Bromoenol lactone enhances the permeabilization of rat submandibular acinar cells by P2X 7 agonists

The permeabilizing effect of P2X 7 agonists was tested in rat submandibular acinar cells using the uptake of ethidium bromide as an index. The uptake of ethidium bromide by acini incubated at 37°C in the presence of 1 m M ATP increased with time and reached after 5 min about 10% of maximal uptake measured in the presence of digitonin. The response to ATP was dose‐dependent (half‐maximal concentration around 40 μ M ) and it was decreased when the temperature was lowered to 25°C. Benzoyl‐ATP reproduced the response to ATP (half‐maximal concentration around 10 μ M ). UTP or 2‐methylthioATP had no effect. The permeabilization in response to ATP was blocked by oxidized ATP and by magnesium and inhibited by Coomassie blue. ATP increased the activity of a calcium‐insensitive phospholipase A 2 (iPLA 2 ). Bromoenol lactone (BEL) inhibited the iPLA 2 stimulated by ATP but potentiated the uptake of ethidium bromide in response to the purinergic agonist. From these results it is concluded that the activation of P2X 7 receptors permeabilizes rat submandibular acinar cells. The pore‐forming activity of the receptor might be negatively regulated by the concomitant activation of the iPLA 2 by the receptor.British Journal of Pharmacology (2000) 129 , 703–708; doi: 10.1038/sj.bjp.0703124