Purchase this article with an account.
Hagen Thieme, Michael Nuskovski, Jens Uwe Nass, Uwe Pleyer, Olaf Strauss, Michael Wiederholt; Mediation of Calcium-Independent Contraction in Trabecular Meshwork through Protein Kinase C and Rho-A. Invest. Ophthalmol. Vis. Sci. 2000;41(13):4240-4246.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
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
acid tetrakis/acetoxymethhyl ester (BAPTA-AM) followed by stimulation
of PKC with phorbolester (PMA) or 4α-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
4α-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 PDF is available to Subscribers Only