Effect of urapidil on the action potentials in the guinea-pig ventricular myocardium.
The electrophysiological effects of urapidil, a new alpha 1-adrenoceptor antagonist, were assessed in the reserpinized guinea-pig ventricular myocardium. Urapidil suppressed the maximal rate of rise (Vmax) of steady-state action potentials elicited by the fast responses at high concentrations independently of blockade of myocardial alpha-adrenoceptors, but not the Vmax of Ca(2+)-dependent slow action potentials of partially depolarized muscles in concentrations tested (up to 1.1 mM). Urapidil at high concentrations prolonged the action potential durations of the fast and slow responses in a manner similar to the quinidine-like antiarrhythmic drugs. These results suggest that the inhibitory effect of urapidil on the slow inward Ca2+ current and the Na+ current is in practice negligible.
Department of Internal Medicine, Tottori University School of Medicine, Yonago, Japan.
N
N
Noguchi
J
J
Hasegawa
H
H
Omodani
T
T
Nawada
S
S
Matsuoka
I
I
Hisatome
H
H
Kotake
H
H
Mashiba
D000200:Action Potentials / Q000187:drug effects; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000494:pharmacology / Q000502:physiology; D006168:Guinea Pigs; D006321:Heart / Q000187:drug effects* / Q000502:physiology; D006352:Heart Ventricles / Q000187:drug effects; D066298:In Vitro Techniques; D007552:Isotonic Solutions; D010879:Piperazines / Q000494:pharmacology*; D011188:Potassium / Q000494:pharmacology; D016276:Ventricular Function
D000317:Adrenergic alpha-Antagonists; D007552:Isotonic Solutions; D010879:Piperazines; C037692:Tyrode's solution; C015568:urapidil; D011188:Potassium; D002118:Calcium