Actions of 4-aminopyridine on mammalian ganglion cells.
The effects of 4-aminopyridine (4-AP) on membrane electrical properties and synaptic transmission in neurons of the isolated rabbit superior cervical ganglion were investigated. 4-AP (0.03-0.1 mM) increased the amplitude of the fast excitatory postsynaptic potential (f-EPSP) without affecting appreciably either the acetylcholine (ACh) depolarization induced by iontophoresis of ACh or the passive and active membrane properties of the neurons. At concentrations of 1-5 mM, 4-AP reversibly depressed the amplitude of the f-EPSP as well as the ACh depolarization; a slight to moderate prolongation of the action potential duration was observed. In addition to the effects on evoked synaptic potentials, 4-AP induced spontaneous discharges which were abolished reversibly by curare, low Ca solution or Co. The results indicate that 4-AP at low concentrations facilitated evoked as well as spontaneous release of ACh by a presynaptic mechanism, whereas at higher concentrations it exerted a curare-like effect on the postsynaptic membrane.
D015761:4-Aminopyridine; D000631:Aminopyridines / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D005728:Ganglia, Sympathetic / Q000187:drug effects*; D018738:Hexamethonium; D006584:Hexamethonium Compounds / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects*; D011817:Rabbits; D009435:Synaptic Transmission / Q000187:drug effects*; D014403:Tubocurarine / Q000494:pharmacology
D000631:Aminopyridines; D006584:Hexamethonium Compounds; D018738:Hexamethonium; D015761:4-Aminopyridine; D002118:Calcium; D014403:Tubocurarine