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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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Related in: MedlinePlus

The standing hydrostatic pressure gradient in lenses from WT mice, which were ∼2 mo old. The hydrostatic pressure (pi mmHg) is graphed as a function of normalized distance (r/a) from the lens center, where a (cm) is the lens radius, and r (cm) is the distance from the lens center. The data are from 14 lenses from seven mice. The pressures at two to six radial locations were recorded from each lens. The smooth curve is the best fit of Eq. 7 to the data.
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fig3: The standing hydrostatic pressure gradient in lenses from WT mice, which were ∼2 mo old. The hydrostatic pressure (pi mmHg) is graphed as a function of normalized distance (r/a) from the lens center, where a (cm) is the lens radius, and r (cm) is the distance from the lens center. The data are from 14 lenses from seven mice. The pressures at two to six radial locations were recorded from each lens. The smooth curve is the best fit of Eq. 7 to the data.

Mentions: Fig. 3 illustrates the hydrostatic pressure gradient measured in WT mouse lenses. The data were recorded in 14 lenses taken from seven mice. The pressures at two to six locations in each lens were recorded, and then the data from all 14 lenses were pooled and graphed as a function of normalized distance from the lens center. The smooth curve is the best fit of Eq. 7 to the pooled data. Table I includes average parameter values for this group of lenses. The best-fit value for the average pressure at the lens center was 328 mmHg. For a lens whose radius is a = 1 mm and fiber cell width is w = 3 µm, there are 333 shells of gap junctions; hence, the average pressure drop across each shell of gap junctions is ∼1 mmHg. The presence of the measured standing hydrostatic pressure gradient shown in Fig. 3 suggests the existence of intracellular fluid flow from the lens center to surface. It also suggests that the fluid flow might be through lens gap junction channels, because a large pressure gradient was predicted in the Theory section for water flow through gap junction channels. Nevertheless, one could think of other possibilities, so we sought more direct evidence on whether gap junction channels were mediating water flow.


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 standing hydrostatic pressure gradient in lenses from WT mice, which were ∼2 mo old. The hydrostatic pressure (pi mmHg) is graphed as a function of normalized distance (r/a) from the lens center, where a (cm) is the lens radius, and r (cm) is the distance from the lens center. The data are from 14 lenses from seven mice. The pressures at two to six radial locations were recorded from each lens. The smooth curve is the best fit of Eq. 7 to the data.
© Copyright Policy - openaccess
Related In: Results  -  Collection

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

fig3: The standing hydrostatic pressure gradient in lenses from WT mice, which were ∼2 mo old. The hydrostatic pressure (pi mmHg) is graphed as a function of normalized distance (r/a) from the lens center, where a (cm) is the lens radius, and r (cm) is the distance from the lens center. The data are from 14 lenses from seven mice. The pressures at two to six radial locations were recorded from each lens. The smooth curve is the best fit of Eq. 7 to the data.
Mentions: Fig. 3 illustrates the hydrostatic pressure gradient measured in WT mouse lenses. The data were recorded in 14 lenses taken from seven mice. The pressures at two to six locations in each lens were recorded, and then the data from all 14 lenses were pooled and graphed as a function of normalized distance from the lens center. The smooth curve is the best fit of Eq. 7 to the pooled data. Table I includes average parameter values for this group of lenses. The best-fit value for the average pressure at the lens center was 328 mmHg. For a lens whose radius is a = 1 mm and fiber cell width is w = 3 µm, there are 333 shells of gap junctions; hence, the average pressure drop across each shell of gap junctions is ∼1 mmHg. The presence of the measured standing hydrostatic pressure gradient shown in Fig. 3 suggests the existence of intracellular fluid flow from the lens center to surface. It also suggests that the fluid flow might be through lens gap junction channels, because a large pressure gradient was predicted in the Theory section for water flow through gap junction channels. Nevertheless, one could think of other possibilities, so we sought more direct evidence on whether gap junction channels were mediating water flow.

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