Spin label measurement of platelet alignment in a clot induced by isometric tension.

A spin label technique was applied to examine the alignment of platelet membranes in the platelet-fibrin clot. The ESR spectrum of the clot in the control experiment was typical of isotropically oriented membranes, while the ESR spectrum of the clot which was kept isometric was quite different from that of the control experiment. These spectra were simulated with a computer and explained to indicate that the shape of platelets in the clot was transformed to a cylindrical form under the isometric tension so that axes of all membrane cylinders were directed parallel to the generated force.