51. The Na+/H+ Exchanger Present in Trout Erythrocyte Membranes is Not Responsible for the Amiloride-insensitive Na+/Li+ Exchange Activity
- Author
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van Norren, K., Gorissen, R., Borgese, F., Borggreven, J.M.P.M., and De Pont, J.J.H.H.M.
- Abstract
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.- Published
- 1997
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