Adrenoceptor-mediated Cl
- transport in cultured rabbit corneal endothelium was examined using a Cl
--sensitive fluorescent dye. The intracellular Cl
- concentration ([Cl
-]
i) in the endothelial cells was estimated to be about 30 mM. Noradrenaline (0.001-0.1 mM) transiently decreased the [Cl
-]
i in a dose-dependent manner. Such a decrease in [Cl
--]
i was completely antagonized by pretreatment with the α-adrenoceptor antagonist phentolamine (0.1 mM). The selective α
2-adrenoceptor agonist UK 14304-18 (5-bromo-6-[(4
H, 5
H-imidazol-2-yl)amino]quinoxaline, 0.1 mM) persistently decreased the [Cl
-]
i, but neither the α
1-adrenoceptor agonist phenylephrine (0.1 mM) nor the β-adrenoceptor agonist isoproterenol (0.1 mM) had any effect. The α
2-adrenoceptor agonist/antagonist yohimbine (0.1 mM) persistently and more strongly decreased the [Cl
-]
i than UK 14304-18 did. The yohimbine-induced decrease in the [Cl
-]
i was not further altered by UK 14304-18 or phenylephrine, but partly reversed by noradrenaline, isoproterenol and an adenylate cyclase activator, forskolin (0.1 mM). The yohimbine-induced decrease in [Cl
-]
i was inhibited by the carbonic anhydrase inhibitor acetazolamide (1 mM), and Cl
--/HC0
3- exchange inhibitors, 4-acetamido-4'' -isothiocyanostilbene-2, 2'' disulfonic acid and 4, 4'' -diisothiocyanostilbene-2, 2''-disulfonic acid, but not by the H
+-ATPase inhibitor
N, N'' dicyclohexylcarbodiimide. The forskolin-induced recovery in [Cl
-]
i was inhibited by the Na
+/K
+/Cl
- cotransport inhibitor bumetanide (0.1 mM), but not by the Cl
-channel blocker 5-nitro-2-(3-phenylpropylamino)-benzoic acid. These findings suggest that corneal endothelial cells extrude Cl
- upon α
2-adrenoceptor stimulation and accumulate Cl
- upon β-adrenoceptor stimulation under low [Cl
-]
i conditions, probably via acceleration of Cl
-/HC0
3- exchange and Na
+/K
+/ Cl
- cotransport, respectively.
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