Hyperpolarizing responses of single mammalian sympathetic neurones to acetylcholine and to dopamine.
Acetylcholine (ACh) applied iontophoretically can elicit not only nicotinic fast (f-) and/or muscarinic slow (s-) depolarizations (DP) but also hyperpolarizing responses (HP), all in the same cell. HPs were either 'initial' (sharp onset at the end of ACh delivery) or 'secondary' (variable later onsets). Pretreatment with bretylium eliminated secondary, but not initial, responses to ACh. Pretreatment with both BCh and bretylium eliminated essentially all HP responses to ACh, with good DP responses remaining. Test responses to the more purely muscarinic agent BCh exhibited only a smooth, large s-DP with no secondary HP components, even in ganglia not pretreated with bretylium. The foregoing evidence is explainable by our previous proposals that ACh can elicit two types of HPs, one mediated by muscarinic receptors (putatively located on DA interneurones) and another by non-muscarinic receptors (putatively releasing norepinephrine at dendro-dendritic junctions). Dopamine (DA) applied iontophoretically could also elicit HP responses from the same cells. Iontophoretic DA could elicit an HP at any depth (up to 290 micron tested) in the ganglion. However, bulk application of DA (in the extra-ganglionic medium) was only effective on neurones impaled in the outer 30 micron. This may help explain the variable findings with applied DA.
D000109:Acetylcholine / Q000494:pharmacology*; D000320:Adrenergic Fibers / Q000187:drug effects* / Q000502:physiology; D000818:Animals; D018723:Bethanechol; D001626:Bethanechol Compounds / Q000494:pharmacology; D001949:Bretylium Compounds / Q000494:pharmacology; D004298:Dopamine / Q000494:pharmacology*; D005728:Ganglia, Sympathetic / Q000187:drug effects* / Q000502:physiology; D007478:Iontophoresis; D008564:Membrane Potentials / Q000187:drug effects*; D009433:Neural Inhibition; D011817:Rabbits
D001626:Bethanechol Compounds; D001949:Bretylium Compounds; D018723:Bethanechol; D000109:Acetylcholine; C045166:bretylium; D004298:Dopamine