VWF-string cleavage in the presence of platelets is calcium-independent. (A-B) HEPES buffer containing platelets with and without 1.5 mM calcium was perfused over stimulated HUVECs for 5 minutes. 1 U/mL ADAMTS13 along with 2′,7′-Bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein–labeled platelets was then introduced (shown by arrow at t = 0 s) in the same buffer at either 1 dyn/cm2 (A) or 2.5 dyn/cm2 (B). Percent change/decrease in VWF string length after ADAMTS13 addition was measured. No significant difference was noted between calcium and calcium-free runs. (C) Representative time course of VWF-string cleavage, marked by successive loss of platelets. White arrows indicate stretching of interplatelet distance before cleavage. Data are from 4 to 7 experiments under each condition.
