Extracellular matrix of the human ciliary muscle

The ciliary muscle forms a major portion of the uveoscleral aqueous outflow pathway. To gain a better understanding of the extracellular matrix of the human ciliary muscle, human ciliary muscle cell cultures at various stages of confluency were immunocytochemically compared with sections of normal ciliary muscle for the presence of collagen types I, III, and IV, fibronectin, and laminin. A pre-embedding immunostaining protocol was employed to obtain good antigen conservation and histologically well-preserved tissue. In subconfluent cultured ciliary muscle cells, collagen types I, III, and IV, fibronectin, and laminin were found intracellularly in the endoplasmic reticulum or in granules surrounding the nucleus. In confluent cells, these matrix molecules each formed characteristic extracellular networks. In normal ciliary muscle, collagen type IV, fibronectin, and laminin were found in the basement membranes around the muscle fibers and blood vessels. Collagen types I and III and fibronectin were observed in the connective tissue among the muscle bundles. Collagen type I also formed a dense band of staining around blood vessels. The biosynthesis and turnover of these glycoproteins may have important roles both in the function of the nonconventional outflow pathway and in mediating the action of certain pharmacological agents.