Single-cell measurements of fibrinogen binding demonstrate functional synergy between P2Y₁ and P2Y₁₂ receptors in primary murine megakaryocytes. (A) Mouse marrow cells (Ai) were bathed in Oregon green–labeled fibrinogen, and fluorescence images were acquired within a 3-μm z-section at the midplane of a megakaryocyte by confocal microscopy before (Aii) and after (Aiii) the addition of 30 μM ADP. Images were analyzed as described in detail in “Materials and methods”; f is the fluorescence level, f_e is the average extracellular fluorescence, and f_p is the average fluorescence measured around the cell periphery. (B) f/f_e across the center of control, P2Y₁^–/– and AR-C69931MX–treated MKs before (i) and 2 minutes after (ii) the addition of 30 μM ADP. (C) Average f_p/f_e ratios before (□) and after (▦) the addition of 30 μM ADP for control, P2Y₁^–/–, and AR-C69931MX-treated MKs (n = 10 for each). ***Statistical significance of P < .001 compared with control.