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The Trabecular Meshwork Can Contract And Regulate Fluid Outflow

Submitted by dave on Wed, 03/07/2007 - 1:58pm

Michael Wiederholt says, "Research in this laboratory has demonstrated that trabecular meshwork has contractile properties, is actively involved in outflow regulation..." Below is an abstract of one of the studies on this topic he helped author.

The regulation of trabecular meshwork and ciliary muscle contractility

Current models of aqueous humor outflow no longer treat trabecular meshwork (TM) as an inert tissue passively distended by the ciliary muscle (CM). Instead, ample evidence supports the theory that trabecular meshwork possesses smooth muscle-like properties and is actively involved in the regulation of aqueous humor outflow and intraocular pressure. In this model, trabecular meshwork and ciliary muscle appear as functional antagonists, with ciliary muscle contraction leading to a distension of trabecular meshwork with subsequent reduction in outflow, and with trabecular meshwork contraction leading to the opposite effect.

Smooth-muscle relaxing substances would therefore appear to be ideal candidates for glaucoma therapy with the dual goal of reducing intraocular pressure via the trabecular meshwork and of improving vascular perfusion of the optic nerve head. However, for such substances to effectively lower intraocular pressure, the effect on the ciliary muscle would have to be minimal. For this reason, more information is needed on the signalling processes involved in regulating trabecular meshwork and ciliary muscle contractility.

This review attempts to outline current knowledge of signal transduction pathways leading to relaxation and contraction of ciliary muscle and trabecular meshwork. Pathways can be classified as involving or not involving changes of membrane voltage and of requiring or not requiring external calcium; possibly, other pathways exist. These different pathways involve different ion channels and isoforms of PKC and are expressed to a differing degree in ciliary muscle and trabecular meshwork, leading to differential responses when exposed to relaxing or contracting pharmacological agents. Some of these agents, like tyrosine kinase inhibitors and inhibitors of PKC, have been shown to relax trabecular meshwork while leaving ciliary muscle comparatively unaffected. This profile makes these substances appear as ideal drugs for simultaneously improving ocular outflow and retinal circulation, parameters that determine the time course of visual deterioration in glaucoma.

Michael Wiederholt, Hagen Thieme and Friederike Stumpff 

Institut für Klinische Physiologie, Universitätsklinikum Benjamin Franklin, Freie Universität Berlin, 12200 Berlin, Germany 

Progress in Retinal and Eye Research 
Volume 19, Issue 3 , May 2000, Pages 271-295




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