ISSN:
1432-1912
Keywords:
Key words Endogenous acetylcholine release
;
Guinea-pig trachea
;
HPLC-ECD
;
Prejunctional muscarinic autoreceptor
;
Autoinhibition
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Abstract We investigated the effects of the full muscarinic acetylcholine receptor agonist methacholine and the partial and putatively M2-selective agonist pilocarpine on endogenous acetylcholine release from guinea-pig trachea by use of high-performance liquid chromatography with electrochemical detection. Atropine-induced increases in acetylcholine release were used to monitor the system. Electrical field stimulation (8 V, 30 Hz, 0.5 ms for 5 min)-induced acetylcholine release in the presence of neostigmine, with or without preincubation with choline to maximally enhance acetylcholine output, was increased to about 225% by 0.3 μM atropine, indicating functional autoinhibition. However, methacholine (10 μM) did not affect the acetylcholine release, whereas it was enhanced to 166% by 30 μM pilocarpine. When electrical field stimulation was applied at lower intensity (8 V, 16 Hz, 0.1 ms for 5 min) and in the absence of neostigmine, an increase by 0.3 μM atropine (to 177%) but a decrease of the acetylcholine release by 10 μM methacholine (to 65%) and 30 μM pilocarpine (to 63%) were observed. These results clearly demonstrate (i) that inhibition of evoked endogenous acetylcholine release from prejunctional nerve terminals in guinea-pig trachea can only be demonstrated under conditions of low junctional concentrations of acetylcholine, and (ii) that pilocarpine, as a partial muscarinic agonist, behaves as an antagonist under high junctional concentrations of the neurotransmitter.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00170835
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