ECs plated on glass cover slips were loaded with 5 μM fura-2 AM (Invitrogen, Carlsbad, CA) in 1 ml of basal medium as previously reported [18] . The cover slips with ECs were inserted diagonally into 1 cm acrylic cuvettes filled with 3 ml of basal medium at 37°C. Fura-2 fluorescence was measured with an Aminco-Bowman Series 2 luminescence spectrometer (SLM/Aminco, Urbana, IL) at excitation wavelengths of 340 and 380 nm and emission wavelength of 510 nm. The cover slips with ECs were then moved to 35 mm dishes, treated with PM suspension, and incubated for 15 minutes at 37°C in 95% O 2 and 5% CO 2 . After every 15-minute incubation, the coverslips were withdrawn from the dish and inserted back into the acrylic cuvettes for Fura-2 fluorescence measurement, then returned to the dish with the resuspended PM preparation for another incubation period (15-60 min).