Molecular cloning and functional expression of a rat Na+/H+ exchanger (NHE5) highly expressed in brain

We report here the cloning, primary structure, heterologous expression, tissue distribution, and localization of a cDNA encoding rat NHE5, a fifth member of the mammalian plasma membrane Na+/H+ exchanger (NHE) gene family. The full-length open reading frame as well as 34 nucleotides of 5'-untranslated and 1443 nucleotides of 3'-untranslated sequences were obtained using a polymerase chain reaction strategy involving reverse transcription-polymerase chain reaction and 5'/3'-rapid amplification of cDNA ends. The NHE5 cDNA encodes a protein of 898 amino acids with a calculated M-r of 99,044 and is predicted to contain 11-13 transmembrane domains. An amino acid comparison of the coding region of rat NHE5 reveals 95% identity with human NHE5. Northern hybridization analysis showed that high level expression of NHE5 mRNA is restricted to brain. Transfection of the coding region of rat NHE5 into NHE-deficient PS120 cells resulted in Na+/H+ exchange activity that was relatively insensitive to the amiloride analogue, 5-(N-ethyl-N-isopropyl) amiloride, with a half-maximal inhibitory concentration (IC50) of 1.53 +/- 0.25 mu M. In situ hybridization of rat brain sections revealed significant NHE5 mRNA levels in the dentate gyrus with lower levels observed in the hippocampus and cerebral cortex. These results suggest a specialized role for this fifth NHE isoform in neuronal tissues.