FLOW-INDUCED DETACHMENT OF ADHERENT PLATELETS FROM FIBRINOGEN-COATED SURFACE

A study of the shear forces under which adherent platelets of differen t morphologies can be detached from surfaces was carried out using a n ewly designed tapered flow chamber, which covered the entire shear ran ge of physiological circulation. Platelets that naturally settled on a fibrinogen-coated surface were exposed to shear flow and were subsequ ently processed for scanning electron microscopic observation. We foun d that 1) the density of platelets remaining after flow exposure decre ased with local shear stress, 2) adherent platelets of different morph ologies withstood different levels of shear stress: most round cells a nd 40% of the cells that had a few short pseudopods were detached at < 10 dyn/cm(2), whereas most spread cells could withstand 50 dyn/cm(2), 3) pulsatile flow was more effective in removing adherent platelets th an equivalent steady flow, 4) cytochalasin D and colchicine retarded p latelet shape change and made them more easily detached by shear force s, and 5) metabolic energy-depleted platelets spread readily and forme d shear-resistant clumps. Our observations indicated that adherent pla telets of different morphologies on a fibrinogen-coated surface could withstand different levels of flow shear stress.