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

Dietary electrolytes and urinary natriuretic factors

We examined the relationship between the excretion of electrolytes (sodium, potassium and calcium), dopamine and digoxin-like immunoreactive substance in 41 young healthy female subjects (age 18-23 years) in order to study the interaction of electrolyte intake on dopamine and digoxin-like immunoreactive substance--factors which have been postulated to have a pathogenic role in hypertension. Sodium excretion was significantly correlated with dopamine excretion (r = 0.545, P < 0.0005) and digoxin-like immunoreactive substance (r = 0.359, P < 0.02). There was also a significant correlation between calcium and digoxin-like immunoreactive substance (r = 0.345, P < 0.03). Stepwise multiple regression analysis further confirmed that sodium is the only contributor to dopamine excretion and calcium is the only contributor to digoxin-like immunoreactive substance (r2 = 0.114). We conclude that in young healthy subjects dopamine excretion is determined partly by sodium intake and that the excretion of digoxin-like immunoreactive substance is independent of sodium intake.

A rapid assay for the measurement of Na+,K(+)-ATPase inhibitors

A rapid and automated assay for inhibitors of Na+, K(+)-ATPase was developed by determining the amount of inorganic phosphorus (Pi) released by Na+,K(+)-ATPase in a centrifugal analyzer. This method avoids long incubation, strong acids and centrifugation as in the conventional manual method. The coefficients of variation of intra- and inter-assay at ouabain concentration 0.5 mumol/L were 1.0 and 1.4%, respectively. The method is quick, reproducible and easy compared with current techniques.

Erythrocyte sodium-lithium countertransport in Chinese: its relationship to family history of hypertension

Rates of sodium (Na+)-stimulated lithium (Li+) efflux (Na(+)-Li+ countertransport) and ouabain-sensitive Na+ efflux (Na+ pump) were determined in erythrocytes of Chinese normotensive and hypertensive subjects. Near-maximal rate of Na(+)-Li+ countertransport was found to be significantly higher in hypertensive than normotensive subjects. No significant difference was observed for the rate of Na+ pump between them. A second series of study involved normotensive subjects without and with hypertensive parent(s) (group A and B, respectively) and hypertensive subjects (group C). We found that the rate of Na(+)-Li+ countertransport in group A was significantly lower than that of group B and C, while no difference existed between group B and C. No significant difference was observed for the rate of Na+ pump among the three groups. Our results suggested that Na(+)-Li+ countertransport activity could be a genetic marker for essential hypertension in Chinese, similar to that as proposed in Caucasians.

Ouabain-binding sites of reticulocytes from guinea pigs treated with triiodothyronine

To understand the mechanism of reduced number of sodium pump units (ouabain-binding sites, OBS) of erythrocytes in hyperthyroidism, OBS of reticulocytes from guinea pigs injected with triiodothyronine (T3) were measured. Reticulocytosis was induced in 16 guinea pigs by withdrawing 6 to 10 mL of blood for 5 days followed by 2 days rest. T3 (50 micrograms/100 g body weight) was injected into seven animals on days 4 and 6, and the remainder were injected with solvent for T3. Reticulocyte-rich blood was withdrawn on day 8. Oxygen consumption determined 24 hours after the first injection of T3 was 30% higher in the T3-treated animals (P less than .001). OBS of reticulocytes from control animals were sixfold higher than that of mature erythrocytes. Reticulocytes from T3-treated guinea pigs had significantly lower OBS (P less than .01) compared with controls. We conclude that the loss of OBS induced by thyroid hormones probably occurs during the formation of reticulocytes.