Effects of tetrodotoxin, Ca2+ absence, d-tubocurarine and vesamicol on spontaneous acetylcholine release from rat muscle

An expansion of Simons' integrated hypothesis of trigger point formation

Simons' integrated hypothesis proposed a model of trigger point (TrP) activation to explain known TrP phenomena, particularly endplate noise. We propose an expansion of this hypothesis to account for new experimental data and established muscle pathophysiology.

The effects of brucine and alcuronium on the inhibition of [3H]acetylcholine release from rat striatum by muscarinic receptor agonists

1. Radioligand binding experiments indicate that the affinity of muscarinic receptors for their agonists may be enhanced by allosteric modulators. We have now investigated if brucine can enhance the inhibitory effects of muscarinic receptor agonists on the electrically evoked release of [3H]acetylcholine ([3H]ACh) from superfused slices of rat striatum. 2. The evoked release of [3H]ACh was inhibited by all agonists tested (i.e., furmethide, oxotremorine-M, bethanechol and oxotremorine). 3. Brucine enhanced the inhibitory effects of furmethide, oxotremorine-M and bethanechol on the evoked [3H]ACh release without altering the inhibitory effect of oxotremorine. 4. Alcuronium was applied for comparison and found to diminish the inhibitory effect of furmethide on the evoked [3H]ACh release. 5. The results demonstrate that it is possible both to enhance and diminish the functional effects of muscarinic receptor agonists by allosteric modulators. 6. The direction of the observed effects of brucine and alcuronium on [3H]ACh release fully agrees with the effects of these modulators on the affinities of human M4 receptors for furmethide, oxotremorine-M, bethanechol and oxotremorine, as described by Jakubik et al. (1997). This supports the view that the presynaptic muscarinic receptors responsible for the autoinhibition of ACh release in rat striatum belong to the M4 muscarinic receptor subtype.

Spontaneous release of acetylcholine from Torpedo synaptosomes: effect of cetiedil and its analogue MR 16728

The effects of cetiedil and its analogue MR 16728 were examined on spontaneous acetylcholine release measured with a chemiluminescent assay using choline oxidase in a synaptosomal suspension obtained from Torpedo marmorata electric organ. Evoked acetylcholine release is inhibited by cetiedil, whereas this drug enhances spontaneous extracellular Ca(2+)-independent acetylcholine release (up to 340%). This effect was examined as a function of cetiedil concentration and incubation time. On the other hand, the analogue MR 16728, which enhances A23187-evoked acetylcholine release, also enhances spontaneous Ca(2+)-independent acetylcholine release. Cetiedil and MR 16728 effects on spontaneous acetylcholine release were also examined in the presence of Ca2+. Addition of Ca2+ enhanced spontaneous acetylcholine release by 75%, and cetiedil and MR 16728 stimulation was maintained but with different levels of enhancement. Thus, these results show that the processes responsible for evoked and spontaneous acetylcholine release are sensitive but in different ways to drugs of the cetiedil family.