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.