Effect of fibrinogen on TG- or ADP-evoked actin polymerization in platelets.

Control human platelets (A) or dimethyl BAPTA-loaded platelets (B) were treated with TG (200 nM), ADP (5 μM), or the vehicle (HBS) in the absence or presence of 1 mg/mL fibrinogen. Samples were removed 5 seconds before and 3 minutes after the addition of the stimuli, and actin filament content was determined as described in “Materials and methods.” Values given are actin filament content as percentages of basal (HBS-treated platelets) and are expressed as mean ± SE from 6 independent determinations. *P < .05; **P < .01; ***P < .001. (C) Human platelets were stimulated with TG (200 nM) or ADP (5 μM), and 10 seconds later fibrinogen (1 mg/mL) or the vehicle (HBS) was added. Samples were removed 5 seconds before and 3 minutes after the addition of the stimuli, and actin filament content was determined as described in “Materials and methods.” Values given are actin filament contents as percentages of basal (nontreated platelets) and are expressed as mean ± SE from 6 independent determinations.