Effects of paralytic shellfish poison on acetylcholine release from the myenteric plexus of guinea pig

We examined the mechanism of inhibition of acetylcholine (ACh) release by gonyautoxins (GTXs) in the longitudinal muscle strip preparation of guinea pig ileum. The preparation was placed in an organ-bath and immersed in Tyrode solution at a temperature of 37.0°C. ACh release from the myenteric plexus of the longitudinal muscle was determined by using Palton's method. When the control Tyrode solution was replaced by the test solution containing GTXs (0.5MU/ml), spontaneous release of ACh was suppressed about 60% of the control value. GTXs completely inhibited ACh release induced by the application of nicotine (2.0μg/ml) or electrical stimuli (1 or 10Hz), whereas they did not affect ACh release evoked by the application of potassium-rich Tyrode solution (50mM). These results suggest that GTXs might suppress the impulse conduction of the post-synaptic neuron in the myenteric plexus.