X Liu1, N J Rusch, J Striessnig, S K Sarna. 1. Department of Surgery, Medical College of Wisconsin and Zablocki VA Medical Center, Milwaukee, Wisconsin, USA.
Abstract
BACKGROUND & AIMS: Circular smooth muscle phasic contractions and tone are suppressed during colonic inflammation, but the contributing factors are poorly understood. This study investigated if the expression level of voltage-gated long-lasting (L-type) Ca(2+) channel protein and functional Ca(2+) channel current are down-regulated in the circular muscle cells of the inflamed canine colon. METHODS: L-type Ca(2+) channel expression was compared between normal and inflamed smooth muscle cells by Western immunoblots using an antibody directed against the pore-forming alpha 1C-subunit, and patch-clamp methods were used to evaluate Ca(2+) channel current density. RESULTS: The expression of the L-type Ca(2+) channel protein was significantly reduced in inflamed compared with normal circular smooth muscle cell membranes, and this finding was associated with suppressed levels of Ca(2+) channel current in patch-clamped cells. The L-type Ca(2+) channel current in normal and inflamed cells increased proportionately in response to Bay K 8644, but the maximal current density was still lower in the inflamed cells. Acetylcholine increased the L-type Ca(2+) channel current in normal but not in inflamed cells. CONCLUSIONS: The expression level of L-type Ca(2+) channels is down-regulated in the circular smooth muscle cell membranes of the inflamed colon, which may result in reduced Ca(2+) influx. The functional and pharmacologic properties of the channels seem normal. Although some Ca(2+) channels are still present in the inflamed cells, acetylcholine does not activate these channels, which may be caused by additional upstream defects in the receptor signaling cascade. The down-regulation of L-type Ca(2+) channel expression may suppress circular smooth muscle contractions in the inflamed colon and contribute to the abnormalities in motility and digestion observed during inflammatory disorders.
BACKGROUND & AIMS: Circular smooth muscle phasic contractions and tone are suppressed during colonic inflammation, but the contributing factors are poorly understood. This study investigated if the expression level of voltage-gated long-lasting (L-type) Ca(2+) channel protein and functional Ca(2+) channel current are down-regulated in the circular muscle cells of the inflamed canine colon. METHODS: L-type Ca(2+) channel expression was compared between normal and inflamed smooth muscle cells by Western immunoblots using an antibody directed against the pore-forming alpha 1C-subunit, and patch-clamp methods were used to evaluate Ca(2+) channel current density. RESULTS: The expression of the L-type Ca(2+) channel protein was significantly reduced in inflamed compared with normal circular smooth muscle cell membranes, and this finding was associated with suppressed levels of Ca(2+) channel current in patch-clamped cells. The L-type Ca(2+) channel current in normal and inflamed cells increased proportionately in response to Bay K 8644, but the maximal current density was still lower in the inflamed cells. Acetylcholine increased the L-type Ca(2+) channel current in normal but not in inflamed cells. CONCLUSIONS: The expression level of L-type Ca(2+) channels is down-regulated in the circular smooth muscle cell membranes of the inflamed colon, which may result in reduced Ca(2+) influx. The functional and pharmacologic properties of the channels seem normal. Although some Ca(2+) channels are still present in the inflamed cells, acetylcholine does not activate these channels, which may be caused by additional upstream defects in the receptor signaling cascade. The down-regulation of L-type Ca(2+) channel expression may suppress circular smooth muscle contractions in the inflamed colon and contribute to the abnormalities in motility and digestion observed during inflammatory disorders.
Authors: Dinesh K Hirenallur-S; Steven T Haworth; Jeaninne T Leming; James Chang; Guillermo Hernandez; John B Gordon; Nancy J Rusch Journal: Am J Physiol Lung Cell Mol Physiol Date: 2008-09-05 Impact factor: 5.464