Effects of nicotine, dimethylphenylpiperazinium and tetramethylammonium onsmooth muscles from feline and human gastric corpus

Both excitatory and inhibitory intrinsic neurons could be found within the gastric wall, both of them receiving innervation from vagal fibres and bein g sensitive to nicotine. The effects of three nicotine receptor agonists, n icotine, tetramethylammonium (TMA) and 1,1-dimethyl-4-phenylpiperazinium (D MPP), on contractile activity of preparations isolated from feline and huma n gastric corpus wall were investigated. While DMPP (3.5 x 10(-8) to 5.9 X 10(-4) M) did not affect either spontaneous contractions or basal tension o f isolated preparations from both species, TMA produced concentration-depen dent tonic contractions of both circular and longitudinal isolated preparat ions from human (3.66 x 10(-5) to 5.10 X 10(-3) M) and feline (6.1 X 10(-7) to 2.1 X 10(-3) M) stomach. On the other hand, nicotine (4.1 X 10(-8) to 7 .0 X 10(-4) M) produced concentration-dependent relaxation of only circular isolated preparations from feline gastric corpus. The effect of nicotine w as sensitive to mecamylamine, and not to pancuronium, while the effect of T MA was sensitive to both mecamylamine and pancuronium. Although in our expe riments DMPP had no effect, its excitatory action on gastric intrinsic neur ons through the hexamethonium-insensitive pathway had already been describe d. The results of our study suggest that two different types of ganglion ni cotine receptor exist together within the wall of feline stomach: (1) type N-N1 which is involved in relaxation and is sensitive only to nicotine and mecamylamine, and not to DMPP, TMA and pancuronium; (2) and type N-N2 which is involved in contraction of gastric muscle and sensitive to DMPP, TMA, m ecamylamine and pancuronium, and not to nicotine. (C) 2000 Academic Press.