Interaction of αβ-Methylene ATP with the Cholinergic Twitch Response in the Guinea-Pig Ileum.

In this study, direct effects of the P2X purinoceptor agonist αβ-methylene ATP (αβ-meATP) and effects on the cholinergic twitch response of the electrically stimulated longitudinal muscle-myenteric plexus (LMMP) strip of the guinea-pig ileum, were investigated. αβ-meATP (1, 3, and 10 µmol/l) induced short-lasting contractions on its own, followed by an inhibition of the twitch response during its presence in the organ bath. The inhibitor of small conductance Ca2+-activated K+ (SK) channels, apamin (100 nmol/l), prevented the inhibitory effect of αβ-meATP on the twitch response, whereas tetraethylammonium (300 µmol/l), a blocker of voltage-gated K+ channels and an inhibitor at nicotinic acetylcholine receptors, augmented the inhibitory effect of αβ-meATP on the twitch response. It is concluded, that there is a functional interaction between P2X receptors and nicotinic receptors in the LMMP strip, and that a major part of the excitatory input to the cholinergic motor neuron evoking the twitch response is purinergic and not nicotinergic.