LI+ NA+ EXCHANGE IN TROUT ERYTHROCYTES

Previously it has been suggested that Li+/Na+ exchange is a mode of op eration of Na+/H+ exchange, with arguments pro and contra. In the pres ent experiments this question was studied by measuring Li+ effluxes fr om Li+-loaded trout erythrocytes under various conditions. Trout eryth rocytes were loaded with Li+ by incubation in a lithium carbonate-cont aining solution and the efflux of Li+ was determined in both Na+-free and 150 mM Na+-containing media. The presence of Na+ enhanced the Lif efflux. The Naf effect was neither sensitive to amiloride nor to 5-N,N -dimethylamiloride (DMA), both inhibitors of the Na+/H+ exchanger. Act ivation of the Na+/H+ exchanger by isoproterenol was demonstrated by a n increased Lif efflux (Li+/H+ exchange mode of the Na+/H+ exchanger). This effect was eliminated by DMA and amiloride, and by the presence of O-2 which also inhibits the Na+/H+ exchanger in trout erythrocytes. However, the activation of the Lif efflux by Na+ was not affected by O-2. The finding that the stimulating effect of Na+ on Lif efflux pers ists to occur in the presence of amiloride, DMA, or O-2, supports the idea that the trout erythrocyte possesses a Li+/Na+ exchanger that is different from the Na+/H+ exchanger.