Mobilization of the readily releasable pool of acetylcholine from a sympathetic ganglion by tityustoxin in the presence of vesamicol

The present experiments tested whether preganglionic stimulation and direct depolarization of nerve terminals by tityustoxin could mobilize similar or different pools of acetylcholine (ACh) from the cat superior cervical ganglia in the presence of 2-(4-phenylpiperidino)cyclohexanol (vesamicol, AH5183), an inhibitor of ACh uptake into synaptic vesicles. In the absence of vesamicol, both nerve stimulation and tityustoxin increased ACh release. In the presence of vesamicol, the release of ACh induced by tityustoxin was inhibited, and just 16% of the initial tissue content could be released, a result similar to that obtained with electrical stimulation under the same condition. When the impulse-releasable pool of ACh had been depleted, tityustoxin still could release transmitter, amounting to some 10% of the ganglion's initial content. This pool of transmitter seemed to be preformed in the synaptic vesicles, rather than synthesized in response to stimuli, as tityustoxin could not release newly synthesized [3H]ACh formed in the presence of vesamicol, and hemicholinium-3 did not prevent the toxin-induced release. In contrast to the results with tityustoxin, preganglionic stimulation could not release transmitter when impulse-releasable or toxin-releasable compartments had been depleted. Our results confirm that vesamicol inhibits the mobilization of transmitter from a reserve to a more readily releasable pool, and they also suggest that, under these experimental conditions, there might be some futile transmitter mobilization, apparently to sites other than nerve terminal active zones.

Effects of tityustoxin and ouabain on release of acetylcholine from slices of cortex from the rat brain and on the acetylcholine content of cytoplasmic and crude vesicular fractions

In this paper, the effects of tityustoxin and ouabain on the release and mobilization of ACh from cytoplasmic and vesicular stores of slices of cortex from the brain of the rat are described. Tityustoxin induced an increase of release of ACh which was time-dependent and this effect was accompanied by a concomitant decrease of the ACh, measured in cytoplasmic and crude vesicular fractions. Unlike tityustoxin, ouabain did not increase the release and synthesis of ACh during a 2 min period of stimulation but later, at 5, 10 and 15 min, ouabain increased the release and synthesis of ACh from incubated slices of cortex. After 10 min, ouabain caused a reduction of the content of ACh from cytoplasmic and crude vesicular fractions.

The effect of 2-(4-phenylpiperidino)cyclohexanol (AH-5183), tityustoxin and ouabain on the release of acetylcholine and its mobilization from cytoplasmic and vesicular pools of rat brain cortical slices

The effect of vesicular acetylcholine (ACh) transport blocker 2-(4-phenylpiperidino)cyclohexanol (AH-5183) on the subcellular storage and release of ACh was studied in rat brain cortical slices. AH-5183 reduced the release of ACh from cortical slices stimulated by tityustoxin and ouabain. Tissue stimulated in the presence of AH-5183 contained more ACh in both the nerve terminal synaptic vesicles and cytoplasmic fraction than did tissue stimulated in drug's absence. Thus, AH-5183 blocked the tityustoxin and ouabain induced release of ACh from both cytoplasmic and vesicular pools. AH-5183 also depressed the spontaneous release of ACh from incubated slices and, in this condition, the drug had no effect in the subcellular distribution of ACh. It is suggested that AH-5183 interferes with the process of ACh release independent of its blocking action on ACh transport into the synaptic vesicles.

Choline oxidase chemiluminescent assay, after removal of eserine from medium, of acetylcholine released in vitro from brain slices

A chemiluminescent method has been used recently for the determination of acetylcholine with limitations such as the presence of a cholinesterase inhibitor in the incubation medium, which is indispensable for the study of acetylcholine release by various agents. A modified procedure is presented in which the cholinesterase inhibitor eserine (physostigmine) is extracted from the medium. The results showed complete recovery when labelled acetylcholine was used. This modified procedure was used to determine the release of acetylcholine evoked by tityustoxin and ouabain. The results were comparable to those obtained by bioassay using a strip of guinea pig ileum.