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Basolateral AQP2 in the Rat Renal Connecting Tubule (CNT) and Cortical Collecting Duct (CCD) Exhibits Sex Differences

In most principal cells (PC) along the mammalian collecting duct, AQP2 is located in the apical membrane and intracellular recycling vesicles. Recent data by Coleman et al. (AJP 279:F874, 2000) showed that AQP2 may also be present basolaterally in PC of the rat renal CNT/CCD. The importance of this finding for (patho)physiology of water transport in the respective parts of the nephron is unclear. In order to define possible mechanisms of regulation and expression of the basolateral AQP2 in PC of the CNT/CCD, we performed immunofluorescence and immunogold labeling studies in cryosections of the kidney cortex from adult male (M) and female (F) rats. By immunocytochemistry, the AQP2 staining in PC of the CNT/CCD exhibited the following characteristics: a) in both sexes it was present in the apical and the basolateral domain, b) the basolateral staining colocalized with AQP3 and AQP4, and c) the intensity of basolateral staining in F was stronger than in M. As measured by a computer-guided imaging system (IP LabSpectrum, Scanalytics, VA, USA), the intensity of AQP2 staining at the PC apical domain was (average pixel intensity/cell membrane domain, +/-SEM) 1113+/-61 (n=6) and 1373+/-103 (n=6, N.S.) in M and F rats, respectively. The respective data for the basolateral cell domain were 372+/-36 (n=6) and 617+/-33 (n=6) (P<0.001). The total fluorescence (No. of pixels) per cell (1.14 (+/-0.18) x 106 (n=6) in M and 1.54 (+/-0.08) x 106 (n=6) in F, N.S.), as well as the total cell area in mm2 (115+/-7 (n=6) in M and 119+/-5 (n=6) in F, N.S.) were similar in PC cells in both sexes. The localization of AQP2 in the apical and basolateral membrane in PC of the CNT/CCD in both sexes, and the higher abundance of basolateral AQP2 in F, were confirmed by immungold labeling studies. We conclude that: a) AQP2 is constitutively present in both apical and basolateral membrane in PC of the CNT/CCD in rat, and b) the expression of basolateral AQP2 exhibits sex differences (female>male).

gender differences; immunocytochemistry; kidney; nephron; water channels

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