title: A few immobilized thrombins are sufficient for platelet spreading.
abstract: Eukaryotic cells respond to signaling molecules with picomolar to nanomolar sensitivities. However, molar concentrations give no suggestion of the sufficient number of molecules per cell and are confusing when referring to physiological situations in which signaling molecules act in an immobilized state. Here, we studied platelet adhesion by thrombin, a key step in normal hemostasis and pathological arterial thrombosis. We generated a biofunctional nanosheet surface to mimic the in vivo solid-state interaction between platelets and thrombin at sites of injured tissues. We observed that <10 molecules readily activate platelets with high specificity, resulting in platelet adhesion and spreading. This number is much lower than expected from previous experiments in solution, in which the sole activation of platelets required a >1000-fold stoichiometric excess of thrombin. We conclude that immobilizing thrombin apposed to the membrane receptor allows platelets to respond with very high sensitivity. Moreover, we propose that irreversible cell activation may require several ligands to avoid activation by single, mislocalized signaling molecules.
authors.affiliation: Membrane Biochemistry, Life and Medical Sciences (LIMES) Institute, University of Bonn, Bonn, Germany.
authors.forename: Yosuke
authors.initials: Y
authors.lastname: Okamura
authors.forename: Roman
authors.initials: R
authors.lastname: Schmidt
authors.forename: Ines
authors.initials: I
authors.lastname: Raschke
authors.forename: Maik
authors.initials: M
authors.lastname: Hintze
authors.forename: Shinji
authors.initials: S
authors.lastname: Takeoka
authors.forename: Alexander
authors.initials: A
authors.lastname: Egner
authors.forename: Thorsten
authors.initials: T
authors.lastname: Lang
mesh_terms: D000327:Adsorption; D001792:Blood Platelets / Q000166:cytology / Q000201:enzymology* / Q000502:physiology*; D004800:Enzymes, Immobilized / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D019344:Lactic Acid / Q000737:chemistry; D049329:Nanostructures / Q000737:chemistry; D010973:Platelet Adhesiveness; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000378:metabolism; D011091:Polyesters; D011108:Polymers / Q000737:chemistry; D013917:Thrombin / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D004800:Enzymes, Immobilized; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D011091:Polyesters; D011108:Polymers; D019344:Lactic Acid; C033616:poly(lactide); D013917:Thrombin