CHROMOSOMAL ASSIGNMENT OF 4 GENES ENCODING NA/H EXCHANGER ISOFORMS IN HUMAN AND RAT

The plasma membrane Na/H exchanger plays an essential role in regulating intracellular pH and Na+ concentration and has been implicated in several pathophysiological conditions, including essential hypertension and congenital secretory diarrhea. Four isoforms of the Na/H exchanger encoded by separate genes have recently been identified by cDNA cloning. To map their locations in the human and rat genomes, rat isoform-specific cDNA probes were hybridized to Southern filters containing panels of somatic cell hybrids that segregate either human or rat chromosomes. The rat Nhe1 gene was assigned to Chromosome (Chr) 5, extending the homology with human chromosome Ip that has previously been shown to contain the human NHE1 gene. The genes encoding the NHE-2 and NHE-4 isoforms were syntenic in the two species and assigned to rat Chr 9 and human Chr 2. A single Nhe3 gene was detected in rat and assigned to Chr 1. In contrast, although evidence to date has suggested a single human NHE3 gene on Chr 5, two NHE3 genes, NHE3A and NHE3B, were identified and assigned to Chrs 10 and 5, respectively. Interestingly, rat Chr 1 has recently been found to carry a gene controlling systolic blood pressure upon sodium loading in stroke-prone, spontaneously hypertensive rats. Thus, this and other evidence implicates rat Nhe3 as a possible candidate gene in this disease process.