Effects of 3,6-dimethamidodibenzopyriodonium citrate (Ⅰ-65) on contractions of rat aortic strips and cat papillary muscles

I-65 is a new compound synthesized in China in 1984. The contractions induced by KCk, CaCl2, NE, AT11, or pituitrin in rat aortic strips were inhibited by Ⅰ-65 1 μmol/L. Their concentration-response curves were in the same manner of noncompetitive antagonism and the pD’2 values were practically the same. Ⅰ-65 inhibited the slow Ca0 dependent component (slow phase) of contraction evoked by NE in rat aortic strips and had weaker effect on the fast non-sustained component (fast phase). This kind of action was similar to that of verapamil. The inhibition of contraction of rat aortic strips was more pronounced when Ⅰ-65 was added into the bath before the experiment of depolarization by KCl than after it. This result indicated that Ca0 influx was the main step blocked by Ⅰ-65 which showed a potentiated inhibition in combination with verapamil. Ⅰ-65 caused an excitation-contraction uncoupling in cat papillary muscles. Ⅰ-65 was believed to be a calcium channel blocker.