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Lens intracellular hydrostatic pressure is generated by the circulation of sodium and modulated by gap junction coupling.

Gao J, Sun X, Moore LC, White TW, Brink PR, Mathias RT - J. Gen. Physiol. (2011)

Bottom Line: Intracellular hydrostatic pressure in lenses from these mouse models varied inversely with the number of channels.When the lens' circulation of Na(+) was either blocked or reduced, intracellular hydrostatic pressure in central fiber cells was either eliminated or reduced proportionally.These data are consistent with our hypotheses: fluid circulates through the lens; the intracellular leg of fluid circulation is through gap junction channels and is driven by hydrostatic pressure; and the fluid flow is generated by membrane transport of sodium.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Physiology and Biophysics, SUNY at Stony Brook, NY 11794, USA.

ABSTRACT
We recently modeled fluid flow through gap junction channels coupling the pigmented and nonpigmented layers of the ciliary body. The model suggested the channels could transport the secretion of aqueous humor, but flow would be driven by hydrostatic pressure rather than osmosis. The pressure required to drive fluid through a single layer of gap junctions might be just a few mmHg and difficult to measure. In the lens, however, there is a circulation of Na(+) that may be coupled to intracellular fluid flow. Based on this hypothesis, the fluid would cross hundreds of layers of gap junctions, and this might require a large hydrostatic gradient. Therefore, we measured hydrostatic pressure as a function of distance from the center of the lens using an intracellular microelectrode-based pressure-sensing system. In wild-type mouse lenses, intracellular pressure varied from ∼330 mmHg at the center to zero at the surface. We have several knockout/knock-in mouse models with differing levels of expression of gap junction channels coupling lens fiber cells. Intracellular hydrostatic pressure in lenses from these mouse models varied inversely with the number of channels. When the lens' circulation of Na(+) was either blocked or reduced, intracellular hydrostatic pressure in central fiber cells was either eliminated or reduced proportionally. These data are consistent with our hypotheses: fluid circulates through the lens; the intracellular leg of fluid circulation is through gap junction channels and is driven by hydrostatic pressure; and the fluid flow is generated by membrane transport of sodium.

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The effect of Na/K ATPase inhibition with a saturating concentration of ouabain on central intracellular pressure in WT lenses. (A) Typical data from one lens showing the time course of the reduction in central hydrostatic pressure after blockade of the Na/K ATPase. After ∼30 min in ouabain, pressure near the center of the lens dropped to about half its original value. (B) The average time course of reduction in hydrostatic pressure in six lenses from six mice. The time course represents several events with different time scales, as described in Results.
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fig8: The effect of Na/K ATPase inhibition with a saturating concentration of ouabain on central intracellular pressure in WT lenses. (A) Typical data from one lens showing the time course of the reduction in central hydrostatic pressure after blockade of the Na/K ATPase. After ∼30 min in ouabain, pressure near the center of the lens dropped to about half its original value. (B) The average time course of reduction in hydrostatic pressure in six lenses from six mice. The time course represents several events with different time scales, as described in Results.

Mentions: Fig. 8 A shows the effect of a saturating concentration of ouabain on the central hydrostatic pressure in a typical lens. Fig. 8 B shows the averaged normalized central pressure from six lenses after immersion in normal Tyrode’s solution containing a saturating concentration of ouabain. The pressure declined to 50% of its initial value in a period of ∼30 min. Thus, as expected, the effect of ouabain is more rapid but not as complete as that of high K+/low Na+ solution. We assume that solute circulation declined to 50% normal in the first 15 min (Parmelee, 1986), and then it required another 15 min for sufficient water to be transported out of the lens for the central pressure to drop to 50% normal. Once the intracellular concentration gradient for Na+ has been dissipated, there will be slow accumulation of global Na+ as it enters fiber cells but is not transported out of the epithelial cells. Similarly, K+ will deplete to maintain electroneutrality as it moves out of epithelial cells and is replaced by Na+ (see Fig. 1 B). As a result, the fiber cell transmembrane electrochemical gradient for Na+ slowly moves toward equilibrium (0 mV). We observed intracellular pressures for a total of 100 min. In the last 70 min, one can see the slow linear decline in pressure that probably reflects this slow equilibration.


