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Electrophysiological effects of labetalol on canine atrial, cardiac Purkinje fibres and ventricular muscle
Author(s) -
Mill Jose Geraldo,
Neto Francisco Riccioppo
Publication year - 1987
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1987.tb11365.x
Subject(s) - labetalol , purkinje fibers , electrophysiology , membrane potential , chemistry , effective refractory period , depolarization , cardiac muscle , anesthesia , medicine , blood pressure , biochemistry
1 Using conventional microelectrode techniques for the intracellular recordings of the membrane potential, the effects of labetalol were studied on cardiac Purkinje, atrial and ventricular muscle fibres of the dog. 2 Labetalol (1–10 μ m ) reduced, in a concentration‐dependent manner, the action potential amplitude (APA) and the maximum rate of rise of the action potential ( V max ) in Purkinje fibres. 3 The action potential duration (APD) was decreased in Purkinje fibres but significantly increased in ventricular fibres after small concentrations of labetalol (1–3 μ m ). The atrial fibres were not very sensitive to labetalol. 4 Depolarization of the cardiac Purkinje fibres by increasing the external potassium concentration (8–12 m m ), potentiated the labetalol effects on APA and V max but blocked its effects on the APD. 5 The effects of labetalol on V max of Purkinje fibres were dependent on the frequency of stimulation. 6 The ratio of the effective refractory period to the APD was increased both in normally polarized and depolarized Purkinje fibres after treatment with labetalol (10 μ m ). 7 Labetalol (10 μ m ) shifted the membrane responsiveness curve of Purkinje fibres by about 10 mV in the hyperpolarizing direction. 8 The slow response obtained in K‐depolarized, Ba‐treated Purkinje fibres was not significantly affected by labetalol (10–100 μ m ). 9 It is suggested that labetalol can exert Class I and Class III antiarrhythmic actions in cardiac muscle of the dog in vitro.