Activation of thin-fiber muscle afferents by a P2X agonist in cats

The responses of group III and IV triceps surae muscle afferents to intra-arterial injection of α,β-methylene ATP (50 μg/kg) was examined in decerebrate cats. We found that this P2X₃ agonist stimulated only three of 18 group III afferents but 7 of 9 group IV afferents (P < 0.004). The three group III afferents stimulated by α,β -methylene ATP conducted impulses below 4 m/s. Pyridoxal phosphate-6-azophenyl-2′,4′-disulfonic acid, a P2-receptor antagonist, prevented the stimulation of these afferents by α,β -methylene ATP. We conclude that P2X₃ agonists stimulate only the slowest conducting group III muscle afferents as well as group IV afferents.