Ouabain-binding and 86rubidium-uptake in lymphocytes of normal and borderline hypertensive subjects

Increased number of ouabain binding sites in lymphocytes from borderline hypertensives

Lymphocytes were used as a cellular model for the in vitro measurements of maximal ouabain binding sites in order to assess any changes in young men at increased risk of developing essential hypertension, and to analyse whether any such changes were associated to borderline hypertension and/or heredity. Four groups were evaluated; 28 normotensive (NTO) and 20 borderline hypertensive (BHO) offspring of hypertensives. Twelve borderline hypertensives (BH) and 28 normotensive subjects (NT) with normotensive parents. The number of ouabain binding sites were significantly increased in the borderline hypertensives irrespective of heredity. The borderline hypertensives were heavier than the normotensives. A stepwise multiple regression model was therefore used in order to control confoundings by body mass index (BMI) and other factors such as age, gamma glutamyl transferase, 24 h sodium excretion, serum triglyceride, and serum cholesterol, which may influence the number of ouabain binding sites. Only BMI entered the stepwise model. These results indicate the presence of an increased number of sodium-potassium pumps in lymphocytes from borderline hypertensives. This difference may be attributed to the blood pressure disease or increased body mass.

3H-Ouabain binding to human mononuclear leucocytes

Specific binding of cardiac glycosides to intact human blood cells may be a suitable model for physiological or disease-induced changes in cardiac glycoside binding to human heart muscle. Since the erythrocyte contains no nucleus and has relatively few binding sites compared with heart muscle, intact mononuclear leucocytes were investigated in the present study. Using leucocyte suspensions from 34 normal subjects, 133 measurements of 3H-ouabain binding-were obtained. 3H-Ouabain bound to one type of binding site with an affinity (KD) of 2.8 +/- 1.2 X 10(-9) M, similar to that of human heart muscle. Association and dissociation were slow processes (k+1, 3.9 X 10(4) M-1 sec-1; k-1, 8.1 X 10(-5) sec-1, n = 2). The number of ouabain binding sites/leucocyte varied from 18,000 to 60,000 (mean +/- SD, 34,600 +/- 9,700), with no correlation with the proportion of monocytes present or with the serum K+-level of the donors. Large inter- and intra-individual differences in binding site number were measured which are probably a result of the heterogeneity of the cell suspension used. Thus, the ouabain binding site on human heart muscle and intact mononuclear leucocytes is probably identical. However, the number of binding sites in mixtures of mononuclear leucocytes shows large and inconsistent intraindividual variations, making these studies unsuitable for quantifying drug- or disease-induced changes in ouabain binding site number.