Non-peristaltic patterns of motor activity in the guinea-pig proximal colon

Background The guinea-pig proximal colon contains semi-solid feces which are propelled by intermittent neural peristaltic waves to the distal colon, where solid pellets are formed. Between propulsive periods, complex motor patterns underlie fluid re-absorption and mixing of contents. Methods Spatio-temporal analysis of video recordings were used to investigate neural and myogenic patterns of non-peristaltic motor activity. Key Results At low distension (6 cmH(2)O), two major motor patterns were seen. Narrow rings of constriction (abrupt contractions) occurred at 19 cpm. These previously undescribed contractions occurred, almost simultaneously, at many points along the preparation, with a calculated propagation velocity of 110 mm s-1. They were abolished by hexamethonium and by tetrodotoxin, indicating they were neurally mediated. Inhibition of nitric oxide synthase resulted in increased frequency of 'abrupt contractions' suggesting ongoing inhibitory modulation by endogenous nitric oxide. After tetrodotoxin, another distinct motor pattern was revealed; 'ripples'1 consisted of shallow rings of contraction, occurring at 18 cpm and propagating at 2.7-2.9 mm s-1 orally or aborally from multiple initiation sites. The frequency of 'ripples' increased as intraluminal pressure was raised, becoming very irregular at high distensions. L-type calcium channel blockers and openers affected the amplitude of 'ripples'. No frequency gradient of 'ripples' along the proximal colon was detected. This absence explains the multiple initiation sites which often shifted over time, and the oral and aboral propagation of 'ripples'. Conclusions & Inferences The interaction of myogenic 'ripples' with neurogenic 'abrupt contractions' generates localized alternating rings of contractions and dilatation, well suited to effective mixing of contents.