ACTIVE TRANSPORT OF Rb⁸⁶ IN HUMAN RED CELLS AND RAT BRAIN SLICES

¹ Laboratory of General Biochemistry, University of Chile, Santiago, Chile

The use of Rb⁸⁶ as an analog of K⁺ was studied in human red cells and in brain cortex slices. In these systems, the uptake of Rb⁺ was found to follow saturation kinetics. It was demonstrated in red cells that K⁺ ions produce an inhibition of the competitive type on the uptake of Rb⁺, a requirement when two substances are transported by the same carrier. Furthermore, the values found for the K₁ for K⁺ and for the V_max for Rb⁺ are similar to those described in the literature for the K_m(K⁺) and the V_max(K⁺), respectively. Rubidium ions activated the efflux of Na²² from red cells and this effect, as well as the influx of Rb⁺1 itself, was inhibited by ouabain. In agreement with what has been reported by other authors for K⁺, sodium ions in the extracellular medium inhibited the uptake of Rb⁺ when the latter was present in low concentrations (0.2 mM). At higher concentrations of Rb⁺ (4 mM), Na⁺ activates the Rb⁺ uptake. Only part of the Na⁺-activated influx of Rb⁺ is inhibited by onabain. The possibility of an influx of Rb⁺ through pump lB and II is discussed. On the basis of these results it is coneluded that at least 90% of the Rb⁺ is transported in red cells through mechanisms that have the same characteristics as those that have been described for K⁺. In rat brain slices, Rb⁺ was actually accumulated up to 15 times in the tissue. In the presence of ouabain, the intracellular concentration of Rb⁺ reached a concentration equal to that in the incubation medium. The data presented indicate that Rb⁸⁶ can be used as an analog of K⁴² in these systems.