Abstract: AIM: To study the effects of xanthotoxol (XT) on physiological characteristics and its mechanism in isolated guinea pig atria. METHODS: It was determined by the contractile amplitude, excitability and the spontaneous beats in the right atria, respectively. RESULTS: In the experiment of contractile amplitude, after 15 min of administration of XT 20, 40 and 80 μmol·L^-1, the contractile force of left atria was 0.85, 0.68, and 0.48 g, respectively (P <0.05, compared with control group).It showed that XT could decrease the contractile force in concentration-dependent manner significantly.In the experiment of the sinus rates, after 30 min of administration of XT 20 and 40 μmol·L^-1, the fact that the sinus rates decreased from 90.0 min-1 to 60.2 min-1 and 38.7 min-1, respectively (P <0.05 vs solvent group) indicated that XT significantly reduced the sinus rates.In the experiments of the functional refractory period and excitability, no effects of XT were demonstrated. CONCLUSION: XT can decrease the contractile force and the spontaneous beats.The inotropic and chronotropic action of XT may be related to inhibiting Ca²⁺ influx from outside the cells and Ca 2+ release from calcium reservoir inside the cells.

Key words: xanthotoxol, coumarin, guinea pig auricle, functional refractory period, contractility