Electrophysiological effects of agmatine on human atrial fibers.
The objective of the present study was to study the electrophysiological effects of agmatine on human atrial fibers obtained at cardiac surgery using standard microelectrode techniques. Agmatine (1 to approximately 10 mM) decreased the action potential amplitude (APA), maximum upstroke velocity of phase 0 depolarization (Vmax), velocity of diastolic (phase 4) depolarization (VDD), rate of pacemaker firing (RPF), and action potential duration at 50 and 90% of repolarization (APD(50-90)) in a concentration-dependent manner. Pretreatment with N(G)-nitro-L-arginine methyl ester (L-NAME, 0.5 mM), a NOS inhibitor, did not affect the electrophysiological effects of agmatine (5 mM) on human atrial fibers. The effects of agmatine (5 mM) could be blocked completely by pretreatment with idazoxan (0.1 mM), an alpha-2 adrenergic receptor (alpha2-AR) and imidazoline receptor (IR) antagonist. All these results indicate that the effects of agmatine on human atrial fibers are likely due to a decrease of intracellular calcium mediated by IR and/or alpha2-AR.
Li
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XT
Department of Physiology, Hebei Medical University, Shijiazhuang, China.
He
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Liu
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Liu
L L
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Zhang
W L
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Zhao
H
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Duan
H R
HR
D000200:Action Potentials / Q000187:drug effects; D000293:Adolescent; D058669:Adrenergic alpha-2 Receptor Antagonists; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000376:Agmatine / Q000494:pharmacology*; D020517:Atrial Appendage / Q000502:physiology*; D002648:Child; D002675:Child, Preschool; D004594:Electrophysiology; D006330:Heart Defects, Congenital / Q000601:surgery; D006801:Humans; D019329:Idazoxan / Q000494:pharmacology; D054755:Imidazoline Receptors; D066298:In Vitro Techniques; D007223:Infant; D009200:Myocardial Contraction / Q000502:physiology*; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D011955:Receptors, Drug / Q000037:antagonists & inhibitors
D058669:Adrenergic alpha-2 Receptor Antagonists; D000317:Adrenergic alpha-Antagonists; D054755:Imidazoline Receptors; D011955:Receptors, Drug; D000376:Agmatine; D019331:NG-Nitroarginine Methyl Ester; D019329:Idazoxan