Endothelial P2 receptor expression after inflammatory stimulation. HMEC-1 cells were exposed to 10 ng/mL TNF-α for 24 hours. Receptor expression levels of the 15 known P2 receptors were determined in controls and TNF-α–stimulated cells by real-time RT-PCR. Data were calculated relative to the internal housekeeping gene β-actin and are expressed as mean ± SD fold change compared with the control (without TNF-α) (n = 3-4). Primers and PCR conditions are summarized in the supplemental data.