In vivo signal-transduction pathways to stimulate phasic contractions in normal and inflamed ileum

IGF-I increases IGFBP-5 and collagen alpha1(I) mRNAs by the MAPK pathway in rat intestinal smooth muscle cells

IGF-I is a potent fibrogenic growth factor that stimulates proliferation of intestinal smooth muscle cells and increases synthesis of collagen and IGF-I-binding proteins by the cells. These processes contribute to intestinal fibrosis that develops in patients with Crohn's disease and in Lewis-strain rats with experimental Crohn's disease. The aim of this study was to determine which early docking proteins are associated with IGF-I receptor signal transduction and which transduction pathway is involved in IGF-I-mediated gene regulation in intestinal smooth muscle cells. Primary cultures of smooth muscle cells isolated from the muscularis externa of the distal colon of Lewis rats were treated with IGF-I (100 ng/ml). Immunoprecipitation studies demonstrated that IGF-I stimulation resulted in tyrosine phosphorylation of IRS-1, IRS-2, and Shc. Coimmunoprecipitation demonstrated a close association between the IGF-I receptor and these three early docking proteins. Concurrent treatment with the MAPK inhibitor PD98059 (10 microM) resulted in an inhibition of the IGF-I-mediated increase in IGFBP-5 and collagen alpha(1)(I) mRNAs, while concurrent treatment with the phosphatidylinositol 3-kinase (PI3-K) inhibitor wortmannin (100 nM) had no effect. In additional experiments, cells were transiently transfected with adenoviral vectors dominantly expressing inactive mutant Akt or constitutively expressing wild-type Akt. In both cases, the IGF-I-mediated increase in collagen I protein did not differ from that observed in control cultures that had been transfected with an adenoviral vector carrying the LacZ reporter gene. These results suggest that the MAPK pathway is key to IGF-I-mediated gene regulation in intestinal smooth muscle cells, whereas data do not suggest a role for the Akt-dependent pathway in our system.

Neuronal locus and cellular signaling for stimulation of ileal giant migrating and phasic contractions

We investigated the neuronal locus, the role of PKC activation, and utilization of extracellular Ca(2+) and intracellular Ca(2+) release in smooth muscle cells for the generation of giant migrating contractions (GMCs) and rhythmic phasic contractions (RPCs) in intact normal and inflamed canine ileum. Calcitonin gene-related peptide (CGRP), administered close intra-arterially, stimulated GMCs at higher doses and RPCs at smaller doses. These effects were blocked by prior close intra-arterial infusions of CGRP(8-37), atropine, hexamethonium, and TTX but not by tachykinin, serotonin, and histaminergic receptor subtype antagonists. Both types of contractions were blocked by verapamil in normal and inflamed ileums. Dantrolene and ruthenium red blocked only the RPCs in normal ileum but blocked both GMCs and RPCs in the inflamed ileum. PKC inhibition by chelerythrine blocked GMCs only in inflamed ileum but blocked RPCs in both normal and inflamed ileums. The inhibition of phospholipase C by neomycin blocked both RPCs and GMCs in normal and inflamed ileums. In conclusion, acetylcholine is the common neurotransmitter for the stimulation of both GMCs and RPCs, but the signaling cascades for their stimulation are partially divergent, and they differ also in the normal and inflamed states.

Effect of pinaverium bromide on stress-induced colonic smooth muscle contractility disorder in rats

AIM

To investigate the effect of pinaverium bromide, a L-type calcium channel blocker with selectivity for the gastrointestinal tract on contractile activity of colonic circular smooth muscle in normal or cold-restraint stressed rats and its possible mechanism.

METHODS

Cold-restraint stress was conducted on rats to increase fecal pellets output. Each isolated colonic circular muscle strip was suspended in a tissue chamber containing warm oxygenated Tyrode-Ringer solution. The contractile response to ACh or KCl was measured isometrically on ink-writing recorder. Incubated muscle in different concentrations of pinaverium and the effects of pinaverium were investigated on ACh or KCl-induced contraction. Colon smooth muscle cells were cultured from rats and (Ca(2+))(i) was measured in cell suspension using the Ca(2+) fluorescent dye fura-2/AM.

