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Aquaporin deletion in mice reduces intraocular pressure and aqueous fluid production.

Zhang D, Vetrivel L, Verkman AS - J. Gen. Physiol. (2002)

Bottom Line: Aqueous fluid volume and [Cl(-)] were assayed in samples withdrawn by micropipettes.However, AQP deletion did not significantly affect outflow, [Cl(-)], volume, or compliance.AQP inhibition may thus provide a novel approach for the treatment of elevated IOP.

View Article: PubMed Central - PubMed

Affiliation: Department of Medicine and Physiology, Cardiovascular Research Institute, 1246 Health Sciences East Tower, University of California at San Francisco, San Francisco, CA 94143, USA.

ABSTRACT
Aquaporin (AQP) water channels are expressed in the eye at sites of aqueous fluid production and outflow: AQP1 and AQP4 in nonpigmented ciliary epithelium, and AQP1 in trabecular meshwork endothelium. Novel methods were developed to compare aqueous fluid dynamics in wild-type mice versus mice lacking AQP1 and/or AQP4. Aqueous fluid production was measured by in vivo confocal microscopy after transcorneal iontophoretic introduction of fluorescein. Intraocular pressure (IOP), outflow, and anterior chamber compliance were determined from pressure measurements in response to fluid infusions using micropipettes. Aqueous fluid volume and [Cl(-)] were assayed in samples withdrawn by micropipettes. In wild-type mice (CD1 genetic background, age 4-6 wk), IOP was 16.0 +/- 0.4 mmHg (SE), aqueous fluid volume 7.2 +/- 0.3 microl, fluid production 3.6 +/- 0.2 microl/h, fluid outflow 0.36 +/- 0.06 microl/h/mmHg, and compliance 0.036 +/- 0.006 microl/mmHg. IOP was significantly decreased by up to 1.8 mmHg (P < 0.002) and fluid production by up to 0.9 microl/h in age/litter-matched mice lacking AQP1 and/or AQP4 (outbred CD1 and inbred C57/bl6 genetic backgrounds). However, AQP deletion did not significantly affect outflow, [Cl(-)], volume, or compliance. These results provide evidence for the involvement of AQPs in intraocular pressure regulation by facilitating aqueous fluid secretion across the ciliary epithelium. AQP inhibition may thus provide a novel approach for the treatment of elevated IOP.

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Intraocular pressure. (A) Schematic of measurement method showing the introduction of a fluid-filled micropipette into the anterior chamber through the cornea. In calibration studies, a second micropipette connected to a fluid-filled manometer was inserted (left, shown in gray). (B) Validation of IOP measurements. Measured IOP shown as a function of pressure set by manometer fluid height. (C) Time course of IOP in wild-type mice. Where indicated mice were given mannitol (20%, 2.5 g/kg), acetazolamide (8 mg/kg), or water (0.1 ml/g, intraperitoneal). (D) IOP measurements in wild-type mice, AQP1 and AQP4  mice, and AQP1/AQP4 double knockout mice showing data in individual eyes (filled circles) and mean ± SE (open circles). *, P < 0.05, **, P < 0.002 (ANOVA).
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fig1: Intraocular pressure. (A) Schematic of measurement method showing the introduction of a fluid-filled micropipette into the anterior chamber through the cornea. In calibration studies, a second micropipette connected to a fluid-filled manometer was inserted (left, shown in gray). (B) Validation of IOP measurements. Measured IOP shown as a function of pressure set by manometer fluid height. (C) Time course of IOP in wild-type mice. Where indicated mice were given mannitol (20%, 2.5 g/kg), acetazolamide (8 mg/kg), or water (0.1 ml/g, intraperitoneal). (D) IOP measurements in wild-type mice, AQP1 and AQP4 mice, and AQP1/AQP4 double knockout mice showing data in individual eyes (filled circles) and mean ± SE (open circles). *, P < 0.05, **, P < 0.002 (ANOVA).

Mentions: Micropipettes were introduced into the mouse cornea using a 4-axis micromanipulator (Narishige) at an angle of 45° from the vertical at a location of ∼0.2 mm from the center of the cornea. Care was taken to avoid contact with the lens surface. Micropipettes were connected using short noncompliant tubing to a pressure transducer (MX860; Medex, Inc.) interfaced to a recording system (model MP100; Biopac). The circuit also permitted fluid introduction using a syringe pump (Harvard Apparatus) driving a gas-tight glass Hamilton syringe. The quality of the tubing and connections was found to be critical for accurate and stable IOP measurements, as well as elimination of small air bubbles. At the completion of each experiment the micropipette tip was withdrawn from the cornea to verify a reading of 0 mmHg. In validation studies, IOP was set at a series of specified levels (3.7–22 mmHg) by introducing a second micropipette into the anterior chamber that was connected to a fluid manometer (see Fig. 1 A).


