Relaxation of rat distal colon by activation of muscarinic, neuronal receptors: possible involvement of P(2y)-purinoceptors

Muscarinic receptor subtypes involved in regulation of colonic motility in mice: functional studies using muscarinic receptor-deficient mice

Although muscarinic M(2) and M(3) receptors are known to be important for regulation of gastric and small intestinal motility, muscarinic receptor subtypes regulating colonic function remain to be investigated. The aim of this study was to characterize muscarinic receptors involved in regulation of colonic contractility. M(2) and/or M(3) receptor knockout (KO) and wild-type mice were used in in vivo (defecation, colonic propulsion) and in vitro (contraction) experiments. Amount of feces was significantly decreased in M(3)R-KO and M(2)/M(3)R-KO mice but not in M(2)R-KO mice. Ranking of colonic propulsion was wild-type=M(2)R-KO>M(3)R-KO>M(2)/M(3)R-KO. In vitro, the amplitude of migrating motor complexes in M(2)R-KO, M(3)R-KO and M(2)/M(3)R-KO mice was significantly lower than that in wild-type mice. Carbachol caused concentration-dependent contraction of the proximal colon and distal colon from wild-type mice. In M(2)R-KO mice, the concentration-contraction curves shifted to the right and downward. In contrast, carbachol caused non-sustained contraction and relaxation in M(3)R-KO mice depending on its concentration. Carbachol did not cause contraction but instead caused relaxation of colonic strips from M(2)/M(3)R-KO mice. 4-[[[(3-chlorophenyl)amino]carbonyl]oxy]-N,N,N-trimethyl-2-butyn-1-aminium chloride (McN-A-343) caused a non-sustained contraction of colonic strips from wild-type mice, and this contraction was changed to a sustained contraction by tetrodotoxin, pirenzepine and L-nitroarginine methylester (L-NAME). In the colon of M(2)/M(3)R-KO mice, McN-A-343 caused only relaxation, which was decreased by tetrodotoxin, pirenzepine and L-NAME. In conclusion, M(1), M(2) and M(3) receptors regulate colonic motility of the mouse. M(2) and M(3) receptors mediate cholinergic contraction, but M(1) receptors on inhibitory nitrergic nerves counteract muscarinic contraction.

Neurogenic and non-neurogenic mechanisms in response of rat distal colon muscle to dextran sulphate sodium treatment

We studied, by organ bath methodology, how experimental colitis in rat, induced by the administration of dextran sulphate sodium (DSS) in the drinking water (3% for 3 or 7 days, or 5% for 7 days; Controls received ordinary tap water), may influence spontaneous, contractile activity of the longitudinal muscle layer. DSS treatment caused a dose-dependent increase in phasic contractile activity of the colon muscle. This effect needed an optimal preload of the tissues to be evident, and was non-neurogenic (i.e. myogenic and/or paracrine) in nature. Moreover, the DSS treatment appeared to impair a neurogenic, nitric oxide (NO)-dependent, relaxant response to the stretch (i.e. preload) applied to the tissues. Inducible NO synthase was localized by immunohistochemistry to infiltrating mononuclear cells in the colon wall. We propose that NO, via the inducible pathway, exerts marked effects on the neuromuscular apparatus in the DSS model of experimental colitis.

M1 receptor-mediated nitric oxide-dependent relaxation unmasked in stomach fundus from M3 receptor knockout mice

Muscarinic receptors can mediate both contractile and relaxant responses in smooth muscle. The stomach fundus from wild-type mice possesses a neuronal M(1) receptor that mediates relaxation to carbamylcholine and (4-hydroxy-2-butynyl)-1-trimethylammonium-3-chlorocarbanilate chloride (McN-A-343) but is masked by M(3) receptor-mediated contraction to both agonists. When the M(3) receptor was deleted, cholinergic-induced relaxation was unmasked. M(1) receptor antagonism with pirenzepine, nitric oxide (NO) synthase inhibition with N(omega)-nitro-L-arginine methyl ester hydrochloride, and inhibition of neuronal activation with tetrodotoxin abolished relaxation to McN-A-343 in tissues from M(3) receptor knockout mice, supporting the neuronal localization of an M(1) receptor that activated NO release to effect relaxation. However, the cyclooxygenase inhibitor indomethacin did not affect contraction or relaxation to carbamylcholine in stomach fundus from wild-type or M(3) receptor knockout mice, indicating that cyclooxygenase products played no role in these responses. The neuronal M(1) receptor modulated relaxation induced by carbamylcholine and McN-A-343 but not relaxation induced by electric field stimulation of the stomach fundus. These data support the presence of M(1) receptor-mediated relaxation in the stomach and suggest that when the M(3) receptor is eliminated or blocked, M(1) receptor-mediated gastric relaxation may be enhanced, possibly leading to alterations in gastric emptying and subsequent effects on body weight.

Functional effects of dextran sulphate sodium (DSS) treatment on the longitudinal muscle of rat distal colon

1. The current study addressed how acute colitis, induced in male Sprague-Dawley rats by the administration of dextran sulphate sodium (DSS) in their drinking water, may affect some functional properties of the longitudinal muscle layer of the distal colon. 2. Dextran sulphate sodium was provided at a concentration of 3% for 3 or 7 days, or 5% for 7 days, and the rats were thereafter killed. Specimens of the distal colon were taken for histology or for organ bath experiments. 3. The colitis score increased significantly with increasing dose of DSS administered. At 5% concentration, there was sometimes even transmural inflammation. Functionally, there was a progressive increase in optimal preload (P(o)) for the contractile response to carbachol (1 microM), in relation to the severity of the colitis. At 5% DSS, the magnitude of the response to carbachol at P(o) was significantly increased compared with control rats. Such an effect could not be verified when, instead, K+ (60 mM) was used as a spasmogen. 4. It is concluded, that the colitis score increased in severity progressively with increasing amounts of DSS administered. The longitudinal muscle layer was functionally affected by the inflammation. Thus, there was a progressive increase in optimal preload for muscle contraction. Moreover, severe colitis resulted in an increase of the contractile response to carbachol, while a significant increase in the response to depolarization with K+ could not be found.