RESULTS

During stress, rats fecal pellet output increased 61 % (P<0.01). Stimulated with ACh or KCl, the muscle contractility was higher in stress than that in control. Pinaverium inhibited the increment of (Ca(2+))(i) and the muscle contraction in response to ACh or KCl in a dose dependent manner. A significant inhibition of pinaverium to ACh or KCl induced (Ca(2+))(i) increment was observed at 10(-6) mol/L. The IC(50) values for inhibition of ACh induced contraction for the stress and control group were 1.66X10(-6) mol/L and 0.91X10(-6) mol/L, respectively. The IC(50) values for inhibition of KCl induced contraction for the stress and control group were 8.13X10(-7) mol/L and 3.80X10(-7) mol/L, respectively.

CONCLUSION

Increase in (Ca(2+))(i) of smooth muscle cells is directly related to the generation of contraction force in colon. L-type Ca(2+) channels represent the main route of Ca(2+) entry. Pinaverium inhibits the calcium influx through L-type channels; decreases the contractile response to many kinds of agonists and regulates the stress-induced colon hypermotility.

Different types of contractions in rat colon and their modulation by oxidative stress

The aim of this study was to investigate the modulation of in vitro rat colonic circular muscle contractions by dextran sodium sulfate (DSS)-induced inflammation and in spontaneous inflammation in HLA-B27 rats. We also examined the potential role of hydrogen peroxide (H(2)O(2)) in modulating excitation-contraction coupling. The muscle strips from the middle colon generated spontaneous phasic contractions and giant contractions (GCs), the proximal colon strips generated primarily phasic contractions, and the distal colon strips were mostly quiescent. The spontaneous phasic contractions and GCs were not affected by inflammation, but the response to ACh was suppressed in DSS-treated rats and in HLA-B27 rats. H(2)O(2) production was increased in the muscularis of the inflamed colon. Incubation of colonic muscle strips with H(2)O(2) suppressed the spontaneous phasic contractions and concentration and time dependently reduced the response to ACh; in the middle colon, it also increased the frequency of GCs. We conclude that H(2)O(2) mimics the suppression of the contractile response to ACh in inflammation. H(2)O(2) also selectively suppresses phasic contractions and increases the frequency of GCs, as found previously in inflamed dog and human colons.

In vivo changes in the intestinal reflexes and the response to CCK in the inflamed small intestine of the rat

Functional motor changes and morphological alterations have been associated with intestinal inflammation. The aim of our study was to evaluate functional alterations of intestinal reflexes and of the responses to CCK in the Trichinella spiralis model of intestinal inflammation. Rats were prepared with strain gauges and electrodes in the small intestine to evaluate spontaneous motor activity, the ascending contraction of the peristaltic reflex, and the motor responses to CCK-8 infusion. Infected animals showed increased motor activity at the duodenum and jejunum but not at the ileum. Ascending contraction was increased in both duodenum and ileum. Ascending excitation after N(omega)-nitro-L-arginine was still increased as well as the residual response after atropine. Response to CCK-8 during intestinal inflammation was changed in the jejunum, in which it turned from the inhibition shown in healthy animals to excitation. NADPH-diaphorase staining did not show any changes between distribution and density of positive neurons in either healthy or infected animals. In conclusion, intestinal inflammation induces functional changes in the motor activity that could explain the abnormal motor responses observed in inflammatory disorders.

Enteric locus of action of prokinetics: ABT-229, motilin, and erythromycin

We investigated the in vivo and in vitro locus of actions of prokinetics: motilin, erythromycin, and ABT-229. The test substances were infused close intra-arterially in short segments of the jejunum in the intact conscious state. Each prokinetic acted on a presynaptic neuron and utilized at least one nicotinic synapse to stimulate circular muscle contractions. The final neurotransmitter at the neuroeffector junction was ACh. Motilin and erythromycin, but not ABT-229, also released nitric oxide. Each prokinetic utilized somewhat different subtypes of muscarinic, serotonergic, tachykininergic, and histaminergic receptors, except for the M(3) receptor, which was common to all of them. In contrast, none of the prokinetics stimulated contractions in mucosa-free or mucosa-attached muscle strips, or rings, even though methacholine or electrical field stimulation induced phasic contractions in all of them. The prokinetics also did not release ACh in longitudinal muscle-myenteric plexus preparations. Each prokinetic, however, decreased the length of enzymatically dispersed single cells. In conclusion, each prokinetic may act on a different subset of presynaptic neurons that converge on the postsynaptic cholinergic and nonadrenergic noncholinergic motoneurons. The presynaptic neurons may be impaired in the muscle bath environment.