Journal
AMERICAN JOURNAL OF PHYSIOLOGY-HEART AND CIRCULATORY PHYSIOLOGY
Volume 293, Issue 5, Pages H2995-H3000Publisher
AMER PHYSIOLOGICAL SOC
DOI: 10.1152/ajpheart.00743.2007
Keywords
group III muscle afferents; group IV muscle afferents; ATP; cats; renal sympathetic nerve activity; neural control of the circulation
Funding
- NIAMS NIH HHS [AR051503] Funding Source: Medline
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Blockade of purinergic 2 receptors attenuates the mechanoreceptor component of the exercise pressor reflex. Am J Physiol Heart Circ Physiol 293: H2995-H3000, 2007. First published August 31, 2007; doi:10.1152/ajpheart.00743.2007.- The finding that pyridoxalphosphate-6-azophenyl-2,4-disulfonic acid ( PPADS), a P-2 antagonist, attenuated the pressor response to calcaneal tendon stretch, a purely mechanical stimulus, raises the possibility that P2 receptors sensitize mechanoreceptors to static contraction of the triceps surae muscles. The mechanical component of the exercise pressor reflex, which is evoked by static contraction, can be assessed by measuring renal sympathetic nerve activity during the first 2-5 s of this maneuver. During this period of time, group III mechanoreceptors often discharge explosively in response to the sudden tension developed at the onset of contraction. In decerebrated cats, we, therefore, examined the effect of PPADS ( 10 mg/kg) injected into the popliteal artery on the renal sympathetic and pressor responses to contraction and stretch. We found that PPADS significantly attenuated the renal sympathetic response to contraction, with the effect starting 2 s after its onset and continuing throughout its 60-s period. PPADS also significantly attenuated the renal sympathetic nerve response to stretch, but did so after a latency of 10 s. Our findings lead us to conclude that P2 receptors sensitize group III muscle afferents to contraction. The difference in the onset latency between the PPADS-induced attenuation of the renal sympathetic response to contraction and the renal sympathetic response to stretch is probably due to the sensitivities of different populations of group III afferents to ATP released during contraction and stretch.
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