ASICs are required for immediate exercise-induced muscle pain and are downregulated in sensory neurons by exercise training

Abstract

ASICs are required for immediate exercise-induced muscle pain and are downregulated in sensory neurons by exercise training. J Appl Physiol 129: 17–26, 2020. First published May 28, 2020; doi:10.1152/japplphysiol.00033.2020.—Exercise training is an effective therapy for many pain-related conditions, and trained athletes have lower pain perception compared with unconditioned people. Some painful conditions, including strenuous exercise, are associated with elevated levels of protons, metabolites, and inflammatory factors, which may activate receptors and/or ion channels, including acid-sensing ion channels (ASICs), on nociceptive sensory neurons. We hypothesized that ASICs are required for immediate exercise-induced muscle pain (IEIP) and that exercise training diminishes IEIP by modulating ASICs within muscle afferents. We found high-intensity interval training (HIIT) reduced IEIP in C57BL/6 mice and diminished ASIC mRNA levels in lumber dorsal root ganglia, and this downregulation of ASICs correlated with improved exercise capacity. Additionally, we found that ASIC3 ‒/‒ mice did not develop IEIP; however, the exercise capacity of ASIC3 ‒/‒ was similar to wild-type mice. These results suggest that ASICs are required for IEIP and that diminishment of IEIP after exercise training correlates with downregulation of ASICs in sensory neurons. NEW & NOTEWORTHY Exercise performance can be limited by the sensations of muscle fatigue and pain transmitted by muscle afferents. It has been proposed that exercise training abrogates these negative feedback signals. We found that acid-sensing ion channels (ASICs) are required for immediate exercise-induced muscle pain (IEIP). Moreover, exercise training prevented IEIP and was correlated with downregulation of ASICs in sensory neurons.