The inhibitor protein of the F1F0-ATP synthase is associated to the external surface of endothelial cells

The ATPase inhibitor protein (IP) of mitochondria was detected in the plasma membrane of living endothelial cells by flow cytometry, competition assays, and confocal microscopy of cells exposed to IP antibodies. The plasma membranes of endothelial cells also possess β-subunits of the mitochondrial ATPase. Plasma membranes have the capacity to bind exogenous IP. TNF-α decreases the level of β-subunits and increases the amount of IP, indicating that the ratio of IP to β-subunit exhibits significant variations. Therefore, it is probable that the function of IP in the plasma membrane of endothelial cells is not limited to regulation of catalysis.