Cloning, sequencing, and expression of Na(+)-H+ antiporter cDNAs from human tissues.

Two types of Na(+)-H+ antiporter with different sensitivities to amiloride analogues have been identified in mammalian plasma membranes. A human Na(+)-H+ antiporter cDNA was obtained by Sardet and co-workers (C. Sardet, L. Counillon, A. Franchi, and J. Pouysségur. Cell 56: 271-280, 1989) using mutant mouse fibroblasts lacking Na(+)-H+ antiporter transformed with human genomic DNA. However, the amiloride sensitivity of this cloned Na(+)-H+ antiporter was not precisely determined. Furthermore, the reported cDNA sequence may be a chimera of human and mouse genes. Hence we isolated a Na(+)-H+ antiporter cDNA actually expressed in human tissues and characterized its amiloride sensitivity. Our 4 kb cDNA obtained from human kidney cortex contained the identical open reading frame to that previously reported and the entire 3' terminus, which was quite different from that reported. This discrepancy was not due to differences in tissue-specific expression because cDNAs from different human tissues were identical, and single bands were observed under high stringency on Northern blots of various human tissues. Na(+)-H+ antiporter activity of mutant mouse fibroblasts deficient in Na(+)-H+ antiporter activity transfected with the cloned cDNA was very sensitive to amiloride and 5-N substituted analogues of amiloride. Thus the cloned cDNA represents the NHE-1 isoform of the Na(+)-H+ antiporter.