Combined genetic and pharmacological inhibition of TRPV1 and P2X3 attenuates colorectal hypersensitivity and afferent sensitization

Abstract

Kiyatkin ME, Feng B, Schwartz ES, Gebhart GF. Combined genetic and pharmacological inhibition of TRPV1 and P2X3 attenuates colorectal hypersensitivity and afferent sensitization. Am J Physiol Gastrointest Liver Physiol 305: G638 -G648, 2013. First published August 29, 2013; doi:10.1152/ajpgi.00180.2013.-The ligand-gated channels transient receptor potential vanilloid 1 (TRPV1) and P2X3 have been reported to facilitate colorectal afferent neuron sensitization, thus contributing to organ hypersensitivity and pain. In the present study, we hypothesized that TRPV1 and P2X3 cooperate to modulate colorectal nociception and afferent sensitivity. To test this hypothesis, we employed TRPV1-P2X3 double knockout (TPDKO) mice and channel-selective pharmacological antagonists and evaluated combined channel contributions to behavioral responses to colorectal distension (CRD) and afferent fiber responses to colorectal stretch. Baseline responses to CRD were unexpectedly greater in TPDKO compared with control mice, but zymosan-produced CRD hypersensitivity was absent in TPDKO mice. Relative to control mice, proportions of mechanosensitive and -insensitive pelvic nerve afferent classes were not different in TPDKO mice. Responses of mucosal and serosal class afferents to mechanical probing were unaffected, whereas responses of muscular (but not muscular/mucosal) afferents to stretch were significantly attenuated in TPDKO mice; sensitization of both muscular and muscular/mucosal afferents by inflammatory soup was also significantly attenuated. In pharmacological studies, the TRPV1 antagonist A889425 and P2X3 antagonist TNP-ATP, alone and in combination, applied onto stretch-sensitive afferent endings attenuated responses to stretch; combined antagonism produced greater attenuation. In the aggregate, these observations suggest that 1) genetic manipulation of TRPV1 and P2X3 leads to reduction in colorectal mechanosensation peripherally and compensatory changes and/or disinhibition of other channels centrally, 2) combined pharmacological antagonism produces more robust attenuation of mechanosensation peripherally than does antagonism of either channel alone, and 3) the relative importance of these channels appears to be enhanced in colorectal hypersensitivity. pelvic nerve; purinergic receptor; single fiber; transient receptor potential; visceral pain CHRONIC ABDOMINAL PAIN is a key feature of irritable bowel syndrome (IBS), which is prevalent, costly, and difficult to manage. An important contributor to pain in IBS is heightened perception of mechanical events in the bowel (i.e., hypersensitivity). Indeed, patients with IBS typically report greater pain and/or reduced response thresholds to rectal balloon distension than control subjects (3,24,28,34,46). Although central processes contribute to colorectal hypersensitivity, the driving force is increased afferent mechanosensitivity (i.e., sensitization). For example, intrarectal lidocaine reduces pain evoked by rectal distension in healthy subjects as well as ongoing pain and both vi...

Optogenetic activation of mechanically insensitive afferents in mouse colorectum reveals chemosensitivity

“…AHS was used in previous studies as a physiologically relevant stimulus because it recapitulates the common situation of carbohydrate malabsorption in the large intestine (21). The virtue of IS is its rapid onset and relative ease of wash out, leading to widespread use to assess afferent sensitization in visceral and cutaneous tissues (4,9,11,19,20,35). We documented previously and here as well that significant proportions of MIAs from C57BL/6 mice are AHS or IS sensitive.…”

“…MIAs that responded to optical stimulation were tested by sequential exposure of their afferent endings to an acidic hypertonic solution (AHS) and an inflammatory soup (IS), each of which has been used previously on colorectal afferent endings (7,8,12,20,21). Brass tubing of 1-cm high ϫ 4-mm square, which has been shown to be chemically inert to AHS, IS, and bile salts (BS), was placed over the receptive ending on the mucosal surface, the Krebs was solution removed, and 150 l of AHS solution were applied directly to the receptive ending for 5 min.…”

The nicotinic α6 subunit gene determines variability in chronic pain sensitivity via cross-inhibition of P2X2/3 receptors

“…Purinergic receptors are important pain processing molecules known to be expressed on nociceptive small diameter neurons in the DRG (46), with important roles having been demonstrated for P2X2/3 (23, 24, 47), P2X4 (48), and P2X7 (49). P2X2/3 receptors have been shown to contribute to multiple pain modalities, including inflammatory pain (23, 24, 47, 50), neuropathic pain (51), visceral pain (52), musculoskeletal pain (53), cancer pain (54), and migraine (55). Presumably the α6* nicotinic receptors interacting in the periphery with P2X2/3 receptors are activated endogenously by acetylcholine, which exists abundantly in mammals both neuronally and non-neuronally, for example in keratinocytes (56).…”

Trpv1

“…Here, TRPV1 antagonists inhibit capsaicin-induced increases in pelvic nerve discharge and intravesical pressure in rats and are able to suppress bladder overactivity induced by resiniferatoxin and acetic acid (Charrua et al 2009;Kitagawa et al 2013b). In addition, TRPV1 antagonists have been demonstrated to be effective in reducing colonic hypersensitivity in rodents (Kiyatkin et al 2013;Wiskur et al 2010). …”