Effects of SR 44866, a Potassium Channel Opener, on Action Potentials of Rabbit, Guinea Pig, and Human Heart Fibers

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Abstract
Summary: The effects of various concentrations (3 x 10-8–1 x 10-5M) of SR 44866, a K+ channel opener, on action potential (AP) characteristics were investigated in isolated rabbit sinoatrial node (SAN), rabbit Purkinje fibers, guinea pig ventricle, human atrium, and human papillary muscle. SR 44866 (up to 1 x 10 SM), like cromakalim and pinacidil, did not modify SAN AP and automaticity of the rabbit heart. In atrial, Purkinje and ventricular fibers of animal and human hearts, SR 44866 did not significantly change membrane resting potential, AP amplitude, or maximum rate of phase 0 (dV/dtmax). The main AP modifications induced by SR 44866 were concentration-dependent reductions in plateau amplitude and AP duration (APD): IC50 2 x 107, 7 x 107, 1.4 x 10-6, 2.5 x 10 6, and >10 5M for human atrium, human ventricle, guinea pig ventricle, rabbit Purkinje, and rabbit atrium, respectively. In isolated guinea pig heart, SR 44866 induced decreases in contractions (IC50 1.7 x 10 6M) and coronary perfusion pressure (CPP) (ICs50 2.1 x 10-8M) with a very slight reduction (5% at 1 x 10 6M) in spontaneous heart rate (HR). Negative inotropic effect (guinea pig) and APD shortenings (guinea pigs and humans) of SR 44866 (1 x 10-6 and 3.10 6M) were antagonizedbyglibenclamide(3 x 10-7 to 3 x 10 6M), a specific blocker of cardiac KATP, channels. The data support the hypothesis that SR 44866 activates ATP-sensitive K+ channels, which are present in the atria and ventricles of the human heart but not in pacemaker cells of rabbit SAN.

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