Na+-independent anion exchangers (AE) are a family of membrane carriers that mediate the electroneutral exchange of Cl- for HCO3- ions across plasma membranes. They are involved in intracellular pH and cell volume regulation as well as in transepithelial acid-base transport. While anion exchanger-1 (AE1) has been localized previously in the human kidney, thus far there has been no definite report on anion exchanger-2 (AE2) in this human tissue. Accordingly, immunohistochemistry was carried out on surgical specimens of the human kidney (fixed in formalin and embedded in paraffin), using a specific AE2 monoclonal antibody. Strong immunostaining was observed at the basolateral membrane of cells of thick ascending limbs and distal convoluted tubules, colocalizing with the basal membranous labyrinth of cellular interdigitations, typical of these segments. In fact, AE2 staining was attenuated at the macula densa, where basal infoldings are scarce. Additionally, in situ hybridization experiments on formalin-fixed tissue demonstrated the presence of AE2 mRNA in the same segments of the distal nephron. On the other hand, control immunohistochemistry with a monoclonal antibody against AE1 gave the expected immunoreactivity at the basal pole of the type A intercalated cells of connecting tubules and cortical collecting ducts, and in erythrocytes. Our results indicate that, depending on the nephron segment and corresponding cell types, AE1 and AE2 proteins are differentially involved in the Na+-independent exchange of Cl- for HCO3- at the basolateral membrane of polarized kidney epithelial cells.
The use of polymers for the delivery of drugs has increased dramatically in the last decade. To ensure the desired properties and functionality of such substances, adequate characterization in terms of the molar mass (M) and size is essential. The aim of this study was to evaluate the changes in the M and size of PVP-b-PAMPS when the amounts of the synthesis reactants in the two-step radical reaction were varied. The determination of the M and size distributions was performed by an asymmetric flow field-flow fractionation (AF4) system connected to multiangle light scattering (MALS) and differential refractive index (dRI) detectors. The results show that the M of the polymers varies depending on the relative amounts of the reactants and that AF4-MALS-dRI is a powerful characterization technique for analyzing polymers. Using AF4, it was possible to separate the product of the first radical reaction (PVP-CTA) into two populations. The first population had an elongated, rod-like or random coil conformation, and the second had a conformation corresponding to homogeneous spheres or a microgel structure. PVP-b-PAMPS had only one population, which had a rod-like conformation. The molar masses of PVP-CTA and PVP-b-PAMPS found in this study were higher than those reported in previous studies.
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