Muscarinic presynaptic inhibition of synaptic transmission in myenteric plexus of guinea‐pig ileum.

Abstract

The effect of oxotremorine (300 pM to 30 nM) synaptic transmission in isolated myenteric ganglia of guinea pig ileum was investigated with intracellular recording techniques. These low concentrations of oxotremorine had no effect on the resting membrane potentials or on the membrane conductance. Oxotremorine reduced the amplitude of the fast excitatory post-synaptic potential (epsp) but did not reduce the amplitude of nicotinic responses to ionophoretic application of acetylcholine (ACh). This effect of oxotremorine on the fast epsp was dose-dependent; the amplitude was reduced by about 45% by 30 nM-odotremorine. Non-cholinergic slow epsp evoked by repetitive presynaptic nerve stimulation were reduced in amplitude by oxotremorine. Hyoscine or atropine (1 nM) completely antagonized both these effects of oxotremorine (30 nM). Muscarinic antagonists alone increased the amplitude of second and subsequent fast epsp when these were evoked at intervals of 1 s, and increased the amplitude and duration of the slow epsp evoked by repetitive presynaptic nerve stimulation. Muscarinic receptor activation evidently inhibits the release of the transmitters which mediate both the fast and the slow epsp and that this can occur with physiologically released ACh during repetitive presynaptic nerve activity.