Bromoenol lactone enhances the permeabilization of rat submandibular acinar cells by P2X7 agonists

Abstract

1. The permeabilizing effect of P2X7 agonists was tested in rat submandibular acinar cells using the uptake of ethidium bromide as an index. 2. The uptake of ethidium bromide by acini incubated at 37°C in the presence of 1 mM ATP increased with time and reached after 5 min about 10% of maximal uptake measured in the presence of digitonin. 3. The response to ATP was dose-dependent (half-maximal concentration around 40 μM) and it was decreased when the temperature was lowered to 25°C. 4. Benzoyl-ATP reproduced the response to ATP (half-maximal concentration around 10 μM). UTP or 2-methylthioATP had no effect. 5 The permeabilization in response to ATP was blocked by oxidized ATP and by magnesium and inhibited by Coomassie blue. 6. ATP increased the activity of a calcium-insensitive phospholipase A2 (iPLA2). 7. Bromoenol lactone (BEL) inhibited the iPLA2 stimulated by ATP but potentiated the uptake of ethidium bromide in response to the purinergic agonist. 8. From these results it is concluded that the activation of P2X7 receptors permeabilizes rat submandibular acinar cells. The pore-forming activity of the receptor might be negatively regulated by the concomitant activation of the iPLA2 by the receptor.