PolyP and C1-INH colocalize in activated human platelets. Human platelets were plated onto glass coverslips in the resting state (top panels) or after 2 minutes of activation with 100 nM of the phorbol ester, phorbol 12-myristate 13-acetate, and 1 μM of calcium ionophore A23187. After fixation and permeabilization, the platelets were stained as described in “Materials and methods” to detect C1-INH (left panels, green) and polyP (middle panels, red) by confocal microscopy. The right panels reveal the merged images. In resting platelets, C1-INH is detected in α granules and on the cell surface, and polyP is found in dense granules. After activation, C1-INH and polyP coalesce in the center of the platelets where they colocalize (yellow, right bottom panel). Size bars, 10 μm. Results are representative of 3 independent experiments.