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Analysis of the hyperpolarizing effect of catecholamines on canine cardiac Purkinje fibres
Author(s) -
Neto Francisco Riccioppo,
Sperelakis Nicholas
Publication year - 1989
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.1476-5381.1989.tb11857.x
Subject(s) - hyperpolarization (physics) , isoprenaline , chemistry , ouabain , purkinje fibers , depolarization , membrane potential , tetrodotoxin , biophysics , medicine , potassium , acetylcholine , extracellular , endocrinology , sodium , electrophysiology , stimulation , biochemistry , biology , stereochemistry , organic chemistry , nuclear magnetic resonance spectroscopy
1 The hyperpolarization induced by catecholamines on barium‐depolarized (0.2–0.8 m m BaCl) canine cardiac Purkinje fibres, in vitro , was studied by use of conventional microelectrode recordings of transmembrane electrical potentials. 2 Noradrenaline, adrenaline and isoprenaline hyperpolarized Purkinje fibres in a concentration‐dependent manner from a threshold concentration around 5 n m . The three catecholamines were shown to be approximately equipotent. Tachyphylaxis was observed when the interval between catecholamine applications was less than 15 min. 3 Atenolol (10 μ m ) blocked the hyperpolarization reversibly and theophylline (0.5 m m ) potentiated it. 4 Tetrodotoxin (5 μ m ) did not affect the hyperpolarization induced by isoprenaline. Acetylcholine and histamine, up to 10 μ m , were not effective in hyperpolarizing Purkinje fibres. 5 Low extracellular potassium concentrations (zero and 1 m m ) did not affect the hyperpolarization, but high extracellular potassium concentrations (10–20 m m ), markedly reduced the effect of isoprenaline (100 n m ). 6 Reduction of the extracellular sodium concentration produced a roughly proportional reduction in the isoprenaline‐induced hyperpolarization. The hyperpolarization was reversibly blocked in 34 m m sodium Tris‐Tyrode solution. 7 The hyperpolarization was not reduced in Tyrode solution containing 0.6 m m calcium, but was drastically reduced in zero‐calcium Tyrode solution. This effect was reversible. 8 Addition of verapamil (5–10 μ m ) diminished the hyperpolarization, in a concentration‐dependent manner. This effect was partially reversed after washing. 9 Ouabain (0.7–1 μ m ) significantly reduced the isoprenaline‐induced hyperpolarization, but 2,4‐dinitrophenol (0.2 m m ) did not affect it. 10 Caesium chloride (20 m m ) abolished the hyperpolarization. The blockade was only partially reversed upon washing. 11 It is suggested that the hyperpolarization induced by a short exposure to catecholamines is mainly due to an increase in potassium permeability (P K ). A mechanism involving calcium‐dependent potassium channels might underlie the increase in P K .