Aquaporin deletion in mice reduces intraocular pressure and aqueous fluid production.

Zhang D, Vetrivel L, Verkman AS - J. Gen. Physiol. (2002)

Intraocular pressure. (A) Schematic of measurement method showing the introduction of a fluid-filled micropipette into the anterior chamber through the cornea. In calibration studies, a second micropipette connected to a fluid-filled manometer was inserted (left, shown in gray). (B) Validation of IOP measurements. Measured IOP shown as a function of pressure set by manometer fluid height. (C) Time course of IOP in wild-type mice. Where indicated mice were given mannitol (20%, 2.5 g/kg), acetazolamide (8 mg/kg), or water (0.1 ml/g, intraperitoneal). (D) IOP measurements in wild-type mice, AQP1 and AQP4  mice, and AQP1/AQP4 double knockout mice showing data in individual eyes (filled circles) and mean ± SE (open circles). *, P < 0.05, **, P < 0.002 (ANOVA).
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2233864&req=5

fig1: Intraocular pressure. (A) Schematic of measurement method showing the introduction of a fluid-filled micropipette into the anterior chamber through the cornea. In calibration studies, a second micropipette connected to a fluid-filled manometer was inserted (left, shown in gray). (B) Validation of IOP measurements. Measured IOP shown as a function of pressure set by manometer fluid height. (C) Time course of IOP in wild-type mice. Where indicated mice were given mannitol (20%, 2.5 g/kg), acetazolamide (8 mg/kg), or water (0.1 ml/g, intraperitoneal). (D) IOP measurements in wild-type mice, AQP1 and AQP4 mice, and AQP1/AQP4 double knockout mice showing data in individual eyes (filled circles) and mean ± SE (open circles). *, P < 0.05, **, P < 0.002 (ANOVA).
Mentions: Micropipettes were introduced into the mouse cornea using a 4-axis micromanipulator (Narishige) at an angle of 45° from the vertical at a location of ∼0.2 mm from the center of the cornea. Care was taken to avoid contact with the lens surface. Micropipettes were connected using short noncompliant tubing to a pressure transducer (MX860; Medex, Inc.) interfaced to a recording system (model MP100; Biopac). The circuit also permitted fluid introduction using a syringe pump (Harvard Apparatus) driving a gas-tight glass Hamilton syringe. The quality of the tubing and connections was found to be critical for accurate and stable IOP measurements, as well as elimination of small air bubbles. At the completion of each experiment the micropipette tip was withdrawn from the cornea to verify a reading of 0 mmHg. In validation studies, IOP was set at a series of specified levels (3.7–22 mmHg) by introducing a second micropipette into the anterior chamber that was connected to a fluid manometer (see Fig. 1 A).

Bottom Line: Aqueous fluid volume and [Cl(-)] were assayed in samples withdrawn by micropipettes.However, AQP deletion did not significantly affect outflow, [Cl(-)], volume, or compliance.AQP inhibition may thus provide a novel approach for the treatment of elevated IOP.

View Article: PubMed Central - PubMed

Affiliation: Department of Medicine and Physiology, Cardiovascular Research Institute, 1246 Health Sciences East Tower, University of California at San Francisco, San Francisco, CA 94143, USA.

ABSTRACT
Aquaporin (AQP) water channels are expressed in the eye at sites of aqueous fluid production and outflow: AQP1 and AQP4 in nonpigmented ciliary epithelium, and AQP1 in trabecular meshwork endothelium. Novel methods were developed to compare aqueous fluid dynamics in wild-type mice versus mice lacking AQP1 and/or AQP4. Aqueous fluid production was measured by in vivo confocal microscopy after transcorneal iontophoretic introduction of fluorescein. Intraocular pressure (IOP), outflow, and anterior chamber compliance were determined from pressure measurements in response to fluid infusions using micropipettes. Aqueous fluid volume and [Cl(-)] were assayed in samples withdrawn by micropipettes. In wild-type mice (CD1 genetic background, age 4-6 wk), IOP was 16.0 +/- 0.4 mmHg (SE), aqueous fluid volume 7.2 +/- 0.3 microl, fluid production 3.6 +/- 0.2 microl/h, fluid outflow 0.36 +/- 0.06 microl/h/mmHg, and compliance 0.036 +/- 0.006 microl/mmHg. IOP was significantly decreased by up to 1.8 mmHg (P < 0.002) and fluid production by up to 0.9 microl/h in age/litter-matched mice lacking AQP1 and/or AQP4 (outbred CD1 and inbred C57/bl6 genetic backgrounds). However, AQP deletion did not significantly affect outflow, [Cl(-)], volume, or compliance. These results provide evidence for the involvement of AQPs in intraocular pressure regulation by facilitating aqueous fluid secretion across the ciliary epithelium. AQP inhibition may thus provide a novel approach for the treatment of elevated IOP.

Show MeSH
Related in: MedlinePlus