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Vol. 273, Issue 5, C1480-C1486, November 1997
cotransport
Eye Research Institute, Oakland University, Rochester, Michigan 48309-4401
The role of
Na+-K+-2Cl
cotransport in ion and fluid transport of the corneal endothelium was
examined by measuring changes in corneal hydration and uptake of
86Rb by the endothelial cell
layer. Isolated, intact rabbit corneas maintain normal hydration when
they are superfused at the endothelial surface with bicarbonate
(
)-Ringer solutions as a
result of equilibrium between active ion and fluid transport out of the
stromal tissue and leak of fluid into stromal tissue from the aqueous
humor. Furosemide and bumetanide did not alter this equilibrium when
they were added to the superfusion medium. Uptake of
86Rb by the endothelium of the
incubated cornea was increased 25% by bumetanide, but uptake in the
presence of ouabain (70% less than that of controls) was not changed
by bumetanide. In Na+-free medium,
uptake of 86Rb was reduced by
58%, but it was unchanged in
Cl-free medium. Calyculin
A, a protein phosphatase inhibitor and activator of
Na+-K+-Cl
cotransport, was without effect on
86Rb uptake. Hypertonicity (345 mosmol/kg) increased uptake slightly, whereas hypotonicity (226 mosmol/kg) caused a 33% decrease. Neither of these changes was
significantly different when bumetanide was present in the media. It is
concluded that
Na+-K+-2Cl
cotransporter activity is not exhibited by the in situ corneal endothelium and does not play a role in the ion and fluid transport of
this cell layer. Its presence in cultured endothelial cells may reflect
the reported importance of this protein in growth, proliferation, and
differentiation.
sodium; potassium; chloride; bumetanide; rubidium-86 uptake; corneal hydration; calyculin A; hypertonicity
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