity using the model of the saponin-permeabilized erythrocytes. PEG-1500 was found to cause the inhibition of erythrocytes Ca2+-ATPase activity despite the presence in the medium of endogenous effectors capable of stimulating the enzyme function. Modification of Ca2+-ATPase is apparently due to the physical and chemical parameters of the cryoprotectant solution since the removal of the polymer out of the medium leads to recovery of its functional properties. The reversibility of the inhibition of Ca2+-ATPase is characteristic for erythrocytes exposed to the cryoprotectant without freezing as well as for those that have been frozen and thawed in the presence of PEG-1500. The processes of freezing—thawing of cells in the cryoprotectant-free medium did not affect the Ca2+-ATPase activity indicating cryoresistance of the membrane-bond enzyme. Despite the fact that the efficiency of erythrocyte cryopreservation with PEG-1500 depends on incubation temperature prior to freezing, functional induces of Ca2+-ATPase activity in the erythrocytes exposed to PEG-1500 at 37 of 5—7 °C show no significant differences when subsequent ATP hydrolyses reaction is carried out at 37 °C. However, reduction in the temperature upon enzymatic reaction progression down to 5—7 °C after treatment of erythrocytes with PEG-1500 under similar conditions, leads to additional inhibition of enzyme activity. The identified changes in Ca2+-ATPase activity in the presence of PEG-1500 are presumably due to the modifying effect of cryoprotectant on the membrane structure and even presence of endogenous effectors in the medium cannot overcome the restrictions imposed by the modified membrane environment on this enzyme functioning.