Platelet function in MAGP1-deficient mice. (A) The percentage of platelets that aggregate in response to different levels of collagen is the same for both genotypes. (B) The presence of MAGP1 (50 μg/mL) has no effect on human platelet aggregation induced by various agonists, including collagen (Col, 10 μg/mL), adenosine 5′-diphosphate (ADP, 20 μM), arachidonic acid (AA, 500 μg/mL), and epinephrine (Epi, 300 μM). Aggregation was monitored by measuring light transmission through a suspension of stirred washed platelets (1-3 × 10⁸/mL for mouse and 2 × 10⁸/mL for human) using an aggregometer. Data are expressed as either the slope of the aggregation curve or as percentage of cells that underwent aggregation. (C) Recombinant bovine MAGP1 has no effect on the ristocetin cofactor activity of human plasma. All experiments contained normal human plasma diluted 1:1 with Tris-buffered saline, yielding 50% ristocetin cofactor activity in the control sample. Error bars indicate mean plus or minus standard deviation of 4 experiments. None of the values differed significantly (P ≥ .25).