0000000000178222
AUTHOR
K. D. Süß
Muscarinic modulation of acetylcholine release: Receptor subtypes and possible mechanisms
The release of acetylcholine from central and peripheral neurones can be inhibited and facilitated by muscarine autoreceptors, i.e. receptors located on the cholinergic neurone. In the last few years evidence has accumulated that muscarine receptors are heterogeneous. This chapter describes attempts that have been made to classify the muscarine autoreceptors. In addition, some possible mechanisms behind the neuronal muscarine receptors are examined.
Control of Acetylcholine Release and of Intestinal Motility by Subtypes of Muscarine Receptors
Two types of neuronal muscarine receptors have been investigated in the myenteric plexus preparation of the guinea-pig small intestine: 1. Presynaptic receptors activation of which inhibits the depolarization-evoked release of acetylcholine. Pirenzepine and dicyclomine have low affinities to the release-inhibitory receptors (pA2 values 6.9 and 7.6) which suggests that the presynaptic receptors (similar to the smooth muscle receptors) belong to the M2 subtype. The inhibition of the electrically-evoked acetylcholine release by muscarine (0.01 - 1 μmol/1) was not affected by forskolin (1μmol/l). This indicates that cyclic AMP is not crucially involved in the muscarinic inhibition of acetylchol…