Human red cells from prenatal hemopoiesis. Sodium/lithium exchange symmetry

Human red blood cells from prenatal stages of hemopoiesis (umbilical cord blood) and with increased lithium content were submitted to media with varying sodium concentrations in order to characterize extracellular sodium dependent-lithium efflux. On the other hand cells with different sodium contents were submitted to lithium media in order to characterize cellular sodium dependent-lithium influx through the above system. Experimental data were fitted by simple Michaelis-Menten kinetics. The Km value for lithium efflux (extracellular sodium-dependent) was significantly lower than the Km value for lithium influx (cellular sodium -dependent). The Vmax value for lithium influx was significantly greater than that for lithium efflux. The Vmax/Km ratio values were independent from the way in which the fluxes were measured. It is concluded that the simple carrier cannot be excluded as a model of the Na+-Li+ exchange system in these cells.