[Electrophysiological effects of agmatine on guinea pig papillary muscles in vitro]

The cardiac electrophysiological effects of agmatine (AGM) were examined in guinea pig papillary muscle using intracellular microelectrode technique. The results obtained are as follows. (1) Duration of action potential (APD) in normal papillary muscles were decreased by AGM in a concentration-dependent manner. (2) In partially depolarized papillary muscles, amplitute of action potential, overshoot, maximal velocity of phase 0 depolarization and APD were depressed by AGM. (3) Pretreatment with NG-nitro-L-arginine methyl ester (L-NAME, 0.5 mmol/L) did not affect the above effects of AGM (1 mmol/L) on papillary muscles. (4) The effects of AGM (1 mmol/L) could be blocked completely by pretreatment with idazoxan (0.1 mmol/L), an alpha 2-adrenoceptor (alpha 2-AR) and imidazoline receptor (IR) antagonist. All these results indicate that the effects of AGM on papillary muscles are likely due to a decrease of intracellular calcium mediated by alpha 2-AR and IR.