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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 on intracellular hydrostatic pressure of increasing the number of gap junction channels coupling the MFs. (A) The standing hydrostatic pressure gradient in lenses from Cx46 KI 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 12 lenses from six 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. Based on previous studies, the MF coupling conductance in the Cx46 KI lenses is approximately double that in WT lenses (Mathias et al., 2010). Based on the derivation of Eq. 7, if fluid flow in WT and KI lenses is the same, the pressure gradient in the KI lenses should be approximately half that in WT lenses. The best fits of the model to the data give the ratio of pi(0) in Cx46 KI/WT lenses as 0.57. (B) An over-plot of the Cx46 KI and WT data.
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fig4: The effect on intracellular hydrostatic pressure of increasing the number of gap junction channels coupling the MFs. (A) The standing hydrostatic pressure gradient in lenses from Cx46 KI 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 12 lenses from six 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. Based on previous studies, the MF coupling conductance in the Cx46 KI lenses is approximately double that in WT lenses (Mathias et al., 2010). Based on the derivation of Eq. 7, if fluid flow in WT and KI lenses is the same, the pressure gradient in the KI lenses should be approximately half that in WT lenses. The best fits of the model to the data give the ratio of pi(0) in Cx46 KI/WT lenses as 0.57. (B) An over-plot of the Cx46 KI and WT data.

Mentions: When Cx46 was knocked into the Cx50 gene locus (Cx50(46/46)), GMF essentially doubled (Martinez-Wittinghan et al., 2004), and the number of Cx46 channels appeared to double (White, 2002). Thus, we expected that the pressure gradient should be about half that in WT lenses. Pooled pressure measurements from 12 Cx46 KI lenses are graphed as a function of distance from the lens center in Fig. 4 A. Fig. 4 B shows an over-plot of the KI and WT pressure data. As can be seen, the pressure is significantly lower at all radial locations in the KI lenses. Based on the best fit of Eq. 7 to the data, the value of pi(0) was 188 mmHg (see Table I), or a little greater than half that in WT lenses (see Table II). These data are consistent with water flow through an increased number of lens gap junction channels.


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 on intracellular hydrostatic pressure of increasing the number of gap junction channels coupling the MFs. (A) The standing hydrostatic pressure gradient in lenses from Cx46 KI 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 12 lenses from six 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. Based on previous studies, the MF coupling conductance in the Cx46 KI lenses is approximately double that in WT lenses (Mathias et al., 2010). Based on the derivation of Eq. 7, if fluid flow in WT and KI lenses is the same, the pressure gradient in the KI lenses should be approximately half that in WT lenses. The best fits of the model to the data give the ratio of pi(0) in Cx46 KI/WT lenses as 0.57. (B) An over-plot of the Cx46 KI and WT data.
© Copyright Policy - openaccess
Related In: Results  -  Collection

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

fig4: The effect on intracellular hydrostatic pressure of increasing the number of gap junction channels coupling the MFs. (A) The standing hydrostatic pressure gradient in lenses from Cx46 KI 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 12 lenses from six 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. Based on previous studies, the MF coupling conductance in the Cx46 KI lenses is approximately double that in WT lenses (Mathias et al., 2010). Based on the derivation of Eq. 7, if fluid flow in WT and KI lenses is the same, the pressure gradient in the KI lenses should be approximately half that in WT lenses. The best fits of the model to the data give the ratio of pi(0) in Cx46 KI/WT lenses as 0.57. (B) An over-plot of the Cx46 KI and WT data.
Mentions: When Cx46 was knocked into the Cx50 gene locus (Cx50(46/46)), GMF essentially doubled (Martinez-Wittinghan et al., 2004), and the number of Cx46 channels appeared to double (White, 2002). Thus, we expected that the pressure gradient should be about half that in WT lenses. Pooled pressure measurements from 12 Cx46 KI lenses are graphed as a function of distance from the lens center in Fig. 4 A. Fig. 4 B shows an over-plot of the KI and WT pressure data. As can be seen, the pressure is significantly lower at all radial locations in the KI lenses. Based on the best fit of Eq. 7 to the data, the value of pi(0) was 188 mmHg (see Table I), or a little greater than half that in WT lenses (see Table II). These data are consistent with water flow through an increased number of lens gap junction channels.

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