Impaired activation of cytosolic phospolipase A(2) in inflamed canine colonic circular muscle

Transcriptional regulation of inflammatory mediators secreted by human colonic circular smooth muscle cells

We investigated the transcriptional regulation of secretion of pro- and anti-inflammatory mediators by human colonic circular smooth muscle cells (HCCSMC) in response to tumor necrosis factor (TNF)-alpha. Gene chip array analysis indicated that HCCSMC express a specific panel of 11 cytokines, chemokines, and cell adhesion molecules in a time-dependent manner in response to TNF-alpha. The chip array data were supported by quantitative analysis of mRNA and protein expressions of interleukin (IL)-6, IL-8, intercellular adhesion molecule (ICAM)-1 and IL-11. The proinflammatory mediators were expressed early, whereas the anti-inflammatory cytokine IL-11 was expressed late after TNF-alpha treatment. The expression of ICAM-1 on HCCSMC increased lymphocyte adhesion to these cells, which was blocked by pretreatment with antibody to ICAM-1. TNF-alpha acted on both R(1) and R(2) receptors to induce the expression of ICAM-1. Pretreatment of HCCSMC with antisense oligonucleotides to p65 nuclear factor-kappaB (NF-kappaB) blocked the expression of ICAM-1, whereas pretreatment with antisense oligonucleotides to p50 NF-kappaB had little effect. The overexpression of p65 NF-kappaB enhanced the constitutive expression of ICAM-1, and TNF-alpha treatment had no further effect. The delayed expression of endogenous IL-11 limited the expression of ICAM-1, and pretreatment of HCCSMC with antisense oligonucleotides to IL-11 enhanced it. We conclude that TNF-alpha induces gene expression in HCCSMC for programmed synthesis and release of pro- and anti-inflammatory mediators.

Effects of acid-induced esophagitis on esophageal smooth muscle

Acid-induced esophagitis is associated with sustained longitudinal smooth muscle (LSM) contraction and consequent esophageal shortening. In addition, LSM strips from opossums with esophagitis are hyper-responsive, while the circular smooth muscle (CSM) contractility is impaired. To determine the origin of these changes, studies were performed on esophageal smooth muscle cells isolated from opossum esophagi perfused intraluminally on 3 consecutive days with either saline (control; n = 8) or HCl (n = 9). CSM and LSM cells, obtained by enzymatic digestion, were exposed to various concentrations of carbachol (CCh) and fixed. CCh induced concentration-dependent contraction of both LSM and CSM cells. CCh-induced LSM cell contraction was not different between control and esophagitis animals; however, there was marked attenuation in the CCh-induced contraction of CSM cells from esophagitis animals. Morphological studies revealed significant hypertrophy of the CSM cells. These findings suggest that impaired CSM contractility can be attributed at least in part to alterations to the CSM cell itself. In contrast, hyper-contractility demonstrated in LSM strips is likely related to factors in the surrounding tissue.

NF-kappa B activation by oxidative stress and inflammation suppresses contractility in colonic circular smooth muscle cells

BACKGROUND & AIMS

Transcription factor nuclear factor kappa B (NF-kappa B) plays a critical role in transcriptional changes in several diseases, including inflammation. The aim of this study was to investigate whether NF-kappa B is activated by inflammation and oxidative stress in colonic circular smooth muscle cells and whether that leads to suppression of their contractility.

METHODS

The experiments were performed on freshly dissociated single cells using electrophoretic mobility shift assay, Western immunoblotting, and immunofluorescence imaging.

