Role Of Surface Negative Charge In Platelet Aggregation

The relationship between aggregability and electrophoretic mobility (EPM) was studied to clarify the role of surface negative charge in platelet function. 1. Human platelets were washed 3 times with Phillip’s buffer (pH 7.4), resuspended to 107 platelets/ml in modified Zeiller and Hannig’s buffer with 1 mM EDTA and incubated with various concentrations of ADP, adrenaline, thrombin and ristocetin at 37°C for 3 min. Without further washing, mean EPM of about 700 platelets was determined by the automatic Laser Zee System 3000 with good reproducibility with less than 1 % variation coefficient for 5 measurements. In all experiments, aggregating agents were dissolved in physiologic saline to obtain the same solution conductance both in test and control platelet suspensions to which saline alone was added. Neither 1-100 uM ADP nor 5-500 μM adrenaline had any effect on platelet EPM. Thrombin decreased EPM with dose response relation with -1.692±0.014 μm/sec/V/cm without thrombin, -1.580±0.084 with o725 , -1.578±0.001 with 1.0, -1.454±0.018 with 2.0 and -1.289±0.004 with 5.0 U/ml of thrombin. Ristocetin had decreasing effect on EPM at 0.2 mg/ml or less. After addition of above aggregating agents, the washed platelets did not aggregate under phase contrast microscopy. 2. EPM of washed platelets were compared with aggregability in the PRP collected from 33 clinical cases with various degrees of aggregation. There was no correlation between EPM and secondary and maximum aggregation induced by any of these four agents. However, intensity of primary aggregation by adrenaline correlated with EPM (r= 0.485, P<0.01). The same tendency was observed in primary aggregation by ADP. 3. Treatment of washed rabbit platelets with increasing doses of neuraminidase resulted in increasing aggregation by ADP and collagen associated with decrease in EPM. These findings suggested that platelet surface negative charge may be regulatory role in initiation of platelet activation.