Platelet membrane fluidity and intraplatelet Ca2+ homeostasis are affected in uremia

Recently we have described a dependence of platelet disability in thrombosis upon the progression in renal failure and an elevated level of RGDS-containing degradation products in uremic plasma, which is also correlated with progression in renal failure. Based on fluorescence techniques, our present investigations concerned possible changes in platelet membrane fluidity and intraplatelet calcium homeostasis in uremic platelets. Washed platelets loaded with DPH or with Fura-2 were examined with LS-50 luminescence spectrometer. Light anisotropy of DPH measured at 37 degrees C was significantly higher in control platelet membranes than in uremic ones. It can be considered as more fluidic membranes of uremic platelets. No difference between the basal intraplatelet calcium level was found for uremic and control platelets, but in the presence of 5 mM EGTA, the basal level was reduced significantly deeper in uremic platelets. Activation of platelets by both ADP (12.5 microM) and thrombin (0.1 U/ml) resulted in rapid increase in the intraplatelet calcium level in the examined platelets, but this increase was significantly higher for control platelets. The results indicate an abnormal intracellular calcium homeostasis in uremic platelets, which is associated with an increased fluidity of platelet membranes in uremia.