title: The effect of harmaline on membrane potentials of rat atrial contractile fibers.
abstract: Rat atria either beating spontaneously or electrically driven were were perfused in vitro at 30 degrees C. When the preparations were exposed to harmaline 8.3 x 10(-5) or 16.6 x 10(-5) M the atrial rate showed down and the following changes in membrane potentials were observed: (1) a transient increase in the amplitude of the action potential (AAP), in the absence of any change in the magnitude of the resting potential (RP), followed by a progressive decrease of AaP; (2) a progressive decline of the slope of the fast ascending phase of the action potential, which was initially independent of any change in the magnitude of the rp; (3) a progressive increase of the duration of the action potential; (4) a fall in the magnitude of the resting potential. The conclusions proposed are that harmaline: (1) stimulates the slow current responsible for the last part of the upstroke and the beginning of the repolarization; (2) inhibits the sodium current responsible for the fast component of the upstroke; (3) slows doen the processes responsible for the repolarization; (4) inhibits the (Na+-K+) activated membrane ATPase.
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000251:Adenosine Triphosphatases / Q000037:antagonists & inhibitors; D000470:Alkaloids / Q000494:pharmacology*; D000818:Animals; D016275:Atrial Function; D006246:Harmaline / Q000494:pharmacology*; D006325:Heart Atria / Q000201:enzymology; D006339:Heart Rate / Q000187:drug effects; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects*; D009474:Neurons / Q000502:physiology*; D009638:Norepinephrine / Q000494:pharmacology; D011188:Potassium; D051381:Rats; D012964:Sodium
chemical_list: D000470:Alkaloids; D012964:Sodium; D006246:Harmaline; D000251:Adenosine Triphosphatases; D011188:Potassium; D009638:Norepinephrine