Transgenic Expression of a Dominant-Negative ASIC3 Subunit Leads to Increased Sensitivity to Mechanical and Inflammatory Stimuli

Abstract

Molecular and behavioral evidence suggests that acid-sensing ion channels (ASICs) contribute to pain processing, but an understanding of their precise role remains elusive. Existing ASIC knock-out mouse experiments are complicated by the heteromultimerization of ASIC subunits. Therefore, we have generated transgenic mice that express a dominant-negative form of the ASIC3 subunit that inactivates all native neuronal ASIC-like currents by oligomerization. Using whole-cell patch-clamp recordings, we examined the response properties of acutely isolated dorsal root ganglion neurons to protons (pH 5.0). We found that whereas 33% of the proton-responsive neurons from wild-type mice exhibited an ASIC-like transient response, none of the neurons from the transgenic mice exhibited a transient inward current. Capsaicin-evoked responses mediated by the TRPV1 receptor were unaltered in transgenic mice. Adult male wild-type and transgenic mice were subjected to a battery of behavioral nociceptive assays, including tests of thermal, mechanical, chemical/inflammatory, and muscle pain. The two genotypes were equally sensitive to thermal pain and to thermal hypersensitivity after inflammation. Compared with wild types, however, transgenic mice were more sensitive to a number of modalities, including mechanical pain (von Frey test, tail-clip test), chemical/inflammatory pain (formalin test, 0.6% acetic acid writhing test), mechanical hypersensitivity after zymosan inflammation, and mechanical hypersensitivity after intramuscular injection of hypotonic saline. These data reinforce the hypothesis that ASICs are involved in both mechanical and inflammatory pain, although the increased sensitivity of transgenic mice renders it unlikely that they are direct transducers of nociceptive stimuli.

ASIC3 in muscle mediates mechanical, but not heat, hyperalgesia associated with muscle inflammation

“…The current data, showing a loss of hyperalgesia in ASIC3−/− mice, are distinctly different from prior results from ASIC3−/− mice (Price et al, 2001;Chen et al, 2002), or dominantnegative ASIC3 transgenic mice that inactivates all ASIC-like currents (Mogil et al, 2005). These prior studies tested responses to cutaneous insult, i.e.…”

“…These prior studies tested responses to cutaneous insult, i.e. carrageenan, capsaicin, and acid and show either no or enhanced response to nociceptive stimuli after injury (Price et al, 2001;Chen et al, 2002;Mogil et al, 2005). Our prior study, and the current study tested responses to muscle insult and show a loss of mechanical hyperalgesia after insult .…”

“…Our prior study, and the current study tested responses to muscle insult and show a loss of mechanical hyperalgesia after insult . Mogil and colleagues attempted to test the effects of muscle insult in their dominantnegative ASIC3 transgenic mice; however, the wild-type controls for ASIC3 transgenic mice do not develop mechanical hyperalgesia to repeated intramuscular acid injections (Mogil et al, 2005), as we previously described (Sluka et al, 2004). Differences are likely related to the strain of the mouse since prior studies demonstrate strain differences in mechanical sensitivity and in different injury-induced animal models of pain (Mogil et al, 1999a;Mogil et al, 1999b).…”

ASIC3 Channels in Multimodal Sensory Perception

“…In contrast, Chen et al (51) found an increased sensitivity to thermal, mechanical, and acidic stimuli in ASIC3 knockout mice but detected no alterations in hypersensitivity after capsaicin or carrageenan treatment. In transgenic mice overexpressing a dominant-negative form of ASIC3, it has been shown that the response to thermal stimuli was normal, but the animals showed an increased response to intraperitoneal acid injection and mechanical hypersensitivity after inflammatory stimuli (52). There has been no satisfactory explanation for these discrepancies so far.…”

“…Possible causes are the variability in genetic background or species, differences in testing paradigms, environmental variability, and other compensatory effects. For example, Mogil et al (52) reported an elevated function of transient receptor potential vanilloid type 1 (TRPV1) channels in ASIC3-deficient mice. This increased TRPV1 activity may contribute to the observed hypersensitivity to painful stimuli in mice with impaired ASIC3 function.…”