Myogenic and neurogenic mechanisms underlying human colonic motility

      Background. Colonic contractile patterns are the result of the interplay of spontaneous pacemaker currents and the enteric nervous system (ENS). Aim. To describe the motility patterns displayed by human colonic strips in vitro and to summarize the adequate parameters to study enteric neurotransmission. Methods. We collected mechanical data from 15 patients (54 circularly-oriented strips, sigmoid colon). Results. All strips displayed rhythmic phasic contractions (RPCs) at 2.9 ± 0.3 c.p.m. RPCs appeared together with high-amplitude contractions at 0.13 ± 0.02 c.p.m in 30% of the preparations. Another 30% displayed a pattern in which RPCs waxed and waned their amplitude with a frequency of 0.28 ± 0.03 c.p.m. probably leading to segmentation. Modulation of slow wave amplitude by the second pacemaker could be the underlying mechanism of this pattern. Storage of colonic contents is accomplished by a nitric oxide (NO)-mediated sustained inhibition of contractile activity. Non-adrenergic, non-cholinergic conditions are needed to study inhibitory neurotransmission. L-NNA or MRS2500 should be used to further isolate purinergic or nitrergic responses respectively. Purinergic responses are dominant at low frequencies of EFS (>1 Hz) or short bursts while high frequencies are needed to release NO (>1 Hz). Excitatory neurotransmission should be characterized under non-nitrergic, non-purinergic conditions. The duration of the neuronal burst might determine if the response is mainly cholinergic (1 s) or if it also involves the release of tachykinins (10 s). Conclusion. RPCs, high-amplitude contractions and wax and wane are the main motility patterns displayed by human colonic strips. The ENS can be involved the origin, development and/or modulation of motility patterns and generation of contractions and relaxations.
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