Three different Cl‐ channels in the bovine ciliary epithelium activated by hypotonic stress.

Abstract

1. Hypotonic solution induced transient Cl-channel activity in both pigmented and nonpigmented ciliary epithelial cells in cell-attached patches. 2. The activation time constants for these currents were 63 and 97 s for non-pigmented and pigmented ciliary epithelial (NPCE and PCE) cells, respectively. The currents inactivated during the exposure to hypotonic solution with time constants of 59 and 304 s for NPCE and PCE cells, respectively. 3. Single channel analysis revealed the presence of a low-conductance Cl-channel in both the NPCE (7 3 + 0 4 pS) and PCE (8-6 + 0 9 pS) cells. In addition, an intermediate-conductance (18-8 pS) channel was found alone in the NPCE cells and a maxi Cl-channel (105 pS) was found in the PCE cells. The similarities between the 18-8 pS Cl-channel and the volumeactivated organic osmolyte-anion channel (VSOAC) are discussed. 4. The hypotonic activation of all three Cl-channels was prevented by the inclusion of 100 ,UM 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB) in the patch pipette. 5. Inclusion of tamoxifen in the patch pipette inhibited only the intermediate-conductance channel in the NPCE cells. This is consistent with the identification of the intermediate 18 pS Cl-channel, found only in NPCE cells, as VSOAC. 6. Negative pressure also evoked single Cl-channel activity but the activation kinetics were quite different, suggesting that, even if the channels are the same, the second messenger pathways involved are different. 7. The activation/inactivation kinetics of these Cl-channels correlate well with the time course of regulatory volume decrease (RVD) in these cells, suggesting that these channels may well participate in the process of RVD. 8. The asymmetrical distribution of Cl-channels in the ciliary epithelium may be significant for aqueous humour secretion. For instance, the presence of the VSOAC-like channel in the NPCE cells may allow one-way traffic of anions and organic osmolytes into the eye and, if these solutes were loaded by the PCE cells, then a vectorial flow from the blood into the eye would occur.

Differential volume regulation and calcium signaling in two ciliary body cell types is subserved by TRPV4 channels

“…Excitation mapping showed that TRPV4-induced cation influx takes place in the NPE layer but is absent from the PE layer. This is consistent with critical importance of calcium homeostasis and volume regulation in these aqueous fluid-producing cells (2,4,5,32,33,37,(41)(42)(43)(44). The confinement of the agmatine signal to the vicinity of the plasma membrane suggests that potent local cation clearance mechanisms (Na/K ATPases and PMCAs) limit the diffusion of Ca 2+ signals and their spread across the NPE-PE syncytium.…”

“…It is therefore noteworthy that NPE and PE layers differ in volume sensing, regulation, and the expression and function of volumeactivated Cl − channels, K + channels, PMCAs, Na/K ATPases, and NKCC transporters (5,33,43,44). The distinctiveness of volume regulatory and Ca 2+ homeostatic apparati is consistent with the strikingly different functions in generation and secretion of aqueous humor (2,4 -dependent activity of Na/K ATPases, the primary determinant of aqueous humor secretion (2,5,32,39).…”

The maxi-anion channel: a classical channel playing novel roles through an unidentified molecular entity

“…These channels were similar to those observed in cultured cortical astrocytes from rats [4,49,50] and mice [5][6][7]51] as well as in a rat astrocytic RGCN cell line [52]. In epithelia, the urinary bladder [53], gastric [54], pancreatic [55][56][57], colonic [58][59][60], airway [61][62][63], choroid plexus [64], bile duct [65,66], ciliary [67][68][69], renal [9,19,[70][71][72][73][74][75][76][77][78], vestibular [79], placental [80][81][82][83][84][85][86], ruminal [87] and ovarian [84] epithelial cells were also found to express the maxianion channel with properties similar to those of excitable cells. Resembling maxi-anion channels were also found in fibroblasts [14,…”

Cell cycle-dependent expression of volume-activated chloride currents in nasopharyngeal carcinoma cells

“…It has been reported that there were three types of volume-activated Cl Ϫ channels in ciliary epithelial cells and that the expression of these channels was different between the two cell types of the ciliary epithelium (40). Antisense knockdown of MDR1 (35), ClC-3 (36), or pICln (4) gene expression inhibited the volume-activated Cl Ϫ currents.…”