Li<sup>+</sup>/Na<sup>+</sup> 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 m<i>M</i> 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.