Background: Acid-sensing ion channels 2 and 3 (ASIC2 and ASIC3, respectively) have been implicated as putative mechanotransducers. Because mechanical hyperalgesia is a prominent consequence of nerve injury, we tested whether male and female ASIC2 or ASIC3 knockout mice have altered responses to mechanical and heat stimuli at baseline and during the 5 weeks after spinal nerve ligation.
Methods: Age-matched, adult male and female ASIC2 knockout (n=21) and wild-type (WT; n=24) mice or ASIC3 knockout (n=20) and WT (n=19) mice were tested for sensitivity to natural stimuli before and after spinal nerve ligation surgery. All animals were first tested for baseline sensitivity to mechanical and heat stimuli and in a novel dynamic mechanical stimulation test. The same testing procedures were then repeated weekly after spinal nerve injury.
Results: Compared with their respective WT counterparts, ASIC2 and ASIC3 knockout mice had normal baseline sensitivity to standard mechanical and heat stimuli. However, when exposed to a novel stroking stimulus to test sensitivity to dynamic mechanical stimulation, ASIC3 knockout mice were significantly more sensitive than were WT mice. After spinal nerve ligation, ASIC2 and ASIC3 knockout mice developed mechanical and heat hyperalgesia comparable with that of their respective WT controls. In addition, in both experiments, female mice were more sensitive than male mice to heat at baseline and after the nerve injury.
Conclusions: We conclude that ASIC2 and ASIC3 channels are not directly involved in the development or maintenance of neuropathic pain after spinal nerve ligation. However, the ASIC3 channel significantly modulates the sensing of dynamic mechanical stimuli in physiologic condition.