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Lama A. Al-Aswad, Haiyan Gong, David Lee, Martha E. O’Donnell, James D. Brandt, William J. Ryan, Alison Schroeder, Kristine A. Erickson; Effects of Na-K-2Cl Cotransport Regulators on Outflow Facility in Calf and Human Eyes In Vitro. Invest. Ophthalmol. Vis. Sci. 1999;40(8):1695-1701.
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purpose. Cultured human trabecular meshwork (TM) cells possess substantial
Na-K-Cl activity, which is involved in the regulation of TM cell
volume. The hypothesis in the present study was that drugs that affect
the cotransporter might alter aqueous humor outflow facility (C) in the
intact eye. The effects of agents and conditions known to modulate
Na-K-Cl cotransport activity and/or TM cell volume on C in perfused
anterior segments were investigated.
methods. Human and calf eyes were dissected and perfused, and C was determined
according to standard published methods. Perfusates with modified
osmolarity were used to cause alterations in TM cell volume. Cl-free
perfusate and/or bumetanide (10−5 M) was used to inhibit
Na-K-Cl cotransport activity, and vasopressin (10−7 M,
10−8 M) was used to stimulate cotransport activity.
results. In human eyes, hypo-osmotic perfusate decreased C 12%, whereas
hyper-osmotic perfusate increased C 44%. These changes lasted
approximately 30 minutes, after which C began to normalize. Inhibition
of Na-K-Cl cotransport using Cl-free medium or bumetanide resulted in
facility increases of 27% and 22%, respectively. There was an
additive increase in C with bumetanide plus Cl-free media. Stimulating
Na-K-Cl cotransport with 10−8 M and 10−7 M
vasopressin resulted in 28% and 35% decreases in C, respectively. The
results were similar in calf eyes: Cl-free medium or bumetanide
resulted in 41% and 52% increases in C, whereas 10−8 M
and 10−7 M vasopressin resulted in 14% and 19% decreases
in C, respectively.
conclusions. Modulation of Na-K-Cl cotransport results in changes in C that may be
mediated in part by cell volume changes.
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