McLean L A, Zia S, Gorin F A, Cala P M
Department of Human Physiology, School of Medicine, University of California, Davis, California 95616, USA.
Am J Physiol. 1999 May;276(5):C1025-37. doi: 10.1152/ajpcell.1999.276.5.C1025.
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.
克隆并测序了来自美洲鳗红细胞的编码钠氢交换体（NHE）的cDNA，发现其与人NHE1亚型（hNHE1）高度同源，在氨基酸水平上具有79%的同一性和89%的相似性。与其他NHE的序列比较表明，三线美洲鳗NHE亚型1（atNHE1）可能是哺乳动物NHE1的系统发育祖先。当atNHE1蛋白稳定转染到缺乏NHE的AP-1细胞系（37）中时，表现出强大的钠依赖性质子转运，对氨氯地平敏感，但对强效NHE1抑制剂HOE-694不敏感。有趣的是，通过交换atNHE1和hNHE1的氨基和羧基末端构建的嵌合NHE蛋白表现出与atNHE1相似的药物敏感性。基于atNHE1和哺乳动物NHE1之间的动力学、序列和功能相似性，我们提出美洲鳗交换体应该被证明是研究哺乳动物NHE1的pH控制和体积调节的有价值模型。然而，atNHE1在天然美洲鳗红细胞（RBC）和转染的哺乳动物细胞中对NHE抑制剂HOE-694的低敏感性使其与哺乳动物同源物区分开来。
