title: Purinergic 2 receptor blockade prevents the responses of group IV afferents to post-contraction circulatory occlusion.
abstract: ATP, by activating purinergic 2 (P2) receptors on group III and IV afferents, is thought to evoke the metabolic component of the exercise pressor reflex. Previously we have shown that injection of PPADS, a P2 receptor antagonist, into the arterial supply of skeletal muscle of decerebrated cats attenuated the responses of group III and IV afferents to static contraction while the muscles were freely perfused. We have now tested the hypothesis that injection of PPADS (10 mg kg(-1)) attenuated the responses of group III (n = 13) and group IV afferents (n = 9) to post-contraction circulatory occlusion. In the present study, we found that PPADS attenuated the group III afferent responses to static contraction during circulatory occlusion (P < 0.05). Likewise, PPADS abolished the group IV afferent responses to static contraction during occlusion (P = 0.001). During a 1 minute period of post-contraction circulatory occlusion, four of the 13 group III afferents and eight of the nine group IV afferents maintained their increased discharge. A Fischer's exact probability test revealed that more group IV afferents than group III afferents were stimulated by post-contraction circulatory occlusion (P < 0.02). In addition, the nine group IV afferents increased their mean discharge rate over baseline levels during the post-contraction circulatory occlusion period, whereas the 13 group III afferents did not (P < 0.05). PPADS abolished this post-contraction increase in discharge by the group IV afferents (P < 0.05). Our findings suggest that P2 receptors on group IV afferents play a role in evoking the metabolic component of the exercise pressor reflex.
authors.affiliation: TB-172, Division of Cardiovascular Medicine, University of California Davis, Davis, CA 95616, USA. aekindig@ucdavis.edu
authors.forename: Angela E
authors.initials: AE
authors.lastname: Kindig
authors.forename: Shawn G
authors.initials: SG
authors.lastname: Hayes
authors.forename: Marc P
authors.initials: MP
authors.lastname: Kaufman
mesh_terms: D000818:Animals; D002415:Cats; D003326:Coronary Circulation / Q000502:physiology*; D004594:Electrophysiology; D006329:Heart Conduction System / Q000187:drug effects; D018485:Muscle Fibers, Skeletal / Q000187:drug effects; D009200:Myocardial Contraction / Q000502:physiology*; D009431:Neural Conduction; D009475:Neurons, Afferent / Q000187:drug effects*; D058919:Purinergic P2 Receptor Antagonists; D011732:Pyridoxal Phosphate / Q000031:analogs & derivatives / Q000494:pharmacology
chemical_list: D058919:Purinergic P2 Receptor Antagonists; C077792:pyridoxal phosphate-6-azophenyl-2',4'-disulfonic acid; D011732:Pyridoxal Phosphate