[Calcium antagonistic effect of Xanthotoxol on isolated guinea pig atria].

Objective: To study the mechanism of depressant effect of xanthotoxol (XT) on contractility in the isolated guinea pig atria.

Methods: The contractile force of the isolated left atria was determined by tension recording method.

Results: In the experiments on contractility of the left atria XT and Verapamil (Ver) significantly depressed the positive staircase phenomena, which was reversed by Ver but not by XT. However, the post-rest potentiation of myocardial contraction in the left atria was only markedly decreased by XT but not by Ver. Furthermore, XT not only attenuated the positive inotropic action, but also delayed the following toxicity response induced by ouabain in the isolated left atria.

Conclusion: XT blocked not only the voltage dependent calcium channel, but also the receptor operated calcium channel in the isolated guinea pig atria.