Article

Temperature modulates P2X receptor-mediated cardiovascular responses to muscle afferent activation.

Heart and Vascular Institute, Division of Cardiology, Department of Medicine, H047, Penn State College of Medicine, Milton S. Hershey Medical Center, 500 University Dr., Hershey, PA 17033, USA.
AJP Heart and Circulatory Physiology (impact factor: 3.71). 10/2006; 291(3):H1255-61. DOI:10.1152/ajpheart.01303.2005
Source: PubMed

ABSTRACT Static muscle contraction increases ATP release into the muscle interstitial space. Elevated ATP in muscle stimulates thin fiber muscle afferents and increases blood pressure via engagement of purinergic P2X receptors. In addition, ATP activates P2X receptors and enhances cardiovascular responses induced by stimulation of muscle mechanoreceptors. In this study, we examined whether elevated muscle temperature would attenuate and whether reduced temperature would potentiate P2X effects on reflex muscle responses. alpha,beta-Methylene ATP (alpha,beta-MeATP) was injected into the arterial blood supply of hindlimb muscle to stimulate P2X receptors, and muscle stretch was induced to activate mechanically sensitive muscle afferents as alpha,beta-MeATP was injected in 10 anesthetized cats. Femoral arterial injection of alpha,beta-MeATP (1.0 mM) increased mean arterial pressure (MAP) by 35+/-5 (35 degrees C), 26+/-3 (37 degrees C), and 19+/-3 mmHg (39 degrees C; P<0.05 vs. 35 degrees C), respectively. Muscle stretch (2 kg) elevated MAP. The MAP response was significantly enhanced 34% and 36% when alpha,beta-MeATP (0.2 mM) was arterially infused 5 min before muscle stretch at 35 degrees and 37 degrees C, respectively. However, as muscle temperature reached 39 degrees C, the stretch-evoked response was augmented only 6% by alpha,beta-MeATP injection, and the response was significantly attenuated compared with the response with muscle temperature of 35 degrees and 37 degrees C. In addition, we also examined effects of muscle temperature on alpha,beta-MeATP enhancement of the cardiovascular responses to static muscle contraction while the muscles were freely perfused and the circulation to the muscles was occluded. Because muscle temperature was 37 degrees C, arterial injections of alpha,beta-MeATP significantly augmented contraction-evoked MAP response by 49% (freely perfused) and 53% (ischemic condition), respectively. It is noted that this effect was significantly attenuated at a muscle temperature of 39 degrees C. These data indicate that the effect of P2X receptor on reflex muscle response is sensitive to alternations of muscle temperature and that elevated temperature attenuates the response.

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Keywords

35 degrees
 
35 degrees C
 
39 degrees C
 
5 min
 
arterial blood supply
 
arterial pressure
 
enhances cardiovascular responses induced
 
hindlimb muscle
 
increases blood pressure
 
MAP response
 
muscle interstitial space
 
muscle mechanoreceptors
 
Muscle stretch
 
muscle temperature
 
P2X receptor
 
purinergic P2X receptors
 
reflex muscle response
 
static muscle contraction
 
stimulate P2X receptors
 
stretch-evoked response
 

Zhaohui Gao