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PubMedDate not supplied

Shear stress induces not only platelet aggregation but also platelet-tumor cell interaction.

To investigate the interaction between platelets and tumor cells under well-defined flow conditions, the effect of tumor cells on platelet aggregation induced by shear stress was studied using a cone and plate viscometer adapted for measuring transmitted light intensity. Aggregation was markedly enhanced by HMV-1 cells in a cell number-dependent fashion under shear stress of 12 dyne/cm2. Enhancement was not observed at a high shear stress of 108 dyne/cm2. A monoclonal antibody against GPIIb/IIIa, 7E3 completely abolished enhancement of aggregation by HMV-1. Apyrase had similar inhibitory effects. Scanning electronmicroscopy showed that direct contacts of platelets with HMV-1 cells could be demonstrated when platelet-platelet interaction was inhibited by 7E3 or apyrase. These results may indicate that, at a shear stress of 12 dyne/cm2, direct contacts of platelets and HMV-1 cells may trigger enhancement of platelet aggregation.

Blood Flow Velocity↗

PubMedDate not supplied

Change in intracellular calcium ions during shear induced platelet aggregation.

The authors have developed a method to measure intracellular calcium ion concentration ([Ca2+]i) during shear-induced platelet aggregation. A cone and plate viscometer was adapted for continuous recording of both light transmission and fluorescence intensity. Citrated platelet rich plasma was incubated with Indo-1AM at a concentration of 10 microns for 30 min at 37 degrees C, then applied to the albumin density gradient to prepare washed platelets. To Indo-1AM loaded washed platelets, fibrinogen, and von Willebrand factor (vWf) were added, with 1 mM CaCl2. Platelets were then exposed to changing shear stress (6-108 dynes/cm2) for simultaneous measurement of aggregation and [Ca2+]i. [Ca2+]i in resting platelets was estimated as approximately 100 nM. At low shear stress (10-20 dynes/cm2), [Ca2+]i did not change. In contrast, a marked increase in [Ca2+]i was observed concurrent with aggregation at high shear stress (100-108 dynes/cm2). However, no increase was seen in the presence of 1 mM EGTA. The increase was prevented by monoclonal antibodies against GPIb or vWf, which inhibited vWf binding to GPIb. A monoclonal anti-vWf antibody, which inhibited vWf binding to the GPIIb/IIIa complex, did not affect [Ca2+]i increase during high shear induced platelet aggregation. These results suggest that binding of vWf to GPIb may trigger Ca2+ influx.

Blood Flow Velocity↗