Characterization of Ascending Limb of Peristaltic Reflex in Distal Colon of W/W V Wild Type and Mutant Mice

Abstract

Background: Ascending neuromuscular reflexes induced by distension play an important role in gastrointestinal motility. However, the mechanisms underlying this reflex in colon is incompletely understood. AIM: To investigate nerve stimulation and balloon distention (BD)-mediated ascending responses in circular and longitudinal smooth muscle (CSM; LSM) of murine distal colon. METHODS: Conventional intracellular recordings were performed in colonic LSM and CSM fromW/Wvwild-type and CSM fromW/Wvmutant mice. Responses to nerve stimulation (NS; 4 square wave pulses, each 0.3 ms duration, 20 Hz) and BD (0.1 ml, 10 s) were measured in proximal end of a ~ 1.5 cm segment of distal colon. A balloon was placed in the lumen of distal end and a pair of transmural NS electrodes were positioned between the balloon and recording sites. Tissue preparations were perfused with Krebs' solution at 36oC. RESULTS: In the CSM, NS evoked mono-phasic inhibitory junction potentials (IJP) with amplitude of 35.4 ± 1.8 mV and duration of 795 ± 39 ms, and BD induced depolarization of 5.7 ± 1.8 mV (n = 5) that reached a peak in 4 7 s and was maintained until the termination of the BD. Spontaneous action potentials (APs) were superimposed on the depolarization. Application of atropine (3 μM) to the bath significantly increased the NS-induced IJP from 35.4 ± 1.8 mV to 38.5 ± 1.8 mV, but abolished the BDinduced depolarization. In the LSM, NS produced a biphasic IJP; a fast IJP with amplitude of 22.7 ± 1.6 mV and duration of 1071 ± 42 ms, following by a slow IJP (sIJP) with amplitude of 4.6 ± 1.3 mV and duration of 3236 ± 370 ms (n = 3). BD evoked an initial IJP with amplitude of 4.8 ± 3.8 mV and duration of 489 ± 128 ms, following by a train of APs. MRS-2500 (1 μM), a P2Y1 antagonist, abolished the initial IJP, whereas atropine abolished the APs. In CSM from W/Wv mutant mice, responses to NS were no different from controls. However, the depolarization in response to BD was attenuated and delayed in onset until after the balloon was deflated. CONCLUSIONS: These data indicate that in the murine distal colon: 1) Ascending response induced by BD differs from that induced by the NS; 2) Ascending response evoked by the BD in CSM differs from LSM; 3) Only cholinergic nerves are involved in ascending excitation to both CSM and LSM; 4. Ascending BD, but not NS, responses are impaired in W/Wv mutant mice, suggesting that ICCs may be involved in transducing the BD response.