Electron Microscopy of von Willebrand Factor

The relationship between the degree of ristocetin-induced platelet agglutination and the size of von Willebrand factor (vWF) involved in it was evaluated. Four hundred microliters of formalin-fixed platelet suspension and 50μl of purified vWF were placed in a cuvette in the platelet aggregometer. Agglutination curves were recorded by adding 50μl of various concentration of ristocetin. vWF molecules in each supernatant were examined by SDS-polyacrylamide-agarose gel electrophoresis (SDS-PAGE) and electron microscopy. By SDS-PAGE, no differences were seen in size distribution of vWF among each supernatant. By electron microscopy, although vWF in the supernatants after agglutination were somewhat folded, the numbers of nodules in vWF multimers in each supernatant after various degrees of agglutination were not different from that of vWF multimers with no agglutination. We conclude that there was no difference in the size distribution of vWF involved in the ristocetin-induced platelet agglutination.