Orientation of platelets on the surfaces of glass and Teflon plates as studied by a spin label technique.

Platelets were found by a spin label technique to orient on flat surfaces of glass as well as of Teflon. This kind of platelet orientation was not caused by centrifugation or partial dehydration of the membrane preparation as employed usually to make oriented planar multilayers of biological membranes on the surface of a supporting plate (1-8), but was considered to be closely related to the adhesion or the aggregation properties of platelets. The amount of oriented platelets varied depending on the platelet treatment and was estimated from a computer simulation of the observed ESR spectra to be about one-half of that of the non-oriented ones in the case of thrombin-treated platelets. This technique may be useful as a new tool to explore the adhesion or aggregation properties of platelets.