3D finite element model of aqueous outflow to predict the effect of femtosecond laser created partial thickness drainage channels

Background and Objectives Partial thickness drainage channels can be created with femtosecond lasers in the translucent sclera for the potential treatment of glaucoma. We present a 3D finite element model (FEM) that can predict the effect of these channels on aqueous humor (AH) outflow and intraocular pressure (IOP). Study Design/Materials and Methods A 3D model was developed based on a 2D model for the intact eye using COMSOL (Comsol, Inc., MA) finite element software. Different values of permeability were entered into the 3D model for the AH pathway and for the partial thickness channel. To obtain experimental data for model validation, one partial thickness channel was created in each of three enucleated rabbit eyes with a femtosecond laser tuned to 1.7 µm wavelength. Aqueous outflow rates were measured with the perfusion method before and after the laser treatments at different levels of IOP and then compared to IOP values predicted by the model. Results The experiments indicated that the rate of the AH outflow was increased in each of three eyes after the laser treatment. Assuming a constant rate of AH production the 3D model predicted IOP reductions ranging from 67.2% to 80.6% as the effect of the laser created channels. These predictions were in reasonable agreement with experimentally adjusted IOP values during the perfusion measurements. Conclusions The developed 3D FEM has the potential to predict IOP reduction caused by partial thickness drainage channels created with the femtosecond laser in the sclera. Such a model may also be used to determine optimal channel dimensions for a specified increase in outflow facility and reduction in IOP. Laser Surg. Med. 40:188–195, 2008. © 2008 Wiley-Liss, Inc.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/58067/1/20608_ftp.pd

Glutathione S-transferases in the organ of Corti of the rat: Enzymatic activity, subunit composition and immunohistochemical localization

Glutathione S-transferases (GSTs), a family of ubiquitous cytosolic isozymes, catalyze the detoxification of electrophilic substrates with reduced glutathione and participate in intracellular binding and transport of lipophilic substances. This study measured GST activity biochemically in the inner ear of the rat; determined the isozyme profile by Western blotting; and identified, immunohistochemically. the distribution of the [mu] and [pi] class GSTs in the organ of Corti. GST enzymatic activity in inner ear tissues ranged from 117 to 348 nmoles glutathione converted/min/mg protein, values somewhat higher than those found in brain (130) and much lower than in liver (1011). Of the GST isoforms, the [pi] class (identified by antibodies against the Yp subunit) was most prominent, the [mu] class (Yb1 subunit) clearly evident while the [alpha] class (Ya subunit) was barely detectable on Western blots. Immunocytochemical analysis showed differential distribution of the Yh1 and Yp subunits. The Yb1 subunit was present in the sensory cells, while supporting cells were not specifically stained. At the subcellular level, the isozyme was localized in the apical zones of inner (IHCs) and outer hair cells (OHCs) close to the cuticular plate. The extent of staining, however, varied between OHCs and IHCs. In the OHCs, staining appeared in discrete spots in the apical areas only, whereas in IHCs staining extended further towards the center of the cells. The Yp subunit was mainly localized to Deiters cell processes and pillar cells. Both Yb1 and Yp colocalized with tubulin-specific antibody.The functional significance of GST in the cochlear receptor cells is speculative. However, a role anologous to that in other tissues (detoxification, prostaglandin synthesis) can be assumed. In addition, an association of GST with the microtubule system is possible based on immunohistochemical colocalization with tubulin.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30402/1/0000022.pd

Membrane voltage recordings in a cell line derived from human ciliary muscle

A smooth muscle cell line (H7CM) was established from the ciliary muscle of a 1-day-old human infant. The cultured cells had a normal female karyotype (46 XX) and could be maintained in cell culture for at least 11 generations. A common feature of confluent cultures was the presence of abundant bundles of 6-7 nm microfilaments associated with dense bodies. Both the ultrastructural appearance and the presence of smooth muscle-specific alpha-isoactin (also present in the human ciliary muscle in situ) support the smooth muscle origin of the H7CM cell line. Continuous membrane voltage (Vm) recordings were obtained in confluent monolayers of H7CM cells using glass microelectrodes. Resting Vm in 105 impalements averaged -66.2 +/- 0.7 mV (mean +/- standard error of the mean). In this system, rapid membrane transients induced by changing of the superfusing test solutions were detectable. Relative K+ conductance was characterized, and the contribution of electrogenic sodium/potassium adenosine triphosphatase to Vm was investigated. Under control conditions, H7CM cells were electrically quiescent. However, action potentials could be induced by application of 10 mM barium. Barium-induced action potentials were not abolished by removal of extracellular Na+ nor were they inhibited by the presence of tetrodotoxin. However, they were blocked by verapamil, fulfilling criteria believed to be typical for smooth muscle cells. Acetylcholine, carbachol, and to a lesser extent pilocarpine induced a reversible Vm depolarization. The effect of acetylcholine was blocked by atropine, implying muscarinic receptor involvement in the Vm response. Collectively, these findings show the potential usefulness of cultured ciliary muscle cells in understanding further the cellular mechanisms underlying drug-induced contraction of the human ciliary muscle

Effect of Endofhelin on Outflow Facility and Accommodation in the Monkey Eye In Vivo

The effect of the vasoactive peptide, endothelin, on facility -of outflow, accommodation, and pupil diameter was measured in the monkey eye in vivo. Endothelin increased the outflow facility 22-71% at approximate anterior chamber concentrations ranging from 10~1 0 -10~7 M. Endothelin-induced accommodation was modest but consistent and statistically significant ranging from 1.61 to a maximum of 2.43 diopters at 10~9 M and 10~7 M endothelin, respectively. No change in pupil diameter was noted with any of the administered doses. These data demonstrate an action of endothelin on outflow facility and, together with prior evidence indicating the presence of endothelin receptors on the ciliary muscle, suggest that, like cholinergic agonists, the observed effects of endothelin on outflow facility may be mediated, at least in part, through an action on the ciliary muscle. Invest Ophthalmol Vis Sci 32: [492][493][494][495]1991 Endothelins are a group of vasoconstrictor polypeptides which have recently been isolated from porcine aortic endothelial cells. 1 Effects of endothelin on the cardiovascular system are similar to those of angiotensin II, but endothelin is much more potent. Endothelin also contracts nonvascular smooth muscle. " 4 A recent report documented that endothelin causes a membrane voltage depolarization and an increase in intracellular calcium in cultured human ciliary muscle cells at a concentration about two orders of magnitude lower than acetylcholine. 5 This result points to a possible physiologic role for endothelin in the ciliary muscle. In this report, we describe the results of in vivo experiments that demonstrate endothelin-mediated effects on both the facility of outflow and accommodation. Materials and Methods Five female cynomolgus monkeys (Macaca fascicularis) whose weights ranged from 2-3 kg were used in this study. For each procedure, the monkey was From th