Pharmacological characterization of amine receptors on embryonic chick sensory neurones.
The effects of noradrenaline, dopamine and 5-hydroxytryptamine were investigated on the duration of the action potential of embryonic chick sensory neurones in vitro. All three amines, like gamma-aminobutyric acid, decreased the duration of the action potential evoked by current injection. The onset of the noradrenaline-induced decrease in action potential duration was fast (less than 1s) and the recovery phase was dependent upon the dose of noradrenaline applied. Rapid washout of the noradrenaline revealed a minimum 30s recovery time which was independent of the initial noradrenaline concentration. Dopamine and 5-hydroxytryptamine could mimic the effects of noradrenaline on action potential duration. The ED50 for all three amines was approximately 1 microM. At a saturating concentration of 10 microM, noradrenaline was more potent than dopamine and 5-hydroxytryptamine. Saturating doses of noradrenaline and dopamine or 5-hydroxytryptamine were not additive. Responses to all three amines were affected similarly by antagonists: they were antagonized by yohimbine, phentolamine, haloperidol and mianserin but not by propranolol, prazosin, domperidone, spiperone or methysergide. Clonidine and xylazine (alpha 2-adrenoceptor agonists) were also without effect. In contrast to the amines, saturating concentrations of gamma-aminobutyric acid were additive with those of noradrenaline. Responses to GABA were not antagonized by the amine receptor antagonists. The evidence described here suggests that the amines and gamma-aminobutyric acid acid decrease sensory neurone action potential duration via pharmacologically-distinct membrane receptors. In addition, it is likely that the amines are acting via a single class of receptor whose pharmacology is different from classical adrenoceptors, dopamine receptors and 5-hydroxytryptamine receptors.
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002642:Chick Embryo; D004298:Dopamine / Q000494:pharmacology; D018492:Dopamine Antagonists; D009475:Neurons, Afferent / Q000502:physiology*; D018377:Neurotransmitter Agents / Q000494:pharmacology*; D009638:Norepinephrine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D011941:Receptors, Adrenergic / Q000502:physiology*; D011956:Receptors, Cell Surface / Q000502:physiology*; D011963:Receptors, GABA-A; D012701:Serotonin / Q000494:pharmacology; D012702:Serotonin Antagonists / Q000494:pharmacology; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
D018492:Dopamine Antagonists; D018377:Neurotransmitter Agents; D011941:Receptors, Adrenergic; D011956:Receptors, Cell Surface; D011963:Receptors, GABA-A; D012702:Serotonin Antagonists; D012701:Serotonin; D005680:gamma-Aminobutyric Acid; D004298:Dopamine; D009638:Norepinephrine