The platelet release reaction is analogous to the process of exocytosis by which many other secretory cells release hormones or mediators from intracellular granules. Anion transport blocking (ATB) drugs Inhibit release of epinephrine from isolated chromaffin granules (CG) by blocking chloride uptake and preventing osmotic lysis. Studies on platelets analagous to those done on CG showed that increasing osmotic strength in the range 600-1000 m0sm progressively suppressed serotonin release to completion and that ATB drugs (viz, probenecid, SITS, pyridoxal phosphate and suramin) at mM concentrations completely inhibited release and aggregation of human platelets stimulated by thrombin, ADP, A23187, epinephrine or collagen. Sulfinpyrazone has the appropriate structure for anionic blocking, and may suppress platelet function as effectively by this mechanism as by cycloxy-genase inhibition. The ATB drugs acted apparently to prevent movement of OH- from the more alkaline medium into the relatively acidic granule, for platelet release was not inhibited by replacing anions with isethionate or sucrose, but was markedly dependent on OH- in the pH range 6 to 7.5 where inhibition by the ATB drugs was competitive with respect to OH-. Since the ATB compounds include some relatively nontoxic drugs in common use, and since their action on platelets differs markedly from that of aspirin, they should receive attention as potential alternative or auxiliary antithrombotic agents.
Halide-selective, proton-coupled anion transport by phenylthiosemicarbazones
