Inhibition of cytosolic Ca++ mobilization in human platelets by the antianginal drug trapidil and its derivative AR 12463.

The antianginal drug trapidil (5-methyl-7-diethylamino-s-triazolo-(1.5-a)pyrimidine) and its derivative AR 12463 (5-piperidino-7-(N-(n-amyl)-N-(beta-hydroxyethyl)-amino)-s-triazolo(1.5- a) pyrimidine) inhibit the thromboxane A2 agonist (U-46619)-induced mobilization of intracellular platelet-free Ca++ as measured with the fluorescent Ca++ indicator Indo-1. This inhibitory effect is independent of extracellular Ca++ concentration, and AR 12463 is about 70-fold more active than trapidil itself.