title: Frequency dependence of the effect of harmine on the duration of the action potential of guinea pig atrial muscle.
abstract: The effect of harmine on the duration of the action potential (APD) of guinea pig atrial muscle is analyzed. Harmine prolongs APD through both a depressant effect on automaticity and a direct effect on atrial repolarization. In atria driven at a constant rate: (a) the direct effect becomes less with a faster drive; (b) an increase in concentration of harmine does not result in a greater prolongation of APD. Increased extracellular Ca2+ concentration annulles the APD-prolonging effect.
mesh_terms: D000200:Action Potentials / Q000187:drug effects*; D000470:Alkaloids / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000502:physiology; D003864:Depression, Chemical; D004305:Dose-Response Relationship, Drug; D006168:Guinea Pigs; D006247:Harmine / Q000494:pharmacology*; D006321:Heart / Q000502:physiology*; D006325:Heart Atria / Q000187:drug effects; D006339:Heart Rate / Q000187:drug effects; D066298:In Vitro Techniques; D013997:Time Factors
chemical_list: D000470:Alkaloids; D006247:Harmine; D002118:Calcium