Characterization of Ca2+,Mg2+-ATPase of blood lymphocytes in women with ovarian cancer

Ionized Ca2+ is crucial for regulation of practically all intracellular processes, including tumor growth, cell proliferation, apoptosis, etc. The plasma membrane Ca2+, Mg2+-ATPase plays an important role in maintaining intracellular Ca2+ homeostasis. The function of this enzyme is to reduce the Ca2+ concentration in the cytosol, namely its transport against a concentration gradient in the extracellular medium. We have investigated the activity of plasma membrane Ca2+, Mg2+-ATPase of lymphocytes of practically (clinically) healthy women of different age groups and also patients with ovarian cancer stage III and IV. It was found that the enzyme activity in women of the older age group was not significantly reduced in relation to the activity of the younger age group. Thus, the value of the maximum rate of ATP hydrolysis by plasma membrane Ca2+, Mg2+-ATPase of blood lymphocytes in practically healthy women under the conditions of physiological norm was 1.1 times higher than under of pre-nosological state. In patients with ovarian cancer (stages III and IV), plasma membrane Ca2+, Mg2+-ATPase activity of blood lymphocytes significantly differed from the physiological norm and decreased by 1.6 and 1.8 times, compared with the physiological norm. The decrease of the plasma membrane Ca2+, Mg2+-ATPase activity of blood lymphocytes in patients with ovarian cancer indicates an increase of Ca2+ in the cytosol of lymphocytes. Determination of affinity constants showed that these values were in the submillimolar range of concentration, corresponding to the physiological concentration in the cell cytoplasm (0.5-5.0 mM). In healthy persons, under the condition of physiological norm, the affinity constant of plasma membrane Ca2+, Mg2+-ATPase to the ATP was 0.16 +/- 0.02 mM and at pre-nosological state -0.19 +/- 0.02 mM. The affinity constant of plasma membrane Ca2+, Mg2+-ATPase of lymphocytes to ATP in patients with ovarian cancer (stage III) was 0.32 +/- 0.03 mM and with ovarian cancer (stage IV) 0.35 +/- 0.03 mM. That is, the affinity constant of plasma membrane Ca2+, Mg2+-ATPase of lymphocytes to ATP in patients with ovarian cancer was 2.0-2.1 times higher than this value for the blood lymphocytes in the control group (physiological norm). The kinetic analysis of Ca(2+)activated, Mg2+-dependent hydrolysis of ATP in blood lymphocytes in women showed that the decrease in the activity of Ca2+, Mg2+-ATPase was due to a decrease in the affinity of the enzyme to the substrate (KATP increases 2-fold).