Effects of 4-aminopyridine on the non-adrenergic inhibitory neurotransmission in the guinea-pig duodenum.
The effects of 4-aminopyridine (4-AP) on the non-adrenergic inhibitory potential (i.p.) in the longitudinal and circular smooth muscle cells of the guinea-pig duodenum were investigated using intracellular microelectrodes. The membrane potential of both smooth muscles was decreased by 4-AP and the amplitude of the evoked i.p.s. was increased. In a low-calcium solution (0.25 mM), the amplitude of the i.p.s. was reduced but the additional application of 4-AP increased the amplitude. In the 4-AP containing low-calcium solution, the i.p. was inhibited by verapamil and EGTA. The inhibitory effect of verapamil on the i.p. evoked in a low-calcium solution was less in the presence of 4-AP than that in its absence. In a high-calcium solution (5 mM), the amplitude of the i.p. increased and the additional application of 4-AP enhanced the i.p. further. The amplitude of the i.p. elicited in high-potassium solutions was not changed by 4-AP. The i.p. was not potentiated by 2-aminopyridine or 2,5-diaminopyridine. Tetraethylammonium ions enhanced the amplitude of the i.p. at low concentration but decreased it in high concentration. In a few longitudinal smooth muscle cells, the evoked excitatory potential (e.p.) was observed. Potentiation of the e.p. by 4-AP was completely blocked by atropine. From the results obtained, it is suggested that the release of the non-adrenergic inhibitory neurotransmitter is increased by 4-AP due to increase calcium influx in the nerve terminals. The release of the cholinergic excitatory neurotransmitter seems to be increased by 4-AP.
D015761:4-Aminopyridine; D000631:Aminopyridines / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D000697:Central Nervous System Stimulants / Q000494:pharmacology*; D004386:Duodenum / Q000294:innervation; D004533:Egtazic Acid / Q000494:pharmacology; D005071:Evoked Potentials / Q000187:drug effects; D005260:Female; D006168:Guinea Pigs; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects* / Q000502:physiology; D009433:Neural Inhibition / Q000187:drug effects; D009435:Synaptic Transmission / Q000187:drug effects*; D013757:Tetraethylammonium Compounds / Q000494:pharmacology; D014700:Verapamil / Q000494:pharmacology
D000631:Aminopyridines; D000697:Central Nervous System Stimulants; D013757:Tetraethylammonium Compounds; D004533:Egtazic Acid; D015761:4-Aminopyridine; D014700:Verapamil; D002118:Calcium