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.