Substance P activates a non-selective cation channel in murine pacemaker ICC

Abstract  Interstitial cells of Cajal (ICC) associated with Auerbach's plexus in the small intestine, provide pacemaker activity to orchestrate peristalsis and mixing. Despite the close apposition between ICC and enteric nerves, little is known about the neural regulation of pacemaker activity. The present study pursues the hypothesis that substance P can affect pacemaker activity through action on non-selective cation channels. Cell-attached and inside-out patch clamp studies were performed on isolated ICC in short-term cultures that provided evidence that substance P increases open probability or initiates activity in non-selective cation channels in ICC. The single-channel conductance is ∼25 pS and in the on-cell configuration the activity can occur in a rhythmic fashion. Patches contained 1–10 channels and were most often accompanied by a ∼12 pS chloride channel that was also activated by substance P. In a recently developed preparation that allows patch clamping in ICC in their natural environment within tissue, i.e. in situ , the presence of the channel and substance P activation was confirmed. The non-selective cation channel is one of the channels that initiate intestinal pacemaker activity and the present study provides further single-channel data on this critical channel. Because of the close proximity of enteric motor and sensory nerves to ICC, these data provide a potential mechanism underlying neural regulation of pacemaker activity. The data also indicate that neurokinergic pharmacology is a promising avenue for excitation of the intestinal pacemaker system.     

Salvinorin A inhibits colonic transit and neurogenic ion transport in mice by activating κ-opioid and cannabinoid receptors

Abstract  The major active ingredient of the plant Salvia divinorum , salvinorin A (SA) has been used to treat gastrointestinal (GI) symptoms. As the action of SA on the regulation of colonic function is unknown, our aim was to examine the effects of SA on mouse colonic motility and secretion in vitro and in vivo . The effects of SA on GI motility were studied using isolated preparations of colon, which were compared with preparations from stomach and ileum. Colonic epithelial ion transport was evaluated using Ussing chambers. Additionally, we studied GI motility in vivo by measuring colonic propulsion, gastric emptying, and upper GI transit. Salvinorin A inhibited contractions of the mouse colon, stomach, and ileum in vitro , prolonged colonic propulsion and slowed upper GI transit in vivo . Salvinorin A had no effect on gastric emptying in vivo . Salvinorin A reduced veratridine-, but not forskolin-induced epithelial ion transport. The effects of SA on colonic motility in vitro were mediated by κ-opioid receptors (KORs) and cannabinoid (CB) receptors, as they were inhibited by the antagonists nor-binaltorphimine (KOR), AM 251 (CB₁ receptor) and AM 630 (CB₂ receptor). However, in the colon in vivo , the effects were largely mediated by KORs. The effects of SA on veratridine-mediated epithelial ion transport were inhibited by nor-binaltorphimine and AM 630. Salvinorin A slows colonic motility in vitro and in vivo and influences neurogenic ion transport. Due to its specific regional action, SA or its derivatives may be useful drugs in the treatment of lower GI disorders associated with increased GI transit and diarrhoea.     

Validation of a semi-automated scintigraphic technique for detecting episodic, real-time colonic flow

The relationships between the movement of colonic content and regional pressures have only been partially defined. During the analysis of a combined colonic scintigraphic and manometric study, a quantitative technique for determining discrete, episodic, real-time colonic flow was developed. Our aim was to validate this technique through the construction of a computer-generated phantom model of known antegrade and retrograde motility. The anthropoid phantom was rasterized into a 6-mm voxel model to create a 3D voxel phantom of the colon with four distinct colonic segments. Associating a time/activity curve with each segment simulated dynamic behaviour. Activity in the model was based on data obtained from human colonic scintigraphic recordings using 30 MBq of (99m)Tc sulphur colloid. The flow was simulated by modifying the input time/activity functions to represent episodes of net flow of 2%, 5% or 10% of segmental content. Our quantitative technique was applied to the phantom model to measure the accuracy with which simulated flows were detected. Our quantitative technique proved to be a sensitive and specific means of detecting the presence and the magnitude of discrete episodes of colonic flow and therefore, should improve our ability to correlate colonic flow and motor patterns.