2.7. Adenosine concentration measurement in cell culture medium

Cell‐free supernatant was blotted on a Whatmann blot paper (6 mm diam.) prior to extraction using a mixture of methanol (400 µL) and internal standard (see above) for 90 minutes at 45°C. After extraction, an aliquot (350 μL) was evaporated to dryness at 60°C under nitrogen. Formic acid (0.1% in water; 150 µL) was added and vortexed prior to transfer into an HPLC auto‐sampler vial. Dosage was then performed using LC‐MS/MS as described above.