Effects of H1-receptor blocking drugs on the frog sartorius neuromuscular junction.
The effects of H1-receptor blocking agents, pyrilamine, promethazine, and diphenhydramine, on the amplitude and time course of endplate potentials (e.p.ps) were studied in the sartorius muscles of frogs. H1-receptor blockers (10(-5)-10(-4) M) reduced the amplitude of e.p.ps recorded intracellularly without affecting the resting membrane potential. The acetylcholine potential was decreased by perfusion of H1-receptor blockers. However, when the muscle fibre was stimulated directly, threshold and magnitude of action potential were not affected by H1-receptor blockers. The time constant of decay of the e.p.ps recorded extracellularly was reduced by H1-receptor blockers and the decay remained exponential with a single time constant. The quantal content was not reduced by perfusion of H1-receptor blockers at a concentration of 10(-4) M. It is assumed that the major site of action of these H1-receptor blocking agents is at the postsynaptic membrane.
D000200:Action Potentials / Q000187:drug effects; D000631:Aminopyridines / Q000494:pharmacology*; D000818:Animals; D004155:Diphenhydramine / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004553:Electric Conductivity; D004594:Electrophysiology; D008564:Membrane Potentials / Q000187:drug effects; D009469:Neuromuscular Junction / Q000187:drug effects*; D010477:Perfusion; D011398:Promethazine / Q000494:pharmacology*; D011738:Pyrilamine / Q000494:pharmacology*; D011898:Ranidae; D011968:Receptors, Histamine / Q000378:metabolism*; D011969:Receptors, Histamine H1 / Q000378:metabolism*; D013997:Time Factors
D000631:Aminopyridines; D011968:Receptors, Histamine; D011969:Receptors, Histamine H1; D004155:Diphenhydramine; D011398:Promethazine; D011738:Pyrilamine