Fate of released ATP: possible role in leukocyte chemotaxis.

(A) The intracellular ATP concentration is in the 5 to 10 mM range; thus, an ATP gradient capable of driving leukocyte chemotaxis by acting at P2Y receptors is likely to occur at sites of cell or tissue damage. (B) ATP released into the pericellular milieu can either ligate P2Y or P2X receptors or be hydrolyzed by plasma membrane ecto-ATPases or ecto-ATP diphosphohydrolase (CD39). Hydrolysis of AMP by 5′-nucleotidase generates adenosine that activates P1 purinergic receptors.