Deletion of P2X2 and P2X3 receptor subunits does not alter motility of the mouse colon

Abstract

Purinergic P2X receptors contribute to neurotransmission in the gut. P2X receptors are ligand-gated cation channels that mediate synaptic excitation in subsets of enteric neurons. The present study evaluated colonic motility in vitro and in vivo in wild type (WT) and P2X2 and P2X3 subunit knockout (KO) mice. The muscarinic receptor agonist, bethanechol (0.3–3 μM), caused similar contractions of the longitudinal muscle in colon segments from WT, P2X2 and P2X3 subunit KO mice. Nicotine (1–300 μM), acting at neuronal nicotinic receptors, caused similar longitudinal muscle relaxations in colonic segments from WT and P2X2 and P2X3 subunit KO mice. Nicotine-induced relaxations were inhibited by nitro-l-arginine (NLA, 100 μM) and apamin (0.1 μM) which block inhibitory neuromuscular transmission. ATP (1–1000 μM) caused contractions only in the presence of NLA and apamin. ATP-induced contractions were similar in colon segments from WT, P2X2 and P2X3 KO mice. The mouse colon generates spontaneous migrating motor complexes (MMCs) in vitro. The MMC frequency was higher in P2X2 KO compared to WT tissues; other parameters of the MMC were similar in colon segments from WT, P2X2 and P2X3 KO mice. 5-Hydroxytryptophan-induced fecal output was similar in WT, P2X2 and P2X3 KO mice. These data indicate that nicotinic receptors are located predominately on inhibitory motor neurons supplying the longitudinal muscle in the mouse colon. P2X2 or P2X3 subunit containing receptors are not localized to motor neurons supplying the longitudinal muscle. Synaptic transmission mediated by P2X2 or P2X3 subunit containing receptors is not required for propulsive motility in the mouse colon.

Impaired propulsive motility in the distal but not proximal colon of BK channel β1‐subunit knockout mice

“…During the entire experiment, resting tension was monitored and the Krebs buffer solution was changed every 20 min. Frequency, amplitude, and duration of CMMCs were measured as described previously 20 . Propagated CMMCs were determined as a complex in which a contraction occurred first at the oral recording site followed by a contraction at the anal site.…”

“…Propagated CMMCs were determined as a complex in which a contraction occurred first at the oral recording site followed by a contraction at the anal site. Contractions propagated between the two recording sites at a velocity of ∼2 mm sec −1 20 . Retrogradely propagated contractions (anal to oral) were identified as those complexes in which a contraction occurred first at the anal recording site and after several seconds, a contraction occurred at the oral recording site.…”

“…Preparation of colonic segments for recordings of the Colonic Migrating Motor Complex (CMMC) was performed as described previously. 20 Briefly, the entire colon was removed from euthanized mice and placed into Krebs buffer solution. Luminal contents were gently flushed out with Krebs buffer solution.…”

“…Frequency, amplitude, and duration of CMMCs were measured as described previously. 20 Propagated CMMCs were determined as a complex in which a contraction occurred first at the oral recording site followed by a contraction at the anal site. Contractions propagated between the two recording sites at a velocity of 2 mm sec )1 .…”

Purinergic signalling in the enteric nervous system (An overview of current perspectives)

“…Heteromeric P2X2/3, P2X2/5 and P2X2/6 receptors have been functionally characterised in heterologous expression systems and in some native tissues, and also may be present in the ENS (Compan et al, 2012;Hausmann et al, 2012). Purinergic signalling still occurs in the ENS, without serious impairment of gastrointestinal motility, after gene deletion for P2X2 and P2X3 subunit proteins Ren et al, 2003;Devries et al, 2010).…”