Acid evoked thermal hyperalgesia involves peripheral P2Y1 receptor mediated TRPV1 phosphorylation in a rodent model of thrombus induced ischemic pain
1 Department of Veterinary Physiology, College of Veterinary Medicine and Research Institute for Veterinary Science, Seoul National University, Seoul 151-742, Republic of Korea
2 Department of Maxillofacial Tissue Regeneration, School of Dentistry, Kyung Hee University, Seoul 130-701, Republic of Korea
3 Laboratory of Molecular Signal Transduction, Center for Neural Science, Korea Institute of Science and Technology (KIST), Seoul 136-791, Republic of Korea
4 Acupuncture, Moxibustion & Meridian Research Group, Medical Research Division, Korea Institute of Oriental Medicine, Daejeon, Republic of Korea
5 Department of Veterinary and Biomedical Sciences, College of Veterinary Medicine, University of Minnesota, St Paul, MN 55108, USA
6 Pain Cognitive Function Research Center, Dental Research Institute and Department of Neurobiology and Physiology, Department of Brain and cognitive Sciences, Seoul National University, Seoul 110-749, South Korea
Molecular Pain 2014, 10:2 doi:10.1186/1744-8069-10-2Published: 9 January 2014
We previously developed a thrombus-induced ischemic pain (TIIP) animal model, which was characterized by chronic bilateral mechanical allodynia without thermal hyperalgesia (TH). On the other hand we had shown that intraplantar injection of acidic saline facilitated ATP-induced pain, which did result in the induction of TH in normal rats. Because acidic pH and increased ATP are closely associated with ischemic conditions, this study is designed to: (1) examine whether acidic saline injection into the hind paw causes the development of TH in TIIP, but not control, animals; and (2) determine which peripheral mechanisms are involved in the development of this TH.
Repeated intraplantar injection of pH 4.0 saline, but not pH 5.5 and 7.0 saline, for 3 days following TIIP surgery resulted in the development of TH. After pH 4.0 saline injections, protein levels of hypoxia inducible factor-1α (HIF-1α) and carbonic anhydrase II (CA II) were elevated in the plantar muscle indicating that acidic stimulation intensified ischemic insults with decreased tissue acidity. At the same time point, there were no changes in the expression of TRPV1 in hind paw skin, whereas a significant increase in TRPV1 phosphorylation (pTRPV1) was shown in acidic saline (pH 4.0) injected TIIP (AS-TIIP) animals. Moreover, intraplantar injection of chelerythrine (a PKC inhibitor) and AMG9810 (a TRPV1 antagonist) effectively alleviated the established TH. In order to investigate which proton- or ATP-sensing receptors contributed to the development of TH, amiloride (an ASICs blocker), AMG9810, TNP-ATP (a P2Xs antagonist) or MRS2179 (a P2Y1 antagonist) were pre-injected before the pH 4.0 saline. Only MRS2179 significantly prevented the induction of TH, and the increased pTRPV1 ratio was also blocked in MRS2179 injected animals.
Collectively these data show that maintenance of an acidic environment in the ischemic hind paw of TIIP rats results in the phosphorylation of TRPV1 receptors via a PKC-dependent pathway, which leads to the development of TH mimicking what occurs in chronic ischemic patients with severe acidosis. More importantly, peripheral P2Y1 receptors play a pivotal role in this process, suggesting a novel peripheral mechanism underlying the development of TH in these patients.