Cardiac refractoriness in rats is reduced by angiotensin II.
We investigated the effect of angiotensin II (AII) on cardiac refractoriness in muscle trabeculae isolated from adult rat ventricle. Strength-interval curves were initially obtained under control conditions and after exposure of the muscle to Tyrode's solution containing 10(-9) M AII. AII displaced the strength-interval curves to the left. The minimal current intensity needed to elicit a propagated response was reduced by AII for all intervals used. The effect of AII was not influenced by propranolol 10(-6) M or phentolamine 10(-7) M but was blocked by 250 microM DuP 753. No change in resting potential was observed with 10(-9) M AII, but action potential duration at 50% APD50 of its amplitude was reduced by 25% and conduction velocity was appreciably decreased (41%). The effect of the peptide on APD was blocked by DuP 753. Spontaneous discharges of APs were elicited by a single stimulus in fibers exposed to 10(-9) M AII, supporting the view that AII has an arrhythmogenic action.
De Mello
W C
WC
Department of Pharmacology, School of Medicine, University of Puerto Rico, San Juan 00936-5067.
Crespo
M J
MJ
D000200:Action Potentials / Q000187:drug effects; D000804:Angiotensin II / Q000633:toxicity*; D000818:Animals; D001713:Biphenyl Compounds / Q000494:pharmacology; D004347:Drug Interactions; D004594:Electrophysiology; D006352:Heart Ventricles / Q000187:drug effects*; D007093:Imidazoles / Q000494:pharmacology; D066298:In Vitro Techniques; D019808:Losartan; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D010646:Phentolamine / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D051381:Rats; D013777:Tetrazoles / Q000494:pharmacology
D001713:Biphenyl Compounds; D007093:Imidazoles; D013777:Tetrazoles; D000804:Angiotensin II; D011433:Propranolol; D019808:Losartan; D010646:Phentolamine