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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Bottom Line: Aqueous fluid volume and [Cl(-)] were assayed in samples withdrawn by micropipettes.However, AQP deletion did not significantly affect outflow, [Cl(-)], volume, or compliance.AQP inhibition may thus provide a novel approach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 Aqueous fluid volume and [Cl(-)] were assayed in samples withdrawn by micropipettes.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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Aqueous fluid outflow by the continuous infusion method. (A) Representative experiment showing IOP recording in response to continuous fluid infusion. Fluid was infused continuously into the anterior chamber by a micropipette to obtain constant specified IOP. Infusion was transiently increased to >10 μl/h to increase IOP, followed by empirical changes by in 0.5-μl/h steps to keep IOP constant. (inset) Magnified view for setting IOP to ∼25 mmHg. (B) Aqueous fluid outflow versus Δ(IOP) (IOP − IOPo) determined from experiments as in A. Mean ± SE, n = 8 eyes.
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fig2: Aqueous fluid outflow by the continuous infusion method. (A) Representative experiment showing IOP recording in response to continuous fluid infusion. Fluid was infused continuously into the anterior chamber by a micropipette to obtain constant specified IOP. Infusion was transiently increased to >10 μl/h to increase IOP, followed by empirical changes by in 0.5-μl/h steps to keep IOP constant. (inset) Magnified view for setting IOP to ∼25 mmHg. (B) Aqueous fluid outflow versus Δ(IOP) (IOP − IOPo) determined from experiments as in A. Mean ± SE, n = 8 eyes.

Mentions: Two independent methods were used to measure aqueous fluid outflow: a continuous infusion method and a pulsed infusion method; the latter method also provided information about the compliance of the aqueous fluid compartment. In the continuous infusion method, as reported for measurements in rat eye (Mermoud et al., 1996), IOP was monitored during continuous perfusion of fluid into the aqueous compartment. The rate of fluid infusion was determined empirically (see Fig. 2 A) to maintain constant IOP at a series of predetermined levels. In the pulsed infusion method, 0.1 μl infusions (rate, 20 ml/min) of fluid were made every minute during continuous IOP recording (see Fig. 3 A). From these data, volume vs. pressure (V vs. IOP) and outflow vs. pressure (dV/dt vs. IOP) curves were constructed for each eye studied (and later averaged for mice of the same genotype and genetic background) as follows: for each 0.1 μl fluid infusion, the initial and final IOPs were tabulated along with the slope [d(IOP)/dt]. Aqueous fluid volume was computed at each IOP from the measured volume at physiological IOP (see below) and the summed incremental volumes resulting from the fluid additions (after correction for outflow). The resultant V vs. IOP relation defines the compliance of the aqueous fluid compartment. Aqueous fluid outflow was computed from d(IOP)/dt and compliance: dV/dt = dV/d(IOP) · d(IOP)/dt. Since measured outflow at physiological IOP (IOPo) is zero as determined by the continuous and pulsed infusion methods, the measured outflow is less than total outflow at each IOP by a quantity equal to the inflow at physiological IOP. We therefore report outflow as dV/dt vs. Δ(IOP), where Δ(IOP) = IOP − IOPo.


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

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

Aqueous fluid outflow by the continuous infusion method. (A) Representative experiment showing IOP recording in response to continuous fluid infusion. Fluid was infused continuously into the anterior chamber by a micropipette to obtain constant specified IOP. Infusion was transiently increased to >10 μl/h to increase IOP, followed by empirical changes by in 0.5-μl/h steps to keep IOP constant. (inset) Magnified view for setting IOP to ∼25 mmHg. (B) Aqueous fluid outflow versus Δ(IOP) (IOP − IOPo) determined from experiments as in A. Mean ± SE, n = 8 eyes.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2233864&req=5

fig2: Aqueous fluid outflow by the continuous infusion method. (A) Representative experiment showing IOP recording in response to continuous fluid infusion. Fluid was infused continuously into the anterior chamber by a micropipette to obtain constant specified IOP. Infusion was transiently increased to >10 μl/h to increase IOP, followed by empirical changes by in 0.5-μl/h steps to keep IOP constant. (inset) Magnified view for setting IOP to ∼25 mmHg. (B) Aqueous fluid outflow versus Δ(IOP) (IOP − IOPo) determined from experiments as in A. Mean ± SE, n = 8 eyes.
Mentions: Two independent methods were used to measure aqueous fluid outflow: a continuous infusion method and a pulsed infusion method; the latter method also provided information about the compliance of the aqueous fluid compartment. In the continuous infusion method, as reported for measurements in rat eye (Mermoud et al., 1996), IOP was monitored during continuous perfusion of fluid into the aqueous compartment. The rate of fluid infusion was determined empirically (see Fig. 2 A) to maintain constant IOP at a series of predetermined levels. In the pulsed infusion method, 0.1 μl infusions (rate, 20 ml/min) of fluid were made every minute during continuous IOP recording (see Fig. 3 A). From these data, volume vs. pressure (V vs. IOP) and outflow vs. pressure (dV/dt vs. IOP) curves were constructed for each eye studied (and later averaged for mice of the same genotype and genetic background) as follows: for each 0.1 μl fluid infusion, the initial and final IOPs were tabulated along with the slope [d(IOP)/dt]. Aqueous fluid volume was computed at each IOP from the measured volume at physiological IOP (see below) and the summed incremental volumes resulting from the fluid additions (after correction for outflow). The resultant V vs. IOP relation defines the compliance of the aqueous fluid compartment. Aqueous fluid outflow was computed from d(IOP)/dt and compliance: dV/dt = dV/d(IOP) · d(IOP)/dt. Since measured outflow at physiological IOP (IOPo) is zero as determined by the continuous and pulsed infusion methods, the measured outflow is less than total outflow at each IOP by a quantity equal to the inflow at physiological IOP. We therefore report outflow as dV/dt vs. Δ(IOP), where Δ(IOP) = IOP − IOPo.

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