Author(s): Thieme H, Nuskovski M, Nass JU, Pleyer U, Strauss O,
Abstract Share this page
Abstract PURPOSE: Inhibition of protein kinase C (PKC) and rho-kinase (ROCK) may represent a new way of influencing outflow facility through isolated relaxation of the trabecular meshwork (TM). This work was performed to investigate the existence of calcium-independent contraction in this smooth-muscle-like tissue and its modulation by targeting the rho-guanosine triphosphatase (GTPase)-mediated pathway. METHODS: Isometric tension measurements of bovine TM and ciliary muscle (CM) were performed. Intra- and extracellular calcium buffering was accomplished with EGTA and 1, 2-bis(2-aminophenoxy)-ethane-N,N:,N:,N:',N:'-tetra-acetic acid tetrakis/acetoxymethhyl ester (BAPTA-AM) followed by stimulation of PKC with phorbolester (PMA) or 4alpha-phorbol. Calcium-independent contraction was blocked using the highly specific ROCK inhibitor Y-27632. Western blot analysis and immunoprecipitation was performed using human TM cells. RESULTS: In TM, carbachol induced partial contraction under conditions of extracellular calcium depletion (22. 1\% +/- 2.3\% versus 100\%, n = 9). The membrane-permeable calcium chelator BAPTA-AM completely blocked this response (1.1\% +/- 1.4\% versus 100\%, n = 9). When calcium was completely blocked, PMA induced contraction in TM (16.7\% +/- 5.9\% versus 100\%, n = 9) but not in CM (1.8\% +/- 2.5\% versus 100\%, n = 6). The inactive PMA analogue 4alpha-phorbol did not induce contraction, indicating that activation of PKC is involved in this contractile response. The ROCK inhibitor Y-27632 completely blocked the calcium-independent PMA-induced contraction in TM. Western blot analysis and immunoprecipitation revealed the expression of the rho-A protein in human TM cells. CONCLUSIONS: The data indicate that contrary to CM, the TM features calcium-independent contractile mechanisms linked to rho-A and PKC isoforms that do not require calcium for activation. ROCK inhibitors may allow specific modulation of the TM to enhance outflow facility, thus lowering intraocular pressure.
This article was published in Invest Ophthalmol Vis Sci
and referenced in Pharmaceutica Analytica Acta