Effects of agmatine on afterdepolarizations induced by isoproterenol in guinea pig papillary muscles.
Abstract
AIM:
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.
CONCLUSION:
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.
Keywords:
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.
CONCLUSION:
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.