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C.W. Do, K. Peterson–Yantorno, M.M. Civan; Swelling–Activated Cl– Channels Support Cl– SecretionbBy Bovine Ciliary Epithelium . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2903.
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© ARVO (1962-2015); The Authors (2016-present)
To determine if swelling–activated Cl– currents (ICl,swell) observed in isolated nonpigmented ciliary epithelial (NPE) cells contribute to Cl– secretion across ciliary epithelium, and whether the effect is mediated by enhancing NPE–cell fluid release.
Ion transport across intact bovine ciliary epithelium was monitored electrically. Native isolated bovine NPE cells were harvested enzymatically. Cell volume changes were measured by calcein–fluorescence quenching.
Bilateral reduction in osmolality transiently increased short–circuit current (Isc), averaging ∼60–70%. Bilateral pretreatment with NPPB, a Cl– channel blocker, reduced Isc stimulation by ∼60%, suggesting that transcellular ICl,swell largely mediated the increased current. The hypotonic–triggered Isc stimulation was also inhibited by phloretin, a blocker of swelling–activated Cl– channels and by flufenamic acid, a blocker of Cl– and nonselective cation channels. Cyclamate substitution for bath Cl– reduced the baseline Isc and the hypotonically–triggered Isc increase; and in that case, pretreatment of NPPB and flufenamic acid did not produce further inhibition. The transepithelial responses were correlated with regulatory volume responses of harvested NPE cells. Hypotonicity elicited a regulatory volume decrease (RVD) over a time period comparable to that of the hypotonicity–triggered increase in Isc. The RVD was also inhibited by Cl––channel blockers and by Cl– substitution.
ICl,swell of NPE cells is functionally expressed in intact ciliary epithelium and oriented to subserve aqueous humor formation. NPE–cell volume can be measured with calcein–fluorescence quenching. The stimulation of ICl,swell facilitates Cl– secretion, leading to increased fluid release by the NPE cells into the posterior chamber.
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