ISSN:
1432-1912
Keywords:
Key words BIMU 8
;
BIMU 1
;
Renzapride
;
5-HT4 receptors
;
Acetylcholine release
;
Myenteric plexus
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Abstract The effects of the 5-HT4 receptor agonists BIMU 8, BIMU 1, renzapride and of the 5-HT1p receptor agonist 5-hydroxyindalpine on basal and electrically evoked outflow of tritium were studied in guinea-pig longitudinal muscle myenteric plexus preparations preincubated with [3H]choline. Muscle contractions were recorded simultaneously. BIMU 8 caused a calcium dependent and tetrodotoxin sensitive increase in basal [3H]outflow that was assumed to represent release of [3H]acetylcholine. In addition, BIMU 8 enhanced the release of [3H]acetylcholine and twitch contractions evoked by submaximal electrical stimulation. Ondansetron (1 μmol/l) did not change the effects of BIMU 8, but DAU 6285 and tropisetron (each 1 μmol/l) competitively antagonized the various facilitatory effects of BIMU 8 with pA2 values of 7.0–7.2 (DAU 6285) and 7.0–7.3 (tropisetron). The phosphodiesterase inhibitors IBMX and rolipram did not increase the effects of BIMU 8. BIMU 1 and renzapride also concentration-dependently increased basal release of acetylcholine, and release and contractions caused by submaximal stimulation. The effects of BIMU 1 and renzapride were competitively antagonized by 1 μmol/l tropisetron (pA2 6.6–7.1). The EC50 values for the increase in the evoked [3H]acetylcholine release and contractions were closely similar. 5-Hydroxyindalpine did not change basal release and slightly inhibited the evoked release of [3H]acetylcholine. Release of acetylcholine and contractions elicited by submaximal stimulation were strongly inhibited by (+)-tubocurarine which indicates that nicotinic ganglionic transmission is involved in this kind of release. The results suggest that BIMU 8, BIMU 1 and renzapride stimulate 5-HT4 receptors at cholinergic interneurones and thereby facilitate nicotinic ganglionic transmission in the myenteric plexus. Cyclic AMP is probably not involved in the 5-HT4 receptor mediated facilitation of acetylcholine release.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00233241
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