Alteration of spontaneous firing rate of primary myelinated afferents by ATP in adjuvant-induced inflamed rats

The action of adenosine 5'-triphosphate (ATP) on primary myelinated mechano sensitive afferents was investigated in adjuvant-induced inflamed rats. ATP injected intravenously increased the spontaneous firing rate in most of th e A fibers from sciatic nerve innervating inflamed hindpaw, whereas it affe cted only a few units in normal rats. The effects of ATP were blocked or at tenuated by competitive P2 receptor antagonist suramin or reactive blue 2 i n most of the fibers tested. Degranulation of mast cells with compound 48/8 0 did not change the response rate of afferents to ATP in inflamed rats whi le chemical sympathectomy with 8-hydroxydopamine decreased it to some exten t, suggesting an involvement of sympathetic efferents in mediating ATP effe cts. The results support the view that ATP could change the activity of lar ge mechanosensitive afferents via P2 receptors under state of inflammation, which may be related to touch-evoked pain. (C) 2001 Elsevier Science Inc.