The Na+/H+ Exchanger Present in Trout Erythrocyte Membranes is Not Responsible for the Amiloride-insensitive Na+/Li+ Exchange Activity

Autor: van Norren, K., Gorissen, R., Borgese, F., Borggreven, J.M.P.M., De Pont, J.J.H.H.M.
Zdroj: Journal of Membrane Biology; 19971201, Vol. 160 Issue: 3 p193-199, 7p
Abstrakt: Abstract.: The protein responsible for the Na+/Li+ exchange activity across the erythrocyte membrane has not been cloned or isolated. It has been suggested that a Na+/H+ exchanger could be responsible for the Na+/Li+ exchange activity across the erythrocyte membrane. Previously, we reported that in the trout erythrocyte, the Li+/H+ exchange activity (mediated by the Na+/H+ exchanger βNHE) and the Na+/Li+ exchange activity respond differently to cAMP, DMA (dimethyl-amiloride) and O2. We concluded that the DMA insensitive Na+/Li+ exchange activity originates from a different protein. To further examine these findings, we measured Li+ efflux in fibroblasts expressing the βNHE as the only Na+/H+ exchanger. Moreover, the internal pH of these cells was monitored with a fluorescent probe. Our findings indicate that acidification of fibroblasts expressing the Na+/H+ exchanger βNHE, induces a Na+ stimulated Li+ efflux activity in trout erythrocytes. This exchange activity, however, is DMA sensitive and therefore differs from the DMA insensitive Na+/Li+ exchange activity. In these fibroblasts no significant DMA insensitive Na+/Li+ exchange activity was found. These results support the hypothesis that the trout erythrocyte Na+/Li+ exchange activity is not mediated by the Na+/H+ exchanger (βNHE) present in these membranes.
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