Li⁺/Na⁺ Exchange in Trout Erythrocytes

Abstract

Previously it has been suggested that Li+/Na+ exchange is a mode of operation of Na+/H+ exchange, with arguments pro and contra. In the present experiments this question was studied by measuring Li+ effluxes from Li+ loaded trout erythrocytes under various conditions. Trout erythrocytes were loaded with Li+ by incubation in a lithium carbonate-containing solution and the efflux of Li+ was determined in both Na+-free and 150 mM Na+-containing media. The presence of Na+ enhanced the Li+ efflux. The Na+ effect was neither sensitive to amiloride nor to 5-NN-dimethylamiloride (DMA), both inhibitors of the Na+/H+ exchanger. Activation of the Na+/H+ exchanger by isoproterenol was demonstrated by an increased Li+ efflux (Li+/H+ exchange mode of the Na+/H+ exchanger). This effect was eliminated by DMA and amiloride, and by the presence of O2 which also inhibits the Na+/H+ exchanger in trout erythrocytes. However, the activation of the Li+ efflux by Na+ was not affected by O2. The finding that the stimulating effect of Na+ on Li+ efflux persists to occur in the presence of amiloride, DMA, or O2, supports the idea that the trout erythrocyte possesses a Li+/Na+ exchanger that is different from the Na+/H+ exchanger.