More on sodium-potassium-ATPase and obesity

Determinants of salt sensitivity in black and white normotensive and hypertensive women

Salt sensitivity (SS) has been linked to human hypertension. We examined ethnic differences in the relation between SS; erythrocyte sodium (Na+i), calcium (Ca2+i), potassium (K+i), and magnesium (Mg2+i); and sodium pump activity in African-American (AA) and white women. In a crossover protocol, similar numbers of normotensive, hypertensive, AA, and white women were randomized to 7 days of a 20 meq/d and a >200 meq/d salt diet (n=199). After an overnight inpatient stay, group differences in supine blood pressure (BP), heart rate, erythrocyte cations, and sodium pump activity were measured. The prevalence of SS (53.5% vs 51%) and salt resistance (26.3% vs 30.0%) was similar in both races. Greater mean BP increase with salt loading was seen in AA vs white hypertensives but not between the normotensive women. In hypertensives, increase in mean arterial pressure was 12.6 vs 8.2 mm Hg in AAs vs whites, respectively (P<0.01), and for systolic BP, it was 23 vs 14.8 mm Hg (P<0.01). Higher Na+i and Ca2+i were noted in SS and salt-intermediate AA than in the corresponding white subjects. Na+i, Ca2+i, and the ratios of Na+i to K+i and of Ca2+i to Mg2+i were positively correlated with salt responsiveness in AA but not in white women. Sodium pump activity was similar between groups, although the change in maximal activity trended to vary inversely with SS in AA. In closely matched AA and white women, the prevalence of SS is similarly high in both races, although the magnitude of BP increase is greater in AA hypertensives. In AA but not in whites, SS is positively associated with Na+i, Ca2+i, and the ratios of Na+i to K+i and of Ca2+i to Mg2+i.

Erythrocyte sodium-potassium pump in thyrotoxic periodic paralysis

To search for a genetic marker in patients with thyrotoxic periodic paralysis (TPP), we studied the erythrocyte sodium-potassium pump activity in 13 patients with TPP; 30 thyrotoxic patients with no history of paralysis (T) and 69 euthyroid controls. In thyrotoxic patients (TPP and T), erythrocyte ouabain binding and ouabain sensitive sodium efflux rate constant were decreased while erythrocyte sodium content was increased. All these changes reverted to normal when the patients became euthyroid. Maximal ouabain binding capacity correlated positively with ouabain sensitive sodium efflux rate constant (r = 0.542; p less than 0.001; n = 155) and negatively with serum thyroxine concentration (r = -0.571; p less than 0.001; n = 60) and erythrocyte sodium content (r = -0.521; p less than 0.001; n = 155). In the thyrotoxic state, maximal ouabain binding capacity was just significantly higher in TPP when compared with T (0.268 +/- 0.014 and 0.234 +/- 0.009 pmol/10(9) cells respectively; p less than 0.05). This difference could not be demonstrated when the patients became euthyroid. Our findings suggest that patients with TPP respond to thyrotoxicosis with a smaller decrement in erythrocyte sodium-potassium ATPase activity than patients without a history of paralysis. However, the difference is too small to represent a useful genetic marker for this disease entity

Profile of systemic hypertension in black patients

Hypertension extracts a huge toll from the black community in terms of excess morbidity and mortality. The black hypertensive is more likely to die from the disease and to have stroke, end-stage renal disease or heart failure. Furthermore, contrary to previous beliefs, blacks are at least as likely to have coronary artery disease as whites. Although substantial overlap occurs, the black hypertensive is more likely to be volume-expanded, to have a lower plasma renin level, and to be classified, as salt-sensitive than is the white hypertensive. Decreased dietary potassium and calcium intake, altered intra-cellular handling of sodium and calcium, and psychosocial factors have also been implicated in the pathophysiology of hypertension in blacks.

The effect of oral glucose on the leucocyte sodium pump in normal and obese subjects

The effect of oral glucose (40 g/m2 body surface area) on the leucocyte 22Na efflux rate constants (ERC) was studied in 13 normal weight and 10 obese subjects. The ouabain-sensitive 22Na ERC was higher in leucocytes isolated from fasting obese subjects (median [range] for obese 2.77 [2.33-3.11] vs normals 1.91 [1.57-2.77] h-1, P less than 0.001). There was no difference in the ouabain-resistant 22Na ERC. Oral glucose raised the ouabain-sensitive 22Na ERC after 2 h in normal subjects (1.91 [1.57-2.77] to 2.41 [2.11-3.02] h-1, P less than 0.001). The ouabain-resistant 22Na ERC fell from 0.71 [0.32-1.10] to 0.46 [0.35-0.68] h-1, P less than 0.008. Conversely, in obese subjects, the ouabain-sensitive ERC fell (2.77 [2.33-3.11] to 2.59 [2.11-2.92] h-1, P less than 0.06). There was no significant change in ouabain-resistant 22Na ERC 2 h after oral glucose. The fasting leucocyte 22Na ouabain-sensitive ERC correlated with fasting plasma insulin levels and insulin resistance (rs = 0.48, P less than 0.01 for both). The change in this ERC with oral glucose correlated with the incremental insulin response over 2 h (rs = -0.53, P less than 0.006) and to the insulin resistance (rs = -0.56, P less than 0.003). The failure of oral glucose to stimulate the leucocyte sodium pump in obesity could partially account for the defect in dietary thermogenesis in obesity. This defect in stimulation of the sodium pump is related to insulin resistance.

Differences in erythrocyte cation (sodium) transport between Chinese and non Chinese males

Erythrocyte sodium content, sodium pump activity (ouabain sensitive efflux rate, efflux rate constant, ouabain binding sites and Na+, K+-ATPase activity), sodium-lithium countertransport and sodium-potassium cotransport activities were measured in 10 European males, 11 non Chinese Asian males and 12 Chinese males. There were no differences between the 3 groups in any of the measurements of active transport. The sodium-lithium countertransport was higher and sodium-potassium cotransport (measured as lithium-potassium cotransport) was lower in Chinese compared to either the Europeans or non Chinese Asians. There were no differences in counter and cotransport activities between the Europeans and non Chinese Asians. Multiple regression analysis showed that the co and countertransport pathways contribute little to the maintenance of erythrocyte sodium content in healthy subjects.