Lens intracellular hydrostatic pressure is generated by the circulation of sodium and modulated by gap junction coupling.

Gao J, Sun X, Moore LC, White TW, Brink PR, Mathias RT - J. Gen. Physiol. (2011)

The effect of Na/K ATPase inhibition with a saturating concentration of ouabain on central intracellular pressure in WT lenses. (A) Typical data from one lens showing the time course of the reduction in central hydrostatic pressure after blockade of the Na/K ATPase. After ∼30 min in ouabain, pressure near the center of the lens dropped to about half its original value. (B) The average time course of reduction in hydrostatic pressure in six lenses from six mice. The time course represents several events with different time scales, as described in Results.
© Copyright Policy - openaccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC3105514&req=5

fig8: The effect of Na/K ATPase inhibition with a saturating concentration of ouabain on central intracellular pressure in WT lenses. (A) Typical data from one lens showing the time course of the reduction in central hydrostatic pressure after blockade of the Na/K ATPase. After ∼30 min in ouabain, pressure near the center of the lens dropped to about half its original value. (B) The average time course of reduction in hydrostatic pressure in six lenses from six mice. The time course represents several events with different time scales, as described in Results.
Mentions: Fig. 8 A shows the effect of a saturating concentration of ouabain on the central hydrostatic pressure in a typical lens. Fig. 8 B shows the averaged normalized central pressure from six lenses after immersion in normal Tyrode’s solution containing a saturating concentration of ouabain. The pressure declined to 50% of its initial value in a period of ∼30 min. Thus, as expected, the effect of ouabain is more rapid but not as complete as that of high K+/low Na+ solution. We assume that solute circulation declined to 50% normal in the first 15 min (Parmelee, 1986), and then it required another 15 min for sufficient water to be transported out of the lens for the central pressure to drop to 50% normal. Once the intracellular concentration gradient for Na+ has been dissipated, there will be slow accumulation of global Na+ as it enters fiber cells but is not transported out of the epithelial cells. Similarly, K+ will deplete to maintain electroneutrality as it moves out of epithelial cells and is replaced by Na+ (see Fig. 1 B). As a result, the fiber cell transmembrane electrochemical gradient for Na+ slowly moves toward equilibrium (0 mV). We observed intracellular pressures for a total of 100 min. In the last 70 min, one can see the slow linear decline in pressure that probably reflects this slow equilibration.

Bottom Line: Intracellular hydrostatic pressure in lenses from these mouse models varied inversely with the number of channels.When the lens' circulation of Na(+) was either blocked or reduced, intracellular hydrostatic pressure in central fiber cells was either eliminated or reduced proportionally.These data are consistent with our hypotheses: fluid circulates through the lens; the intracellular leg of fluid circulation is through gap junction channels and is driven by hydrostatic pressure; and the fluid flow is generated by membrane transport of sodium.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Physiology and Biophysics, SUNY at Stony Brook, NY 11794, USA.

ABSTRACT
We recently modeled fluid flow through gap junction channels coupling the pigmented and nonpigmented layers of the ciliary body. The model suggested the channels could transport the secretion of aqueous humor, but flow would be driven by hydrostatic pressure rather than osmosis. The pressure required to drive fluid through a single layer of gap junctions might be just a few mmHg and difficult to measure. In the lens, however, there is a circulation of Na(+) that may be coupled to intracellular fluid flow. Based on this hypothesis, the fluid would cross hundreds of layers of gap junctions, and this might require a large hydrostatic gradient. Therefore, we measured hydrostatic pressure as a function of distance from the center of the lens using an intracellular microelectrode-based pressure-sensing system. In wild-type mouse lenses, intracellular pressure varied from ∼330 mmHg at the center to zero at the surface. We have several knockout/knock-in mouse models with differing levels of expression of gap junction channels coupling lens fiber cells. Intracellular hydrostatic pressure in lenses from these mouse models varied inversely with the number of channels. When the lens' circulation of Na(+) was either blocked or reduced, intracellular hydrostatic pressure in central fiber cells was either eliminated or reduced proportionally. These data are consistent with our hypotheses: fluid circulates through the lens; the intracellular leg of fluid circulation is through gap junction channels and is driven by hydrostatic pressure; and the fluid flow is generated by membrane transport of sodium.

Show MeSH
Related in: MedlinePlus