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Departments of 1 Human Physiology and 2 Neurology, School of Medicine, University of California, Davis, California 95616
The cDNA
encoding the
Na+/H+
exchanger (NHE) from Amphiuma
erythrocytes was cloned, sequenced, and found to be highly homologous to the human NHE1 isoform (hNHE1), with 79% identity and 89%
similarity at the amino acid level. Sequence comparisons with other
NHEs indicate that the Amphiuma
tridactylum NHE isoform 1 (atNHE1) is
likely to be a phylogenetic progenitor of mammalian NHE1. The atNHE1
protein, when stably transfected into the NHE-deficient AP-1 cell line
(37), demonstrates robust
Na+-dependent proton transport
that is sensitive to amiloride but not to the potent NHE1 inhibitor
HOE-694. Interestingly, chimeric NHE proteins constructed by exchanging
the amino and carboxy termini between atNHE1 and hNHE1 exhibited drug
sensitivities similar to atNHE1. Based on kinetic, sequence, and
functional similarities between atNHE1 and mammalian NHE1, we propose
that the Amphiuma exchanger should
prove to be a valuable model for studying the control of pH and volume
regulation of mammalian NHE1. However, low sensitivity of atNHE1 to the
NHE inhibitor HOE-694 in both native
Amphiuma red blood cells (RBCs) and in
transfected mammalian cells distinguishes this transporter from its
mammalian homologue.
sodium/proton antiport; amiloride; HOE-694; intracellular pH; red blood cells
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