RESULTS

The NF-kappa B DNA binding was approximately 6-fold greater in cells from the inflamed colon vs. those from the normal colon. Supershift assay indicated that the antibodies to p65, p50, and c-Rel, but not that to p52, shifted the NF-kappa B band. Western immunoblotting and immunofluorescence imaging also demonstrated the presence of p65, p50, and c-Rel proteins in the cytoplasm and their translocation to the nucleus by H(2)O(2)-induced oxidative stress. H(2)O(2) treatment degraded I kappa B(beta), but not I kappa B(alpha), to translocate NF-kappa B to the nucleus. Hydrogen peroxide concentration and time dependently activated NF-kappa B DNA binding and suppressed cell contraction to acetylcholine. NF-kappa B inhibitors significantly inhibited these effects. Inhibition of NF-kappa B prior to and during inflammation in intact dogs also reversed the suppression of contractility.

CONCLUSIONS

Transcription factor NF-kappa B is activated in colonic circular muscle cells by inflammation and oxidative stress. This activation of NF-kappa B mediates the suppression of cell contractility.

Effects of arachidonic acid on ATP-sensitive K+ current in murine colonic smooth muscle cells

The effects of arachidonic acid (AA) and the mechanism through which it modulates ATP-sensitive K+ (K(ATP)) currents were examined in single smooth muscle cells of murine proximal colon. In the current-clamping mode, AA and glibenclamide induced depolarization of membrane potential. Using 0.1 mM ATP and 140 mM K+ solution in the pipette and 90 mM K+ in the bath solution at a -80 mV of holding potential, pinacidil activated the glibenclamide-sensitive inward current. The potential of these currents was reversed to near the equilibrium potential of K+ by 60 mM K+ in the bath solution. AA inhibited K(ATP) currents in a dose-dependent manner. This inhibition was not changed when 1 mM GDPbetaS was present in the pipette. Chelerythrine, protein kinase C inhibitor, did not block the AA effects. Superoxide dismutase and metabolic inhibitors (indomethacin and nordihydroguaiacretic acid) of AA did not affect the AA-induced inhibition. Eicosatetraynoic acid, a nonmetabolizable analogue of AA, inhibited the K(ATP) currents. These results suggest that AA-induced inhibition of K(ATP) currents is not mediated by G-protein or protein kinase C activation. The inhibitory action is likely to be a possible mechanism of AA-induced membrane depolarization.

Selective modulation of PKC isozymes by inflammation in canine colonic circular muscle cells

BACKGROUND & AIMS

Protein kinase C (PKC) is a key signaling molecule in excitation-contraction coupling in several types of smooth muscle cells. We investigated whether the attenuated contraction in inflamed colon cells is caused by alterations in the expression, distribution, and activation of specific PKC isozymes.

METHODS

Kinase assays, immunofluorescence imaging, and Western immunoblotting were performed on single circular smooth muscle cells obtained from the normal dog colon as well as from colon with experimental colitis induced by mucosal exposure to ethanol and acetic acid, to determine the distribution, expression, and activation of PKC isozymes.

RESULTS

Classical (alpha, beta, and gamma), novel (delta and epsilon), and the atypical PKC (iota, lambda, and zeta) isozymes were detected in colonic circular muscle cells. The expression of PKC alpha, beta, and epsilon isozymes was down-regulated, whereas that of PKC iota and lambda isozymes was up-regulated; other isozymes were not affected by inflammation. Acetylcholine (ACh) treatment translocated only the PKC alpha, beta, and epsilon isozymes from the cytosol to the membrane in normal cells; this translocation was absent in inflamed colon cells. Immunofluorescence imaging confirmed the translocation of PKC alpha from the cytosol to the membrane in response to ACh in normal cells. PKC inhibitors, chelerythrine, and myristoylated peptides to alpha, beta, and epsilon isozymes inhibited the contractile response to ACh in normal, but not in inflamed, cells. PKC iota and lambda did not participate in the contractile response to ACh.

CONCLUSIONS

ACh-induced contraction is mediated by PKC alpha, beta, and epsilon isozymes in normal colonic circular muscle cells. Contractile dysfunction in inflamed colon cells is, in part, caused by decreased expression and impaired activation of specific PKC isozymes.

Down-regulation of L-type calcium channels in inflamed circular smooth muscle cells of the canine colon

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.