Properties of acetylcholine-induced relaxation of smooth muscle isolated from the proximal colon of the guinea-pig

Abstract

The properties of mechanical responses elicited by stimulation with acetylcholine (ACh) were investigated in circular smooth muscle preparations isolated from the proximal colon of guinea-pig. Application of ACh (10 -8 -10 -6 M) for 3-5 min produced a biphasic response, with an initial contraction followed by a relaxation. Atropine inhibited the initial contraction, while N ω -nitro-L-arginine (L-NA) inhibited the relaxation, suggesting that the former was produced by activation of muscarinic receptors while the latter was produced by an elevated production of nitric oxide (NO). In the presence of atropine, the ACh-relaxation was attenuated by removal of the mucosa and abolished by removal of both submucosal and mucosal layers. The ACh-induced relaxation was also attenuated by either tetrodotoxin (TTX, 3 × 10 -7 M) or hexamethonium (10 -6 M). In the presence of atropine, transmural nerve stimulation (TNS) elicited a biphasic response, with an initial phasic contraction followed by a relaxation. The amplitude of TNS-induced relaxation was significantly reduced by hexamethonium or L-NA and was abolished by TTX. Both ACh and TNS produced relaxation in preparations isolated from the proximal colon, but not in those from the middle part of colon. Immunohistochemistry for neuronal nitric oxide synthase revealed no difference in the distribution of nitrergic nerves between the proximal and middle part of the colon, with nitrergic nerves in both the mucosal and submucosal layers as well as in the smooth muscle and myenteric layers. These results suggest that ACh induces NO production by excitation of postganglionic nerves distributed mainly in the mucosal and submucosal layers. In circular smooth muscle preparations isolated from the middle part of colon, ACh or TNS produced contractile responses alone, with no associated relaxation, suggesting that the ACh-activated postganglionic nitrergic nerves are distributed in the mucosal and submucosal layers of the proximal colon but not in the middle part of the colon.

Properties of spontaneous contractions and their modulation by transmural nerve stimulation in circular smooth muscle isolated from the pacemaker area in the flexure region of the guinea-pig colon

“…From these results, it was deduced that pacemaker cells and possibly the related smooth muscle cells contributing to the large contractions were innervated by cholinergic excitatory nerves, nitrergic inhibitory nerves, substance P-ergic excitatory nerves and NANCNN inhibitory nerves. These results agree with the type of neurons involved in gastrointestinal smooth muscle tissue (Hoyle and Burnstock, 1989;Furness et al, 1994;Kuriyama et al, 1998;Kunze and Furness 1999;Furness, 2000;Lomax and Furness, 2000), and were also in agreement with the results examined in the proximal region but not the pacemaker area of the guinea-pig colon (Kodama et al, 2010). The density of the nerves distributed in individual preparations seemed to be non-homogenous, and in general the former two were high, compared to the latter two.…”

“…The pacemaker area has both ICC-MP distributed in the myenteric layer and ICC-SMP distributed in the submucosal layer (Kobayashi et al, 1996;Nahar et al, 1998), in addition to ICC-IM in both the circular and longitudinal smooth muscle layers (Toma et al, 1999). The removal of the longitudinal smooth muscle layer is associated with the loss of the myenteric layer from the circular smooth muscle layer (Kodama et al, 2010). Thus, the preparations which had the submucosal layer removed contained only ICC-MP, which produced the large contractions.…”

Further evidence of endogenous hydrogen sulphide as a mediator of relaxation in human and rat bladder

“…KCl, adrenergic and cholinergic agonists would usually be chosen to precontract smooth muscle in not only LUT but also cardiovascular vessels, gastrointestinal tract, and corpus cavernosum tissues. 2,5,6,7,23,24 Taken together, we proposed that the effect of H 2 S on human and rat bladder smooth muscle tone might play various roles, depending on different pretreatments. 20,21 In our study, exogenous and endogenous H 2 S relaxed smooth muscle that was pre-contracted with acetylcholine chloride.…”

Ultrastructural characterization of interstitial cells of Cajal associated with the submucosal plexus in the proximal colon of the guinea pig

“…ICC-SMP have been widely acknowledged as the primary pacemaker, together with ICC-MP as the secondary pacemaker. Preparations created after removal of the submucosa do not exhibit slow waves (Smith et al 1987;Plujà et al 2001) or rhythmic contraction (Yoneda et al 2004;Kodama et al 2010) attributable to ICC-SMP.…”