[Actions of endogenous hydrogen sulfide on colonic hypermotility in a rat model of chronic stress].

The present study was designed to investigate the potential role of endogenous hydrogen sulfide (H2S) in chronic stress-induced colonic hypermotility. Male Wistar rats were submitted daily to 1 h of water avoidance stress (WAS) or sham WAS (SWAS) for 10 consecutive days. The total number of fecal pellets was counted at the end of each 1 h of WAS or SWAS session. Organ bath recordings were used to test the colonic motility. H2S production of colon was determined, and immunohistochemistry and Western blot were performed on rat colonic samples to detect the distribution and expression of H2S-producing enzymes. The results showed that i) repeated WAS increased the number of fecal pellets per hour and the area under the curve (AUC) of the spontaneous contractions of colonic strips (P < 0.05), ii) repeated WAS decreased the endogenous production of H2S and the expression of H2S-producing enzymes in the colon devoid of mucosa and submucosa (P < 0.001), iii) cystathionine-γ-lyase (CSE) was strongly expressed in the cytosols of the circular and longitudinal smooth muscle cells and the nucleus of the myenteric plexus neurons, iv) cystathionine-ß-synthase (CBS) was primarily localized in the cytosols of myenteric plexus neurons and weakly localized in the epithelial cells and v) inhibitors of H2S-producing enzymes increased the contractile activity of colonic strips in the SWAS rats (P < 0.001). In conclusion, the results suggest that the colonic hypermotility induced by repeated WAS may be associated with the decreased production of endogenous H2S.

[Effects of methane on proximal colon motility of rats and ion channel mechanisms].

OBJECTIVE: To explore the effects of methane on proximal colon motility and elucidate its ion channel mechanisms. METHODS: The circular muscle and longitudinal muscle strips of proximal colon were isolated from rats. An isometric force transducer and a biology signal collection system were employed to observe the effects of methane on spontaneous contractile activity of muscle strips. The effects of methane on longitudinal muscle strips were observed after pre-treatment of these strips with tetrodotoxin (TTX) or N-nitro-L-arginine methylester (L-NAME). Single cell of colonic smooth muscle was isolated by collagenase and then whole-cell patch clamp technique was used to record voltage dependent potassium current (IKV) and large conductance Ca(2+)-activated K(+) current (IBKca) in the absence or presence of methane. RESULTS: Methane significantly attenuated the contractile amplitude of longitudinal muscle strips (from (1.12 ± 0.27) to (0.99 ± 0.31) g, n = 19, P = 0.013) whereas there were no changes in some longitudinal muscle strips (n = 6) in the presence of methane. The inhibitory effect of methane persisted after the pre-treatment of longitudinal muscle strips with TTX or L-NAME. Methane had no effects on the contractile cycle time of longitudinal muscle strips and contractile activity of circular muscle strips. And 3% methane solution significantly increased the density of IKV (from (13.3 ± 1.0) pA/pF to (18.5 ± 1.4) pA/pF, at +60 mV, n = 11, P = 0.001) versus the control group whereas methane had no effect on IBKca (all P > 0.05). CONCLUSION: Methane can inhibit contractile activity of proximal colonic longitudinal muscle by activating voltage dependent potassium channel and increasing IKV.

[Effects of cholecystokinin octapeptide on the contractile activity of guinea-pig colonic smooth muscles, L-type calcium currents and membrane potentials of myocytes].

OBJECTIVE: To investigate the effects and mechanism of cholecystokinin octapeptide (CCK-8S) on the contractile activity of smooth muscles, L-type calcium current and membrane potentials of proximal colon myocytes in guinea pig. METHODS: (1) Strips of proximal colon were obtained from adult guinea pigs. The contraction of these stripes was measured by a RM6240 multi-channel physiological signal system. (2) Suspension of single smooth muscle cells (SMCs) were obtained from proximal colon and isolated by enzymatic digestion. The effect of CCK-8S on intracellular calcium concentration ([Ca(2+)]i) of SMCs was examined by fura-2-loaded microfluorimetric measurement. (3) Resting potential (RP), action potential (AP) and L-type calcium current (I(Ca-L)) were recorded by patch-clamp technique. RESULTS: (1) The contractile amplitude and frequency of muscle stripes enhanced by CCK-8S (10(-7) mol/L) were (149 ± 12)% and (132 ± 13)% respectively of those of control group (all P < 0.05). They were significantly attenuated by pretreating strips with CCK1 receptor antagonist devazepide (10(-7) mol/L), L-type calcium channel blocker nifedipine (10(-5) mol/L), Ca(2+)-ATPase inhibitor TG (thapsigargin) (10(-5) mol/L) and BA (boric acid) (10(-5) mol/L) respectively. (2) [Ca(2+)]i of SMCs intensified by CCK-8S was (738 ± 24)% of that of control group. And it was inhibited by pretreating SMCs with devazepide (all P < 0.05). (3) After the superfusion of CCK-8S, RP depolarized to (52 ± 9)%, the exogenously stimulated peak values of AP rose to (140 ± 4)% and fast repolarization time of AP decreased to (61 ± 13)% (all P < 0.05). They were significantly inhibited when these cells were pretreated with devazepide and/or nifedipine (n = 8, P < 0.05 for each group) whereas CI 988 had little effect. (4) The CCK-8S-evoked I(Ca-L) of SMCs at the voltage of + 10 mV was boosted to (138 ± 7)%. Such an effect was suppressed by a pretreatment with nifedipine, devazepide, TG and BA respectively. In the presence of an inhibitor of inositol 1,4,5-trisphosphate (IP3) receptors, heparin (10(-6) mol/L) and an protein kinase C (PKC) inhibitor, saurosporine (10(-6) mol/L), CCK-8S did not significantly intensify I(Ca-L) (all P > 0.05). CONCLUSION: CCK-8S promotes proximal colon contraction by CCK1 receptors through the activation of IP3-mediated PKC pathway.