An overview of platelet structural physiology

Abstract

Marion Barnhart and her colleagues used light, phase contrast and scanning electron microscopy to provide a clear picture of platelet surface changes developing in response to aggregating agents. This review, in honor of Marion and her work, has sought to expand the horizon provided through study of surface alterations by peeling back the membrane of the platelet to reveal the dynamic world within. A cytoskeleton consisting of a circumferential microtubule and submembrane actin filaments supports the discoid shape of the resting cell. Following exposure to aggregating agents in suspension, to foreign surfaces or denuded blood vessels and to fibrin strands during clot retraction, the state of assembly and organization of actin and location of the microtubule undergo dramatic alterations. There are differences in the cytoskeletal organization of platelets activated in suspension or on surfaces, during spreading on damaged blood vessels or in the process of clot retraction; yet, the similarities are far more impressive than the differences. The ability to assemble its cytoskeleton and adapt it to a variety of conditions requiring the exercise of contractile force makes the platelet a unique form of muscle cell.