Effect of coupling on volume-regulatory response of ciliary epithelial cells suggests mechanism for secretion

Abstract

The ciliary epithelium of the eye secretes the aqueous humor. It is a double epithelium arranged so that the apical surfaces of the nonpigmented ciliary epithelial (NPCE) and pigmented ciliary epithelial (PCE) cells face each other and the basolateral membranes face the inside of the eye and the blood, respectively. We have investigated the volume responses of both single cells and coupled pairs from this tissue to osmotic challenge. Both NPCE and PCE cells undergo regulatory volume increase (RVI) and decrease (RVD) when exposed to hyper- and hyposmotic solution, respectively. In hyposmotic solution single cells swell and return to their original volumes within ∼3 min. In nonpigmented cells RVD could be inhibited by blockers of volume-activated Cl−channels [tamoxifen (100%) > quinidine (87%) > DIDS (84%) > 5-nitro-2-(3-phenylpropylamino)benzoic acid (80%) > SITS (58%)] and K+ channels [Ba2+(31%)]. However, in PCE cells these inhibitors and additionally tetraethylammonium and Gd3+ were without effect. Only bumetanide, an inhibitor of Na+-K+-2Cl−cotransport, was found to have any effect on RVD in PCE cells. NPCE-PCE cell coupled pairs also underwent RVD, but with altered kinetics. The onset of RVD of the PCE cell in a pair occurred ≈80 s before that of the NPCE cell, and the peak swell was reduced. This is consistent with fluid movement from the PCE to the NPCE cell. The effect of the volume-activated Cl− channel inhibitor tamoxifen was to eliminate this difference in the times of onset of RVD in coupled cell pairs and to inhibit RVD in both the NPCE and PCE cells partially. On the basis of these observations we suggest that fluid is transferred from the PCE to the NPCE cell in coupled pairs during cell swelling and the subsequent RVD. Furthermore, we speculate that reciprocal RVI-RVD could underlie aqueous humor secretion.

Involvement of regulatory volume decrease in the migration of nasopharyngeal carcinoma cells

“…Cell volume and RVD rate were measured using the methods described by us previously [13,14]. Cell suspension of control cells was obtained by trypsinizing cultured cells in a flask and resuspending them in culture medium.…”

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

“…Cell images were captured by a charge-coupled device digital camera (Mono CCD625, Leica, Germany) that was connected to the microscope (Leitz DMIL; Leica Mikroskopie und Systeme, Germany) with a method reported previously (34). The acquisition of the cell images was controlled by the Quantimet Q500MC image processor and analysis software (Leica).…”

Connexin43 is required for production of the aqueous humor in the murine eye

“…Third, NaCl is actively secreted into the aqueous humor by basolateral Na + /K + ATPase and Cl -channels (Civan and Macknight, 2004). Water following this NaCl movement can also pass from PE to NPE via gap junctions (Walker et al, 1999), and exit the NPE to the posterior chamber using basolaterally located aquaporin4 (Yamaguchi et al, 2006). The secretion of NaCl into the posterior chamber may be partially regulated by purinergic A3 receptors since knockout of A3ARs reduces mouse intraocular pressure (IOP) (Avila et al, 2002).…”