In vitro PAI-1 can be reactivated by denaturants such as SDS, guanidine HCl, and urea, and it has also been suggested that negatively charged phospholipids exposed on the surface of activated platelets could reactivate PAI-1. On the other hand, it has been reported that SDS may cause dissociation of the tPA-PAI-1 complex. To rule out the possibility that our results were due to reactivation and/or dissociation of the tPA-PAI-1 934660-93-2 complex formed, we performed a series of experiments both with and without SDS in the loading buffer 935693-62-2 before electrophoresis. However, these studies showed no detectable differences in PAI-1 activity whether SDS was present or not. This is in agreement with a previous study reporting that the SDS-activatable form of PAI-1 might not be present in human platelets. How, then, could the activity of PAI-1 be preserved for such a prolonged period of time in the platelet? A potential mechanism has been suggested by Lang and Schleef, who showed that platelets possess a unique mechanism for stabilization of active PAI-1, by packaging together with other large a-granule proteins in a calcium-dependent manner. Active PAI-1 in plasma is stabilized by binding to vitronectin which has also been detected in platelet a-granules. However, some studies have failed to detect the vitronectin-PAI-1 complex in platelets and it is therefore controversial whether vitronectin is the stabilizing factor of PAI-1 in platelets. This issue remains to be evaluated. From a clinical perspective, there is compelling evidence that platelet-derived PAI-1 has an important physiologic and pathophysiologic role in making platelet-rich blood clots resistant to both endogenous and pharmacological thrombolysis. Despite this, most previous studies have reported activity levels of platelet PAI-1 that are probably far too low to explain its putative functional role. Our results may provide the missing clue to reconcile the seemingly contradictory findings. Taken together, our observations suggest that the large amount of PAI-1 stored in platelets is functional and thus capable to inhibit fibrinolysis, which may explain their observed role in clot stabilization. The present findings suggest that pre-analytic preparatory procedures have contributed to the underestimation of platelet PAI-1 activity in previous studies. Whole genome expression measurements provide snapshots of the abundance of thousands of transcripts and have the potential to paint a comprehensive picture of modulated biological processes in a given sample. While most problems relating to the statistically robust estimation of transcript levels changing between different samples have been successfully solved, the task of manually interpreting t
