The Na+/H+ exchanger present in trout erythrocyte membranes is not responsible for the amiloride-insensitive Na+/Li+ exchange activity.
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 beta NHE) 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 beta NHE 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 beta NHE, 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 (beta NHE) present in these membranes.
van Norren
K
K
Department of Biochemistry, University of Nijmegen, The Netherlands.
Gorissen
R
R
Borgese
F
F
Borggreven
J M
JM
De Pont
J J
JJ
D000584:Amiloride / Q000494:pharmacology*; D000818:Animals; D006224:Cricetinae; D004910:Erythrocyte Membrane / Q000187:drug effects* / Q000378:metabolism*; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D017136:Ion Transport / Q000187:drug effects*; D008094:Lithium / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers / Q000187:drug effects*; D014337:Trout
D017923:Sodium-Hydrogen Exchangers; D000584:Amiloride; D008094:Lithium