The changes in erythrocyte Ca-ATPase activity induced by PEG-1500 and low temperatures.

Various organic compounds are applied upon cryopreservation and their adding into cell suspension causes modification of subcellular systems, providing cell survival during freeze-thawing. The aim of the study was to assess the modifying effect of cryoprotectant PEG-1500 and low temperatures on Ca-ATPase activity in saponin-permeabilized erythrocytes. PEG-1500 was revealed to inhibit erythrocyte Ca-ATPase activity despite the presence of endogenous effectors able to stimulate the enzyme function. Presumably, the Ca-ATPase modification was determined by the physicochemical properties of the polymer solution, since the removal of PEG-1500 out of the medium recovered the enzyme activity. Reversibility of Ca-ATPase inhibition was characteristic of erythrocytes both exposed to cryoprotectant without freezing and frozen-thawed in the PEG-1500 presence. The cell freeze-thawing without cryoprotectant had no effect on Ca-ATPase, suggesting that membrane form of enzyme is cryoresistent. Although the efficiency of erythrocyte cryopreservation with PEG-1500 depends on the incubation temperature before freezing stage, the functional indices of Ca-ATPase in erythrocytes exposed to PEG-1500 at 37 and 5-7°C had no significant distinctions if the subsequent ATP hydrolysis was conducted at 37°C. However, the enzyme activity was additionally slowed down when the temperature of enzymatic reaction was decreased to 5-7°C after erythrocyte preincubation with PEG-1500 under the same conditions. The identified changes in Ca-ATPase activity in erythrocytes in the PEG-1500 presence were most likely determined by a modifying effect of the cryoprotectant on the membrane structure; as a result, the Ca-ATPase endogenous effectors present in the medium could not overcome the restrictions imposed on the enzyme function by a modified membrane macroenvironment. [ABSTRACT FROM AUTHOR]