Participation of muscarinic acetylcholine receptors in nitric oxide pathway in cat duodenum.

The effect of activation of muscarinic acetylcholine subtype M1 receptors on the electrical field stimulation (EFS)-induced contractions in cat duodenal muscle strips was investigated. EFS elicited two types of responses: a) on-contraction; and b) off-contraction. The EFS-evoked responses were tetrodotoxin- and atropine-sensitive. In all strips the muscarinic acetylcholine subtype M1 agonist (4-Hydroxy-2-butynyl)-1-trimethylammonium-m-chlorocarbanilate chloride (McN-A-343) increased the tone and the amplitude of the spontaneous contractions. On this background EFS produced an inhibition of the phasic contractions at switching on the stimulation, followed by off-contractions. The EFS-induced inhibition was removed by N omega-nitro-L-arginine and was partly overcome by L-arginine. The results suggest the participation of muscarinic acetylcholine subtipe M1 receptors in the mediation of nitrergic inhibitory responses in cat duodenum.