Negative chronotropic effect of a novel class III antiarrhythmic drug, UK-68,798, devoid of beta-blocking action on isolated guinea-pig atria.
1. The chronotropic effects of a novel class III antiarrhythmic drug, UK-68,798, and the beta-adrenoceptor blocker, propranolol, for comparison, were studied on spontaneously beating right atria isolated from guinea-pigs in the absence and presence of increasing concentrations of isoprenaline (10(-10)-10(-4) M). 2. UK-68,798 (10(-9)-10(-5) M) decreased spontaneous atrial rate by 6-21%. Propranolol (10(-8) -10(-6) M) also had a negative but significantly smaller chronotropic effect. 3. UK-68,798 dose-dependently reduced the maximal positive chronotropic effect induced by isoprenaline, but without significantly shifting the concentration-response curve for isoprenaline in a parallel fashion. A pD'2 value of 5.88 was obtained. As expected, propranolol displayed a competitive inhibition with a pA2 value of 8.21. 4. The results demonstrate a negative chronotropic effect of UK-68,798, which is not associated with a beta-adrenoceptor blocking action. We suggest that the negative chronotropic effect is linked with potassium channel blockade and thereby the class III antiarrhythmic action of UK-68,798.
Department of Medical Physiology, University of Tromsø, Norway.
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D000319:Adrenergic beta-Antagonists; D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology*; D003864:Depression, Chemical; D005260:Female; D006168:Guinea Pigs; D006325:Heart Atria / Q000187:drug effects; D006339:Heart Rate / Q000187:drug effects*; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D010627:Phenethylamines / Q000494:pharmacology*; D011433:Propranolol / Q000494:pharmacology; D012849:Sinoatrial Node / Q000187:drug effects; D013449:Sulfonamides / Q000494:pharmacology*
D000319:Adrenergic beta-Antagonists; D000889:Anti-Arrhythmia Agents; D010627:Phenethylamines; D013449:Sulfonamides; D011433:Propranolol; D007545:Isoproterenol; C063533:dofetilide