Molecular basis of altered contractility in experimental colitis: expression of L-type calcium channel

Colitis in experimental animals or idiopathic inflammatory bowel disease, such as ulcerative colitis or Crohn's disease in humans, is associated with reduced muscle contraction. This is predicted to be due to disturbance of Ca2+ homeostasis in the inflamed muscle cell. However, the underlying molecular mechanism remains to be elucidated. Since the catalytic alpha-1 subunit of the L-type Ca2+ channel regulates Ca2+ influx, levels of the alpha-1 mRNA and protein were examined. Colitis induced by intrarectal administration of trinitrobenzenesulfonic acid was monitored by measuring the myeloperoxidase activity and histology. The levels of mRNA and protein were estimated using RT-PCR and immunoblotting. Myeloperoxidase activity increased in the inflamed colon, and the lamina propria and muscle layers showed infiltration of inflammatory cells and loss of crypts. Two alternatively spliced alpha-1 mRNA isoforms were detected in the colonic muscle. The ratio of unspliced to spliced mRNA isoforms remained unaltered in inflamed muscle. In contrast, the level of corresponding protein isozymes decreased in the colitic animals. Thus colitis-induced reduction in the alpha-1 protein may account for the reduced colonic contractility seen in colitis.