Diadenosine pentaphosphate is more potent than ATP at P2X receptors in isolated rat vagus nerve

The effects of diadenosine pentaphosphate (Ap5A), diadenosine tetraphosphat e (Ap4A), alpha,beta -methyleneATP (alpha,beta -meATP), and ATP were studie d on the excitability of unmyelinated axons in isolated rat vagus nerve by means of a computerized threshold tracking technique. All purinergic compou nds produced an increase in excitability, however, only the effects of alph a,beta -meATP and of Ap5A were strongly reduced by 2'- (or 3') -O-(2,4,6-tr initrophenyl)-ATP (TNP-ATP), a selective blocker for P2X(1), P2X(3), and he teromeric P2X(2/3) receptors. The rank order of potency for TNP-ATP-sensiti ve excitation was determined as follows (30 muM each): alpha,beta -meATP > Ap5A > > Ap4A = ATP. These data suggest that Ap5A might be an important nat urally occurring agonist for P2X receptors at the axonal membrane of unmyel inated, including nociceptive, nerve fibres. NeuroReport 12:679-682 (C) 200 1 Lippincott Williams & Wilkins.