Ultrastructure of platelets and platelet-surface interactions

Abstract

Human platelets have a discoid form in their resting state. In order to relate structure to function, the anatomy of the platelet has been divided into several zones [1,2]. The peripheral zone consists of membranes and closely associated structures providing the surface of the platelet and the walls of the channels making up the surface-connected open canalicular system (OeS) (Figure 1). An exterior coat or glycocalyx, rich in glycoproteins [3], provides the outermost covering of the peripheral zone. The middle layer of the peripheral zone is a typical unit membrane, rich in phospholipids, that serves as an essential surface for interaction with coagulation factors. Glycoproteins are embedded in the lipid bilayer of the unit membrane. They provide the receptors for stimuli triggering platelet activation. Heads of the glycoproteins extend to the extracellular space forming the glycocalyx. The tails are usually related to the submembrane zone and translate signals received on the outside surface into chemical messages and physical alterations required for platelet activation.The sol-gel zone is the matrix of the platelet cytoplasm. It contains several fiber systems in various states of polymerization (cytoskeleton). These systems support the discoid shape in resting platelets and provide a contractile system involved in shape change, pseudopod extension, internal contraction and secretion. Elements of the contractile system constitute approximately 30-50 per cent of the total platelet protein.The organelle zone consists of granules, electron dense bodies, peroxisomes, lysosomes, mitochondria, as well as discrete particles of glycogen randomly dispersed in the cytoplasm. It serves in metabolic processes and for the storage of enzymes, non-metabolic adenine nucleotides, serotonin, a variety of protein constituents and calcium.

Sulphated hyaluronic acids: a chemical and biological characterisation

“…35 Thus the di †erent abilities of Hyal and to cause platelet aggregation can be explained HyalS x by the di †erent chemical structures of the tested samples. Hyal presents only COO~groups as negative charges and is not able to repel the platelets.…”

The effect of topography of polymer surfaces on platelet adhesion

“…transformations as platelets activated in suspension [42]. In this study, adhered platelets were first stained with PAC -1 prior to fixation because PAC-1 does not bind to formaldehyde-fixed platelets [43].…”

HEMATOLOGY: ISSUES IN THE DIALYSIS PATIENT: Platelet Dysfunction and End‐Stage Renal Disease

“…These alterations in the platelet contractile system can contribute to impaired platelet motility and secretory function in advanced renal failure. Impaired contractility may also contribute to defective platelet interaction with artificial surfaces (26).…”