Abstract. The variant chicken kidney AE1 anion exchangers differ only at the NH 2 terminus of their cytoplasmic domains. Transfection studies have indicated that the variant chicken AE1-4 anion exchanger accumulates in the basolateral membrane of polarized MDCK kidney epithelial cells, while the AE1-3 variant, which lacks the NH 2-terminal 63 amino acids of AE1-4, primarily accumulates in the apical membrane. Mutagenesis studies have shown that the basolateral accumulation of AE1-4 is dependent upon two tyrosine residues at amino acids 44 and 47 of the polypeptide. Interestingly, either of these tyrosines is sufficient to direct efficient basolateral sorting of AE1-4. However, in the absence of both tyrosine residues, AE1-4 accumulates in the apical membrane of MDCK cells. Pulse– chase studies have shown that after delivery to the cell surface, newly synthesized AE1-4 is recycled to the THE kidney plays an essential role in the regulation of pH equilibrium within the body. This regulatory function is accomplished by the wide variety of transporters and channels that mediate the vectorial transport of ions within the cells of the kidney. This selective transport of ions requires the presence of different complements of polypeptides in the apical and basolateral membrane domains of the polarized epithelial cells of the kidney. Although cytoplasmic (Casanova et al., 1991; Matte
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