Distribution of gap junction protein connexin 37 in smooth muscle cells of the rat trachea and pulmonary artery.

Connexin 37, one of the gap junction protein families, has been detected by Northern blotting in various organs and tissues, and found to be especially abundant in the lung. However, detailed information on the precise types of cells which express connexin 37 has not been previously published. We therefore prepared site-specific connexin 37 antibodies and examined the distribution of connexin 37 immunohistochemically. Connexin 37 was detected in endothelial cells, in the tunica media of both the pulmonary artery and the aorta, and in the smooth muscle layer of the trachea and bronchioles. In the tracheal smooth muscle layer, connexin 37 overlapped with desmin-positive areas, but was clearly segregated from vimentin- and von Willebrand factor-positive areas. These results suggest that connexin 37 is expressed in smooth muscle cells in the trachea, but not in fibroblastic cells or endothelial cells. Connexin 37 was partially colocalized with connexin 43 in tracheal smooth muscle cells, and showed a gradual increase in expression during postnatal development. To our knowledge, this is the first report to be published regarding the expression of connexin 37 in smooth muscle cells.