Wortmannin inhibits the exposure of actin filament barbed ends in human platelets activated by CRP.

The rate of pyrene-actin assembly in lysates from resting and CRP-activated platelets was determined. Platelets were preincubated with or without 50 nmol/L wortmannin for 15 minutes. Resting or CRP-activated platelets for 2 minutes, permeabilized with Triton X-100, were added to 1 μmol/L pyrene-actin monomer to initiate actin assembly. Activity inhibited by 2 μmol/L cytochalasin B is defined as barbed-end actin assembly. Activity not inhibited by cytochalasin B is defined as pointed-end actin assembly. Results shown are representative of 4 experiments.