Effects of agmatine on afterdepolarizations induced by isoproterenol in guinea pig papillary muscles.
OBJECTIVE
To study the effects of agmatine (Agm) on early afterdepolarizations (EAD) and delayed afterdepolarizations (DAD) induced by isoproterenol (Iso) in guinea pig papillary muscles.


METHODS
EAD and DAD were recorded using intracellular glass microelectrode technique.


RESULTS
(1) EAD and DAD induced by Iso 20 nmol.L-1 were markedly inhibited by pretreatment with Agm 1.0-2.0 mmol.L-1 in a concentration-dependent manner. (2) NG-nitro-L-arginine methyl ester (L-NAME, 0.5 mmol.L-1), a NOS inhibitor, did not affect the inhibitory effects of Agm (1.0 mmol.L-1) on EAD and DAD induced by Iso. (3) The inhibitory effects of Agm (1.0 mmol.L-1) on EAD and DAD induced by Iso (20 nmol.L-1) were eliminated by pretreatment with idazoxan (Ida, 0.1 mmol.L-1), an alpha-2 adrenergic receptor (alpha 2-AR) and imidazoline receptor (IR) antagonist.


CONCLUSIONS
The inhibitory effects of Agm on EAD and DAD induced by Iso in papillary muscles is related to the reduction in calcium influx and mediated by alpha 2-AR and/or IR.
Department of Physiology, Institute of Basic Medicine, Hebei Medical University, Shijiazhuang 050017, China.
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D058647:Adrenergic alpha-2 Receptor Agonists; D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000376:Agmatine / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D004594:Electrophysiology; D005260:Female; D006168:Guinea Pigs; D007093:Imidazoles / Q000494:pharmacology; D054755:Imidazoline Receptors; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D010210:Papillary Muscles / Q000502:physiology*; D011955:Receptors, Drug / Q000819:agonists
D058647:Adrenergic alpha-2 Receptor Agonists; D000318:Adrenergic beta-Agonists; D007093:Imidazoles; D054755:Imidazoline Receptors; D011955:Receptors, Drug; D000376:Agmatine; D007545:Isoproterenol; D002118:Calcium