CALPONIN DISTRIBUTION IN HUMAN CILIARY MUSCLE AND OTHER ANTERIOR SEGMENT TISSUES

Purpose. Calponins are a family of actin-binding proteins known to reg ulate aortic and tracheal smooth muscle contraction. This investigatio n was undertaken to assess the presence, subtype, and distribution of calponin proteins in human ciliary muscle, iris, and other anterior se gment tissues as well as expression in ciliary muscle cells in vitro. Methods. The distribution of calponin immunoreactivity was assessed in paraffin sections of human anterior segment tissue. Human ciliary mus cle proteins were analyzed by polyacrylamide gel electrophoresis and W estern blotting. The regulation of calponin expression was compared wi th alpha-sm-actin expression in preconfluent and postconfluent ciliary muscle cell cultures by immunocytochemistry. To determine total cell counts, the cultures were counterstained with ethidium homodimer. As c ontrol specimens; expression of calponin and alpha-sm-actin also was a ssessed in human Tenon fibroblast cultures. Results. Strong calponin i mmunoreactivity was present in ciliary muscle, iris dilator and sphinc ter muscles, and blood vessel smooth muscle. Fine immunostained strand s also were observed in the scleral spur. This distribution was simila r to alpha-sm-actin. Western blotting showed a single band of calponin with a molecular weight of 32 kDa. In the cultured ciliary muscle cel ls, calponin stained straight cable-like fibers running parallel along the long axis of the cells. Although the proportion of calponin immun oreactive cells was reduced substantially in preconfluent cultures, vi rtually all cells were stained in confluent primary through fourth-pas sage cultures. Cultured human Tenon fibroblasts did not show either ca lponin or alpha-sm-actin immunoreactivity. Conclusions. Calponin is ex pressed in human ciliary muscle, iris smooth muscles, blood vessel smo oth muscle, as well as within the scleral spur. In addition, calponin is expressed by ciliary smooth muscle cells in vitro. The role of calp onin in contraction of these tissues should be investigated.