Mechanisms of the release of 3H-noradrenaline by dimethylphenylpiperazinium (DMPP) in the rat vas deferens |
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Authors: | M Niebler U Trendelenburg |
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Institution: | (1) Institut für Pharmakologie und Toxikologie, Universität Würzburg, Versbacher Strasse 9, D-8700 Wurzburg, Federal Republic of Germany |
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Abstract: | Summary In the rat vas deferens, DMPP is a substrate of uptake, (Krn = 11.5 mol/I). After block of vesicular uptake, monoamine oxidase and catechol-O-methyl transferase, after loading of the tissue with 3H-noradrenaline, and in calcium-free solution (i. e., when axoplasmic 3H-noradrenaline levels were high and when depolarization-induced exocytotic release was impossible), DMPP induced a pronounced outward transport of 3H-noradrenaline. On the other hand, when, in similar experiments, vesicular uptake and monoamine oxidase were intact (i.e., when axoplasmic 3H-noradrenaline levels were low), DMPP induced very little outward transport of 3H-noradrenaline. This discrepancy indicates that DMPP has little ability to mobilize vesicularly stored 3H-amine.When the medium contained calcium (catechol-O-methyl transferase inhibited, all other mechanisms intact), 100 (but not 10) mol/l DMPP induced a hexamethonium-sensitive release of 3H-noradrenaline of short duration. Hence, in the presence of extracellular calcium, 100 mol/l DMPP elicits exocytotic release via activation of hexamethonium-sensitive nicotinic acetylcholine receptors.DMPP inhibits the monoamine oxidase of rat heart homogenate with an IC50 of about 100 mol/l.Abbreviations COMT
catechol-O-methyl transferase
- DMPP
dimethylphenylpiperazinium
- DOMA
dihydroxymandelic acid
- DOPEG
dihydroxyphenylglycol
- MAO
monoamine oxidase
- NMN
normetanephrine
- OM-fraction
column chromatographic fraction containing all O-methylated 3H-metabolites
- OMDA
fraction containing O-methylated and deaminated metabolites
Supported by the Deutsche Forschungsgemeinschaft (SFB 176)
Send offprint requests to U. Trendelenburg at the above address |
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Keywords: | Dimethylphenylpiperazinium Rat vas deferens Outward transport of noradrenaline Exocytotic release of noradrenaline Uptake1 |
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