Identification of the protein and cDNA of the cardiac Na+ /H+ exchanger

We examined the myocardial form of the Na+ /H+ exchanger. A partial length cDNA clone was isolated from a rabbit cardiac library and it encoded for a Na+ /H+ exchange protein. In comparison with the human Na+ /H+ exchanger, the sequence of the 5′ end of the cDNA was highly conserved, much more than the 3/t' region, while the deduced amino acid sequence was also highly conserved. To further characterize the myocardial Na+ /H+ exchange protein, we examined Western blots of isolated sarcolemma with antibody produced against a fusion protein of the Na+ /H+ exchanger. The antibodies reacted with a sarcolemma protein of 50 kDa and with a protein of 70 kDa. The results show that the rabbit myocardium does possess a Na+ /H+ exchanger protein homologous to the known human Na+ /H+ exchanger.