ISSN:
1432-2013
Keywords:
Cardiac electrophysiology
;
Ion channels
;
Chloride channels
;
Action potentials
;
Patch clamp
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Abstract Modulation of the ventricular action potential by β-adrenergic activation of Ca2+, K+ and cyclic adenosine monophosphate (cAMP)-dependent Cl− channels was assessed in enzymatically isolated guinea-pig ventricular myocytes. The effectiveness and relative selectivity of 9-anthracene carboxylic acid (9-AC), as an antagonist of cAMP-dependent Cl− channels was also tested. Membrane currents and action potentials were recorded using the conventional whole-cell variant of the patch-clamp technique or with the amphotericin B perforated-patch technique. The β-adrenergic agonist isoproterenol either increased or decreased action potential duration depending on whether the dominant effect was on inward Ca2+ currents or on outward K+ or Cl− currents. When Ca2+ and K+ channel modulation was prevented by nisoldipine and low temperature respectively, β-adrenergic activation of Cl− channels caused a significant reduction in action potential duration and a slight depolarization of the membrane potential. The β-adrenergic-mediated effects were reversed by the Cl− channel blocker, 9-AC. In the absence of β-adrenergic stimulation, 9-AC had no detectable effects on action potentials or Ca2+ currents. These results suggest that β-adrenergic activation of Cl− channels is a potent mechanism for regulation of action potential duration and that 9-AC may be a useful, relatively specific, pharmacological tool for evaluating the physiological role of cAMP-activated Cl− channels in heart. 9-AC also reversed the ability of isoproterenol to antagonize prolongation of action potential duration by the class III antiarrhythmic agent E-4031.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00375102
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