Assay of sodium-lithium countertransport rate by direct measurement of erythrocyte lithium concentrations

An attempt to predict daily erythrocyte lithium fluctuations

Erythrocyte lithium concentration, which is a better predictor of brain lithium levels than plasma lithium concentrations, possesses the disadvantage of precise hourly determination following the last intake. The variability in RBC lithium accumulation increases as the extracellular lithium concentration increases. This increase is also time dependent and it would be very useful if the pharmacokinetic rate constant were known. Unfortunately, low lithium levels do not allow measurements within confidence intervals. In this work, we tried to determine, in vitro, the kinetic rate constants in erythrocytes of healthy volunteers. Different high lithium loaded plasma-like media were used for an extrapolation procedure of constants allowing the determination of an erythrocyte load constant namely K0 = 0.0161 +/- 0.0005 h-1 at corresponding plasma lithium concentrations. The abnormalities of lithium transport determined by in vitro procedures would be very useful in understanding the etiology of affective illness. Lithium flux pre-controls corrected with this rate constant would be very helpful in enlarging laboratory time management.

Acute inhibitory effect of alcohol on sodium-lithium countertransport

To assess a possible acute effect of environmental factors on sodium-lithium countertransport (SLC), we determined the activity of this transport system in 14 healthy volunteers, who are nonhabitual drinkers, before and 1 hour after intake of alcohol (0.8g/kg) with "Coke" as the vehicle. Alcohol significantly increased the "leak pathway" component of lithium efflux from a baseline value of 0.21 +/- 0.02 to 0.24 +/- 0.02 mmol/Lcell.h(p < 0.003); and reduced the Vmax of the transporter (0.38 +/- 0.05 to 0.31 +/- 0.04mmol/Lcell.h;p < 0.0005) without significantly changing its affinity for external sodium. The reduction in Vmax was dependent on the initial activity of the transporter (r2 = 0.5). A plot of reduction in Vmax against the product of initial Vmax value and blood alcohol level in each subject revealed a stronger relationship (r2 = 0.86), suggesting that the observed change in Vmax was also dependent on blood alcohol level. Coke alone did not change any of the parameters. We conclude that alcohol acutely inhibits SLC as well as alters erythrocyte membrane in a manner that increases passive lithium efflux.

Transmembrane in vitro and in vivo sodium-lithium countertransport in New Zealand Maori

1. Erythrocytic sodium-lithium (Na-Li) countertransport (CT) was measured in normotensive Maori and non-Maori by in vitro and in vivo methods to determine its relationship to erythrocytic hypernatraemia previously identified in Maori. 2. In vivo and in vitro CT rates were correlated within race and were similar between races. Countertransport rate was correlated with erythrocytic sodium concentration only in Maori. 3. The findings suggest the possibility of a genetically determined alteration in CT stoichiometry in Maori.

Sodium lithium countertransport is acutely influenced by heparin-induced extracorporal LDL precipitation

Sodium lithium countertransport may be a genetic marker for arterial hypertension and for the risk of diabetic nephropathy in type 1 diabetic patients. Since various factors seem to influence the transport velocity including serum lipid alterations, erythrocytes of seven patients with severe hyperlipoproteinaemia who were chronically and intermittently treated with LDL apheresis were examined before and immediately after therapy. The LDL apheresis reduced sodium lithium countertransport significantly (0.383 vs 0.269, P less than 0.02). Therefore, we conclude that serum lipid composition must be considered when interpreting sodium lithium countertransport velocity.

Diurnal variation of erythrocyte sodium-lithium countertransport rate and intracellular cation concentrations

Differences in erythrocyte sodium-lithium countertransport rate and erythrocyte potassium concentration were found between 0900 h and 2100 h in ten healthy individuals. Sodium-lithium countertransport rates were lowest at 0900 h (x: 0.34 mmol/l per h; SD: 0.15) and highest at 1200 h (x: 0.42 mmol/l per h; SD: 0.16). Erythrocyte potassium concentrations increased progressively during the day, while erythrocyte sodium concentrations did not change significantly during the day. For comparative and epidemiological studies of erythrocyte sodium-lithium countertransport rate blood samples should be taken at the same time of the day.

Whole blood storage solution for erythrocyte sodium and sodium-lithium countertransport rate determination

A solution consisting of heparinized and buffered isosmolar magnesium chloride is described in which whole blood may be stored for preservation of erythrocyte sodium (Na) and membrane sodium-lithium countertransport (Na-Li CT). Correlation (r) of fresh versus 24-h stored erythrocytes for Na was 0.990 (y = 0.30 + 0.956x) and for Na-Li CT was 0.995 (y = -0.014 + 1.022x). Na-Li CT rate was preserved in the storage solution for up to five days and erythrocyte Na concentration for at least 24 h. The solution should find application in epidemiological studies of erythrocyte Na and Na-Li CT rate in human essential hypertension as the blood specimens require no centrifugation or erythrocyte washing procedures prior to laboratory analysis.