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Pain Research and Treatment
Volume 2012 (2012), Article ID 817347, 9 pages
http://dx.doi.org/10.1155/2012/817347
Research Article

ASICs Do Not Play a Role in Maintaining Hyperalgesia Induced by Repeated Intramuscular Acid Injections

1Graduate Program in Physical and Rehabilitation Science, University of Iowa, 1-252 MEB, Iowa City, IA 52242, USA
2Department of Internal Medicine, University of Iowa, E315 GH, Iowa City, IA 52242, USA
3Department of Chemistry, University of Utah, 315 S 1400 E RM 2020, Salt Lake City, UT 84112, USA
4Department of Anesthesia, University of Utah, 30 N 1900 E RM 3C444, Salt Lake City, UT 84132, USA

Received 14 June 2011; Revised 29 August 2011; Accepted 4 September 2011

Academic Editor: Brian E. Cairns

Copyright © 2012 Mamta Gautam et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Repeated intramuscular acid injections produce long-lasting mechanical hyperalgesia that depends on activation of ASICs. The present study investigated if pH-activated currents in sensory neurons innervating muscle were altered in response to repeated acid injections, and if blockade of ASICs reverses existing hyperalgesia. In muscle sensory neurons, the mean acid-evoked current amplitudes and the biophysical properties of the ASIC-like currents were unchanged following acidic saline injections when compared to neutral pH saline injections or uninjected controls. Moreover, increased mechanical sensitivity of the muscle and paw after the second acid injection was unaffected by local blockade of ASICs (A-317567) in the muscle. As a control, electron microscopic analysis showed that the tibial nerve was undamaged after acid injections. Our previous studies demonstrated that ASICs are important in the development of hyperalgesia to repeated acid injections. However, the current data suggest that ASICs are not involved in maintaining hyperalgesia to repeated intramuscular acid injections.