Human trabecular meshwork cell volume regulation

• Published in: American Journal of Physiology: Cell Physiology Vol. 283; no. 1; pp. C315 - C326
• Main Authors: Mitchell, Claire H, Fleischhauer, Johannes C, Stamer, W. Daniel, Peterson-Yantorno, K, Civan, Mortimer M
• Format: Journal Article
• Language: English
• Published: United States 01.07.2002
• Subjects: Bicarbonates - pharmacology; Calcium - metabolism; Cell Line; Chlorides - pharmacology; Humans; Intracellular Membranes - metabolism; Ion Transport - physiology; K Cl- Cotransporters; Mesylates - pharmacology; Models, Biological; Patch-Clamp Techniques; Sodium-Hydrogen Exchangers - physiology; Symporters - physiology; Trabecular Meshwork - cytology; Trabecular Meshwork - drug effects; Trabecular Meshwork - metabolism; Trabecular Meshwork - physiology
• ISSN: 0363-6143; 1522-1563
• DOI: 10.1152/ajpcell.00544.2001

Departments of 1  Physiology and 2  Medicine, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-6085; and 3  Department of Ophthalmology, University of Arizona, Tucson, Arizona 85711-1824 The volume of certain subpopulations of trabecular meshwork (TM) cells may modify outflow resistance of aqueous humor, thereby altering intraocular pressure. This study examines the contribution that Na + /H + , Cl /HCO exchange, and K + -Cl efflux mechanisms have on the volume of TM cells. Volume, Cl currents, and intracellular Ca 2+ activity of cultured human TM cells were studied with calcein fluorescence, whole cell patch clamping, and fura 2 fluorescence, respectively. At physiological bicarbonate concentration, the selective Na + /H + antiport inhibitor dimethylamiloride reduced isotonic cell volume. Hypotonicity triggered a regulatory volume decrease (RVD), which could be inhibited by the Cl channel blocker 5-nitro-2-(3-phenylpropylamino)-benzoate (NPPB), the K + channel blockers Ba 2+ and tetraethylammonium, and the K + -Cl symport blocker [(dihydroindenyl)oxy]alkanoic acid. The fluid uptake mechanism in isotonic conditions was dependent on bicarbonate; at physiological levels, the Na + /H + exchange inhibitor dimethylamiloride reduced cell volume, whereas at low levels the Na + -K + -2Cl symport inhibitor bumetanide had the predominant effect. Patch-clamp measurements showed that hypotonicity activated an outwardly rectifying, NPPB-sensitive Cl channel displaying the permeability ranking Cl  > methylsulfonate > aspartate. 2,3-Butanedione 2-monoxime antagonized actomyosin activity and both increased baseline [Ca 2+ ] and abolished swelling-activated increase in [Ca 2+ ], but it did not affect RVD. Results indicate that human TM cells display a Ca 2+ -independent RVD and that volume is regulated by swelling-activated K + and Cl channels, Na + /H + antiports, and possibly K + -Cl symports in addition to Na + -K + -2Cl symports. outflow facility; calcein; chloride channels; potassium-chloride symport; sodium/hydrogen antiport; methylsulfonate; aspartate; intraocular pressure; [(dihydroindenyl)oxy]alkanoic acid