Modulation of Human Erythrocyte Ca²⁺-ATPase Activity by Glycerol: The Role of Calmodulin

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N. G. Zemlyanskikh^* and O. A. Kofanova

Institute for Problems of Cryobiology and Cryomedicine, National Academy of Sciences of Ukraine, Pereyaslavskaya str. 23, 61015 Kharkov, Ukraine; fax: (805) 737-33084; E-mail: cryo@online.kharkov.ua

^* To whom correspondence should be addressed.

Received September 15, 2005; Revision received March 23, 2006

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The effect of an intracellular cryoprotectant glycerol on human erythrocyte Ca²⁺-ATPase activity and possible involvement of calmodulin in the regulation of Ca²⁺-pump under these conditions were investigated. The experiments were carried out using saponin-permeabilized cells and isolated erythrocyte membrane fractions (white ghosts). Addition of rather low concentrations of glycerol to the medium increased Ca²⁺-ATPase activity in the saponin-permeabilized cells; the maximal effect was observed at 10% glycerol. Subsequent increase in glycerol concentrations above 20% was accompanied by inhibition of Ca²⁺-ATPase activity. Lack of stimulating effect of glycerol on white ghost Ca²⁺-ATPase may be attributed to removal of endogenous compounds regulating activity of this ion transport system. Inhibitory analysis using R24571 revealed that activation of Ca²⁺-ATPase by 10% glycerol was observed only in the case of inhibitor administration after modification of cells with glycerol; in the case of inhibitor addition before erythrocyte contact with glycerol, this phenomenon disappeared. These data suggest the possibility of regulation of human erythrocyte Ca²⁺-ATPase by glycerol; this regulatory effect may be attributed to both glycerol-induced structural changes in the membrane and also involvement of calmodulin in modulation of catalytic activity of the Ca²⁺-pump.

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KEY WORDS: erythrocyte, Ca²⁺-ATPase, calmodulin, glycerol

DOI: 10.1134/S0006297906080128

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