Volume regulation in the bovine lens and cataract. The involvement of chloride channels.

Abstract

The purpose of this study was to investigate volume regulation in the lens and its involvement in lens opacification (cataract) and the role of chloride channels in these processes. Single, isolated lens fiber cells from the lens were whole cell patch clamped. When exposed to hypotonic solution, an outwardly rectifying whole-cell current was activated. The current increased from 1.0 to 32.6 pA/pF, reversed at the chloride reversal potential (E Cl ϭ 0 mV), and was blocked by the chloride channel blockers 5, nitro-2-(3-phenylpropylamino) benzoate (NPPB) and tamoxifen. Replacing all but 5 mM of the external chloride with gluconate caused the reversal potential to shift ϩ 33 mV, consistent with a Cl Ϫ current with a gluconate/chloride permeability ratio of 0.26. When the whole lens of the eye was exposed to hypotonic solution, there was an initial increase in anteriorposterior diameter (5-8 min), representing lens swelling of 6.5%. This was followed by a decrease in volume to a new steady state value that lasted for up to 2 h. In the longer term ( Ն 2 h), the lenses began to swell again. The simultaneous exposure to hypotonic solution and tamoxifen or NPPB caused swelling and prevented this volume regulation. Lenses incubated in hypotonic solution and hypotonic solution containing tamoxifen became opaque after a 2-h incubation period. We conclude that the lens is able to volume regulate. It possesses volume-activated Cl Ϫ channels, the inhibition of which results in inhibition of volume regulation, lens swelling and opacification. Our data suggest the longterm prophylactic use of tamoxifen may make the patient more susceptible to cataract.

Localised Fibre Cell Swelling Characteristic of Diabetic Cataract Can Be Induced in Normal Rat Lens Using the Chloride Channel Blocker 5-Nitro-2-(3-Phenylpropylamino) Benzoic Acid

“…Over the remaining 18 h of incubation, the mass of lenses in hypotonic AAH gradually decreased, returning to within 20% of their initial mass by the end of the incubation period at 36 h. This decrease in lens mass following hypotonic challenge agrees with the results reported in an earlier study of rat lens [5], and leads to the conclusion that whole lenses are able to regulate their volume under hypotonic conditions. The role of chloride channels in this RVD was investigated by incubating lenses in hypotonic saline for 18 h, and then in hypotonic saline containing NPPB for the remaining 18 h. Compared to lenses maintained continuously in hypotonic AAH alone, the mass of the NPPB-treated lenses remained significantly elevated at 36 h, a finding consistent with a recent study in bovine lens [6]. Hence, chloride channels mediate volume regulation in the osmotically challenged lens.…”

Induction of cortical cataracts in cultured mouse lenses with H-89, an inhibitor of protein kinase A

“…43 This activity is mediated by Pglycoprotein, 44 a multifunctional complex for the transport of chloride, water and organic molecules that is modified by phosphorylation. 45 The relative roles of NKCC, NaKATPase and P-glycoprotein in the development of H-89 cataract deserve further investigation.…”

Expression of pICln mRNA in cultured bovine lens epithelial cells: response to changes in cell volume

“…[9][10][11][12][13]18,28 Moreover, it has recently been demonstrated that tamoxifen influences lens opacification in whole lens studies of bovine eyes. 28,29 In an intact lens study, tamoxifen was reported to increase lens swelling by up to 13% and prevented volume regulation upon a hypotonic insult. 29 Furthermore, niflumic acid has been shown to prolong cell swelling by inhibiting RVD in nonpigmented ciliary epithelial cells.…”

“…28,29 In an intact lens study, tamoxifen was reported to increase lens swelling by up to 13% and prevented volume regulation upon a hypotonic insult. 29 Furthermore, niflumic acid has been shown to prolong cell swelling by inhibiting RVD in nonpigmented ciliary epithelial cells. 18 As shown in Figures 4A and 4B, swelling-activated myo-[ 3 H]inositol efflux is inhibited in a dose-dependent manner by the chloride channel inhibitors tamoxifen and niflumic acid, respectively.…”