Effects of three mammalian tachykinins on single enteric neurons.

The effects of substance P (SP), substance K (SK) and neuromedin K (NMK) were compared on single neurons of the guinea pig myenteric plexus. The tachykinins depolarized all myenteric neurons with a rank order of potency SP greater than SK greater than NMK. In approximately 80% of neurons studies the depolarization was associated with an increase in membrane resistance: in 20% membrane resistance decreased. The depolarizations were not affected by tetrodotoxin (TTX) (300 nM), hyoscine (1 microM) or by [D-Arg1, D-Pro2, D-Trp7,9, Leu11]SP (1 microM). These results provide no evidence for more than one type of tachykinin receptor on myenteric neurons.