A kinetic expression for sodium-lithium countertransport in human red cells

Sodium-lithium counter-transport in human red blood cells may be a potentially useful measurement in studies of hypertension. A kinetic expression describing this counter-transport was derived and evaluated using red cells from nine subjects at various concentrations of intracellular and extracellular Li+ and Na+. The countertransport is dependent upon all four concentrations, intracellular Li+ and Na+ as well as extracellular Li+ and Na+. We confirm that the maximum Na+-Li+ counter-transport (Vmax) is a property of the individual cells while the half-maximal saturating concentrations (K 1/2) for Li+ and Na+ are the same for all subjects. This expression permits a more thorough understanding of conditions affecting Na+-Li+ countertransport measurement.