Na+/H+ exchanger in tissues of lower vertebrates

Na+/H+ exchange is one of the major pathways of ion transport in cells of pro- and eukaryots and plays an important role in intracellular pH and cell volume regulation, in cell division, proliferation, as well as in epithelial transport processes. Since 1989, investigations on the molecular nature of this transporter have revealed six isoforms (NHE1-NHE6) in mammalian tissues. Most works on studies of properties of the Na/H antiporter and regulation of its activity have been carried out on mammalian tissues. This review summarizes results of studies on the Na+/H+ exchange in tissues of lower vertebrates. Of the greatest interest are investigations on the rainbow trout, whose erythrocytes were found to contain a Na+/H+ exchanger activated by catecholamines. This carrier in trout erythrocytes has been cloned and called beta-NHE (betaNHE). Another exchanger isoform, at NHE, was isolated from the red blood cells of the giant salamander Amphiuma tridactulum. Isoforms of antiporter isolated from oocytes (XL-NHE) and renal cells of the clawed frog Xenopus laevis (XNHE) have also been described.