Immunocytochemical localization of smooth muscle actin-containing cells in the trabecular meshwork of glaucomatous and nonglaucomatous dogs.

ABSTRACT

PURPOSE: It has been recently demonstrated that trabecular meshwork (TM) cells within the canine iridocorneal angle (ICA) contain smooth muscle actin (smA) and possess contractile abilities that probably alter aqueous outflow. As the number of trabecular meshwork cells in glaucomatous canine eyes have been found to be less than those in age-matched nonglaucomatous eyes, we hypothesize that the sub-population of TM cells that contain smooth muscle actin will also decline with age. We also hypothesize that a greater loss of these cells will be observed in glaucomatous eyes than in nonglaucomatous eyes of the same age. In the present study the ICA of 17 glaucomatous and eight nonglaucomatous eyes were examined for the presence of smA-containing TM cells. MATERIAL AND METHODS: Five-micron sagittal sections of each whole globe were immunolocalized for smooth muscle actin. Positive and negative controls were performed concomitantly. RESULTS: Labeling was observed in the meshwork of 10 out of the 17 glaucomatous eyes, distributed across all of the age groups represented, including eyes with primary and secondary glaucoma. Smooth muscle actin labeling was observed in the TM of 7 out of 14 eyes with closed-angle glaucoma. Positive immunoreaction was observed in 3/3 eyes with open ICAs. Labeling of smooth muscle actin was observed in the anterior part of the meshwork in only 4 of the 17 glaucomatous eyes, each having had secondary glaucoma. There were no eyes in which label was observed exclusively in the anterior portion of the meshwork. Labeling was most consistently observed in the outer, posterior uveal TM and the inner, posterior corneoscleral TM. All of the eight nonglaucomatous eyes showed greater labeling in both area and intensity than the glaucomatous eyes of the same age. CONCLUSION: It was concluded that smooth muscle actin-cell loss is associated with age in canine eyes and that this loss is more severe in glaucomatous eyes.