Effect of agmatine on intracellular free calcium concentration in isolated rat ventricular myocytes.

The present study was to investigate the effects of agmatine (Agm) on free intracellular calcium concentration ( i) of isolated rat ventricular myocytes. i was measured by confocal microscopy in single rat ventricular myocytes which were dissociated by enzymatic dissociation method and loaded with Fluo 3-AM. The changes in i were represented by fluorescence intensity (FI) or relative fluorescence intensity (F/F 0%). The results showed that the control level of FI value of single rat ventricular myocytes was 128.8±13.8 and 119.6±13.6 in the presence of normal Tyrode′s solution containing Ca 2+ 1.0 mmol/L and Ca 2+-free Tyrode′s solution, respectively. There was no difference between these two groups (P0.05). Agm 0.1, 1, and 10 mmol/L significantly reduced the i in both extracellular solutions in a concentration-dependent manner. The similar effect of Agm on i was also observed in the presence of EGTA 3 mmol/L. KCl 60 mmol/L, PE 30 μmol/L, and Bay-K-8644 10 μmol/L, all these substances induced i elevations in ventricular myocytes. Agm (0.1, 1, and 10 mmol/L) markedly inhibited the increase in i induced by KCl, phenylephrine (PE), and Bay-K-8644. When Ca 2+ waves were produced by increasing extracellular Ca 2+ concentration from 1 to 10 mmol/L, 1 mmol/L Agm could block the propagating waves of elevated i, and reduce the velocity and duration of propagating waves. These results suggest that Agm possesses an inhibitory effects on i via blocking voltage-dependent Ca 2+ channel, and possibly by alleviating calcium release from SR in single isolated rat ventricular myocytes.