Retardation of Clot Retraction after Incubation of Platelets with Colchicine and Heavy Water

Abstract

BLOOD removed from the circulation and allowed to clot undergoes retraction, and the evidence is quite conclusive that retraction requires the presence of viable platelets^1,2. A circulating platelet is disk shaped, containing a marginal band of microtubules, a rather sparse layer of microfibres beneath the plasma membrane, and a variety of granules. With activation by clotting, the platelet peripheral microtubules disappear and hyaloplasmic microtubules appear, degranulation occurs, and the cells take on a constricted appearance because of the pseudopods that form and the centralizing of the organelles. The prevailing theory of clot retraction is that the withdrawal of the platelet pseudopods somehow provides the impetus for the compression of the inert extracellular fibrin. We suggested recently that in an analogous, non-mammalian clotting system the contraction of the whole haemostatic cell is related to clot contraction³.