Immunocytochemical and Phylogenetic Analyses of an Arginine Vasotocin-Dependent Aquaporin, AQP-h2K, Specifically Expressed in the Kidney of the Tree Frog, Hyla japonica

Water movement occurs across the plasma membrane of various cells of animals, plants, and microorganisms through specialized water-channel proteins called aquaporins (AQPs). We have identified a new member of the amphibian AQP family, AQP-h2K, from the kidneys of Hyla japonica. This protein consists of 280 amino acid residues with two NPA (Asn-Pro-Ala) sequence motifs and a mercury-sensitive cysteine residue just upstream from the second NPA motif. There are two putative N-linked glycosylation sites at Asn-120 and Asn-128 and one protein kinase A phosphorylation site at Ser-262. The AQP-h2K protein was specifically expressed in the apical membrane and/or cytoplasm of principal cells in the kidney collecting ducts. After stimulation with arginine vasotocin, it was translocated from the cytoplasmic pool to the apical membrane. Phylogenetic analysis of AQP proteins from anurans and mammals identified six clusters of anuran AQPs: types 1, 2, 3, and 5 and two anuran-specific types, designated a1 and a2. The cl...