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P.J. Donaldson, K.N. Chee, K.F. Webb, J. Kistler; Spatially Distinct Cl– Influx and Efflux Pathways Interact to Maintain Lens Volume and Transparency . Invest. Ophthalmol. Vis. Sci. 2005;46(13):1129.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To investigate the relative contributions of Cl– channels and transporters to a circulating flux of chloride ions which has been implicated in the control of lens volume and transparency. Methods: Organ cultured rat lenses and isolated fiber cells were exposed to various Cl– transport inhibitors under either isotonic or hypotonic conditions. In whole lenses the effects of inhibitors on cellular morphology were determined by confocal microscopy. In isolated fiber cells the effects of inhibitors and osmolarity on membrane conductance and cell volume were monitored by whole cell patch clamping and video microscopy, respectively. Results: The incubation of lenses in the presence of the KCl cotransporter inhibitor, DIOA, produced peripheral cell swelling, while the addition of the Cl– channel inhibitor, NPPB, caused extracellular space dilations between deeper fiber cells. These results suggest that the influx and efflux pathways for Cl– are different, spatially separated and change during the course of fiber cell differentiation. Consistent with this view, fiber cells isolated from different areas of the lens cortex exhibited differences in Cl– conductance, and the ability to undergo a regulatory volume decrease (RVD). Under isotonic conditions short peripheral fiber cells (<50µm) tended to have a minimal Cl– conductance, but upon exposure to a hyposmotic solution were capable of a RVD that was inhibited by DIOA. Interestingly, exposure of short fiber cells to hyposmotic solutions plus DIOA caused cell swelling and the subsequent activation of a Cl– conductance. In contrast longer fiber cells (>120µm) were dominated by an outwardly rectifying Cl– conductance which was blocked by NPPB. Conclusions: In young peripheral fiber cells Cl– efflux is mediated by KCl cotransporters, while in older deeper fiber cells Cl– influx occurs via a conductive pathway. Since fiber cells are connected by gap junction channels it is expected that the spatially distinct Cl– influx and efflux pathways will produce a circulating flux of Cl– ions. This implies that the maintenance of lens cell volume and transparency is critically dependant on the interplay between anion channels and transporters.
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