Platelet adhesion to low-density fibrinogen leads to more rapid and sustained calcium response. Platelets loaded with calcium-sensitive dyes were added to wells coated with low- or high-density fibrinogen, and the cytosolic calcium fluxes during the first 30 minutes of the adhesion process were recorded using confocal microscopy as described in “Materials and methods” (Video S3). The adherent platelets were then analyzed according to their morphology and the characteristics of their calcium responses. (A) Population analysis demonstrated that most platelets adherent to high-density fibrinogen did not show any elevation in intracellular Ca²⁺ (*P < .001 high vs low-density fibrinogen, n = 3), whereas on low-density fibrinogen, approximately 40% of adherent platelets showed sustained Ca²⁺ oscillation (**P = .01). (B) Selected single platelet recordings of intracellular Ca²⁺ fluxes typical of nonresponsive platelet on high-density fibrinogen, a transient Ca²⁺ elevation in a platelet on high-density fibrinogen, and sustained oscillatory Ca²⁺ response in a platelet on low-density fibrinogen. Results are presented as mean ± SD.