Calponin distribution in human ciliary muscle and other anterior segment tissues.
OBJECTIVE
Calponins are a family of actin-binding proteins known to regulate aortic and tracheal smooth muscle contraction. This investigation was undertaken to assess the presence, subtype, and distribution of calponin proteins in human ciliary muscle, iris, and other anterior segment 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 muscle proteins were analyzed by polyacrylamide gel electrophoresis and Western blotting. The regulation of calponin expression was compared with alpha-sm-actin expression in preconfluent and postconfluent ciliary muscle cell cultures by immunocytochemistry. To determine total cell counts, the cultures were counter-stained with ethidium homodimer. As control specimens, expression of calponin and alpha-sm-actin also was assessed in human Tenon fibroblast cultures.


RESULTS
Strong calponin immunoreactivity was present in ciliary muscle, iris dilator and sphincter muscles, and blood vessel smooth muscle. Fine immunostained strands also were observed in the scleral spur. This distribution was similar to alpha-sm-actin. Western blotting showed a single band of calponin with a molecular weight of 32 kDa. In the cultured ciliary muscle cells, calponin stained straight cable-like fibers running parallel along the long axis of the cells. Although the proportion of calponin immunoreactive cells was reduced substantially in preconfluent cultures, virtually all cells were stained in confluent primary through fourth-passage cultures. Cultured human Tenon fibroblasts did not show either calponin or alpha-sm-actin immunoreactivity.


CONCLUSIONS
Calponin is expressed in human ciliary muscle, iris smooth muscles, blood vessel smooth muscle, as well as within the scleral spur. In addition, calponin is expressed by ciliary smooth muscle cells in vitro. The role of calponin in contraction of these tissues should be investigated.
Kashiwagi
K
K
Glaucoma Center, University of California, San Diego, La Jolla 92093, USA.
Lindsey
J D
JD
Kashiwagi
F
F
Tsukahara
S
S
Weinreb
R N
RN
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000869:Anterior Eye Segment / Q000378:metabolism*; D000911:Antibodies, Monoclonal; D015153:Blotting, Western; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D002148:Calmodulin-Binding Proteins / Q000378:metabolism*; D002478:Cells, Cultured; D002924:Ciliary Body / Q000378:metabolism*; D003238:Connective Tissue / Q000378:metabolism; D003239:Connective Tissue Cells; D004591:Electrophoresis, Polyacrylamide Gel; D005347:Fibroblasts / Q000378:metabolism; D019084:Fluorescent Antibody Technique, Indirect; D006801:Humans; D007124:Immunoenzyme Techniques; D008840:Microfilament Proteins / Q000378:metabolism*; D008875:Middle Aged; D009124:Muscle Proteins / Q000378:metabolism*; D009130:Muscle, Smooth / Q000378:metabolism*; D000096985:Calponins
D000911:Antibodies, Monoclonal; D002135:Calcium-Binding Proteins; D002148:Calmodulin-Binding Proteins; D008840:Microfilament Proteins; D009124:Muscle Proteins; D000096985:Calponins