PLATELET MEMBRANE FLUIDITY AND INTRAPLATELET CA2+ MOBILIZATION ARE AFFECTED IN UREMIA

In present investigations, platelet membrane fluidity and intraplatele t Ca2+ mobilization were analysed in uraemic platelets by fluorescence techniques. Thirteen non-dialyzed uraemic patients and 16 control sub jects were examined. Anisotropy of DPH-probe. measured at 37 degrees C , was significantly higher in control (0.2236+/-0.0050) than in uraemi c platelets (0.1969+/-0.0082; p<0.01). There was no difference between control (109.8+/-6.0 nM) and uraemic platelets (100.0+/-7.3 nM) when the basal [Ca2+](i) in resting platelets was determined. Activation of platelets by ADP (12.5 mu M) or by thrombin (0.1 U/ml) resulted in an increase in [Ca2+](i). It was significantly higher (p<0.003 for ADP and p<0.009 for thrombin, respectively) in control platelets (383.6+/ -56.3 nM and 2031.0+/-298.8 nM, respectively) than in uraemic ones (19 1.0+/-121.3 nM and 838.7+/-144.1 nM, respectively). The amount of rele ased Ca2+ was higher in control platelets activated by both ADP and th rombin (157.6+/-21.4 nM and 409.3+/-71.0 nM, respectively) than in ura emic platelets (76.7+/-15.7 nM and 203.0+/-29.3 nM, respectively) and the differences were significant (p<0.01 and p<0.01, respectively). T hese results indicate an abnormal intracellular Ca2+ mobilization in u raemic platelets Both increased membrane fluidity and decreased Ca2+ m obilization should be considered as a possible reason of reduced fibri nogen receptor exposure on uraemic platelets.