Abstract: AIM: To observe the effects of berberine (Ber) on left atria and trachea in guinea pigs. METHODS: The experiment was carried out with isolated left atria and trachea in guinea pigs, and the effects and in-teractions were compared between Ber and pinacidil (Pin). RESULTS: Ber concentration-dependent in-creased the force of contractile, while Pin decreased the force. Ber leaded a parallel rightward shift in accumulated response curve of depression contraction of left atria by Car, and it hardly changed the maximum response (E max), while Pin leaded a parallel leftward shift in the same curve.In the combination of Ber and Pin, the dose-response curve hardly changed as the control one. In iso-lated guinea pig trachea, Ber caused a leftward shift in the dose-response curve of ACh, whereas Pin produced a rightward shift in the same curve without changing E max. When both Ber and Pin existed in the same container, there was no modification in the response to ACh.CONCLUSION: Ber shows the effect of blocking potassium channel.

Key words: berberine, pinacidil, left atria, tra-chea, dose-response curve