Reduced water permeability and altered ultrastructure in thin descending limb of Henle in aquaporin-1 null mice
Chung-Lin Chou, … , Tonghui Ma, A.S. Verkman
Chung-Lin Chou, … , Tonghui Ma, A.S. Verkman
Published February 15, 1999
Citation Information: J Clin Invest. 1999;103(4):491-496. https://doi.org/10.1172/JCI5704.
View: Text | PDF
Article

Reduced water permeability and altered ultrastructure in thin descending limb of Henle in aquaporin-1 null mice

Abstract

It has been controversial whether high water permeability in the thin descending limb of Henle (TDLH) is required for formation of a concentrated urine by the kidney. Freeze-fracture electron microscopy (FFEM) of rat TDLH has shown an exceptionally high density of intramembrane particles (IMPs), which were proposed to consist of tetramers of aquaporin-1 (AQP1) water channels. In this study, transepithelial osmotic water permeability (Pf) was measured in isolated perfused segments (0.5–1 mm) of TDLH in wild-type (+/+), AQP1 heterozygous (+/–), and AQP1 null (–/–) mice. Pf was measured at 37°C using a 100 mM bath-to-lumen osmotic gradient of raffinose, and fluorescein isothiocyanate (FITC)–dextran as the luminal volume marker. Pf was (in cm/s): 0.26 ± 0.02 ([+/+]; SE, n = 9 tubules), 0.21 ± 0.01 ([+/–]; n = 12), and 0.031 ± 0.007 ([–/–]; n = 6) (P < 0.02, [+/+] vs. [+/–]; P < 0.0001, [+/+] vs. [–/–]). FFEM of kidney medulla showed remarkably fewer IMPs in TDLH from (–/–) vs. (+/+) and (+/–) mice. IMP densities were (in μm–2, SD, 5–12 micrographs): 5,880 ± 238 (+/+); 5,780 ± 450 (+/–); and 877 ± 420 (–/–). IMP size distribution analysis revealed mean IMP diameters of 8.4 nm ([+/+] and [+/–]) and 5.2 nm ([–/–]). These results demonstrate that AQP1 is the principal water channel in TDLH and support the view that osmotic equilibration along TDLH by water transport plays a key role in the renal countercurrent concentrating mechanism. The similar Pf and AQP1 expression in TDLH of (+/+) and (+/–) mice was an unexpected finding that probably accounts for the unimpaired urinary concentrating ability in (+/–) mice.

Authors

Chung-Lin Chou, Mark A. Knepper, Alfred N. van Hoek, Dennis Brown, Baoxue Yang, Tonghui Ma, A.S. Verkman

×

Figure 1

Options: View larger image (or click on image) Download as PowerPoint
AQP1 expression in kidneys of (+/+), (+/–), and (–/–) mice. (a) Immunope...
AQP1 expression in kidneys of (+/+), (+/–), and (–/–) mice. (a) Immunoperoxidase localization of AQP1 protein in renal cortex and medulla for mice of indicated genotype. Scale bar, 40 μm. (b) Left: Representative immunoblot analysis of renal cortex from mice of indicated genotype. A series of dilutions of samples from (+/+) mice are included as indicated. Right: AQP1 protein expression in renal cortex and medulla (SE, n = 4 mice in each group) determined by quantitative densitometry using standards. (+/+), wild-type mice; (+/–), AQP1 heterozygous mice; (–/–), AQP1 null mice; AQP1, aquaporin-1.