Interpretation of fluctuation of transmural potential difference across the proximal small intestine

Transmural recordings of gastrointestinal electrical activity using a spatially-dense microelectrode array

Objective. High-resolution serosal recordings provide detailed information about the bioelectrical conduction patterns in the gastrointestinal (GI) tract. However, equivalent knowledge about the electrical activity through the GI tract wall remains largely unknown. This study aims to capture and quantify the bioelectrical activity across the wall of the GI tract.Approach. A needle-based microelectrode array was used to measure the bioelectrical activity across the GI wallin vivo. Quantitative and qualitative evaluations of transmural slow wave characteristics were carried out in comparison to the serosal slow wave features, through which the period, amplitude, and SNR metrics were quantified and statistically compared.Main results. Identical periods of 4.7 ± 0.3 s with amplitudes of 0.17 ± 0.04 mV versus 0.31 ± 0.1 mV and signal to noise ratios of 5.5 ± 1.3 dB versus 14.4 ± 1.1 dB were observed for transmural and serosal layers, respectively. Four different slow wave morphologies were observed across the transmural layers of the GI wall. Similar amplitudes were observed for all morphology types, and Type 1 and Type 2 were of the highest prevalence, dominating the outer and inner layers. Type 2 was exclusive to the middle layer while Type 4 was primarily observed in the middle layer as well.Significance. This study demonstrates the validity of new methodologies for measuring transmural slow wave activation in the GI wall and can now be applied to investigate the source and origin of GI dysrhythmias leading to dysmotility, and to validate novel therapeutics for GI health and disease.

Effects of intestinal secretagogues and distension on small bowel myoelectric activity in fasted and fed conscious dogs

1. Defined jejunal segments were perfused with solutions of bile salts and of ricinoleic acid during fasting and after feeding in two groups of conscious dogs, one with the segment in continuity, and the other with a Thirty-Vella loop. Myoelectric activity was recorded from chronically implanted electrodes on the jejunal segment and also from the proximal and distal in situ bowel.2. The results in both groups were identical. During fasting, migrating complexes were present in the segment, but were replaced by intermittent spike activity during chenodeoxycholate without and with ricinoleic acid perfusion. After food, when migrating complexes were replaced by intermittent spike activity, none of the solutions produced any consistent effect.3. In fasted animals, low levels of distension (15 mmHg) interrupted the migrating complexes in the segment and induced intermittent spike activity which was similar to that seen with the secretagogues. The migrating complexes in the main bowel continued during distension. In fed animals, spike activity increased in the segment during distension at 25 mmHg and decreased in the main bowel. In both groups, distension of the segment to pressures between 37.5 and 50 mmHg abolished spike activity both in the distended segment and the main bowel in fasted and fed states, and, in fasted dogs, migrating complexes were also abolished.4. These results demonstrate that the inhibitory intestino-intestinal reflex is mediated through extrinsic nerves and does not require an intact myenteric plexus, whereas the altered myoelectric activity induced by secretagogues is a local effect and does not spread to adjacent bowel through either intrinsic or extrinsic neural pathways. It seems likely that the local motor effect of secretagogues is a result of net secretion, producing distension to pressures below the threshold required to activate the intestino-intestinal reflex.

Correlation of variations in intraluminal pressure and potential differences in the perfused colen

To investigate the nature of variations in the large intestine potential differences, a continuous perfusion of isotonic saline was carried out in the colon of 14 rats. Intraluminal pressure and potential differences between the lumen and the peritoneal cavity were continuously and simultaneously recorded, while impedance of the system and respiration were also constantly monitored. To obtain a quantitative evaluation of the data, Fast Fouier Transform was performed on the signals and their derivatives which were auto- and cross-correlated. While there was no obvious relation between pressure and potential in the unperfused colon, there was clear visual qualirative evidence that, during steady state conditions of perfusion, an increase in intraluminal pressure was accompanied by a decrease in potential differences, while impedance of the recording system remained unchanged. Computer analysis disclosed four narrow ranges of stable frequencies for both pressure and potential. They were centred around 0-3, 1-75, 10-7, and 75 cycles per minute, the latter being synchronous with respiration. It is concluded that the variations of potential differences recorded during perfusion, a well-know phenomenon, are not electrical artefacts: the fast rhythm is probably induced by respiration, which increases intracolonic pressure and that, in turn, reduces the absolute value of potential differences, which remain negative mucosa versus serosa. The slower rhythms are synchronous for pressure and potential. Mechanisms responsible for the decrease in potential related to the increase in pressure remain unknown.

Automated high-speed analysis of gastrointestinal myoelectric activity

The value of myoelectric recording in the gastrointestinal tract has been limited by the difficulty of analyzing the prolonged recordings which are required to demonstrate integrated physiological activity. This problem has been solved by the use of a tape recording system with accelerated replay, originally developed for cardiac monitoring. Rapid replay not only reduces the time required for data retrieval but also increases the frequency of the recorded signals to allow electronic separation of fast and slow wave activity for on-line conversion into digital pulses suitable for computer analysis. The technique is illustrated by the analysis of an imperfect prolonged multichannel recording of cannine gastrointestinal myoelectric activity, demonstrating some of the possibilities for data analysis and error detection inherent in the system.

Relationship between changes in intraluminal pressure and transmural potential difference in the human and canine jejunum in vivo

Recordings of transmural potential difference (PD) across the jejunum of conscious man in situ are characterised by spontaneous fluctuations of up to 10 mV. In 25 of 31 subjects (comprising seven normal controls and 24 patients under investigation for malabsorption, six of whom had coeliac disease) we observed a clear association between these fluctuations and changes in intraluminal pressure recorded at the same site. The most frequent PD changes were associated with type III pressure waves. These consisted predominantly of large waver (3-1 +/- 0-1 mV; mean +/- SEM, n = 317) which reached maximal amplitude approximately 45 seconds after the pressure peak and had a duration of 120 +/- 3 s, but also included less frequent spikes (0-5 +/- 0-1 mV; n = 110) concurrent with the pressure wave with a duration of 5 +/- 1 s. Although by recording at two sites in the jejunum 10 cm apart we were able to demonstrate that type III pressure waves appeared to be propagated aborally at a median rate of 60 cm per minute, the apparent rates of propagation of the corresponding PD waves were much more variable. The largest PD changes (7-8 +/- 0-4 mV; n = 19), lasting several minutes, were found in association with runs of type I waves (basic rhythm) superimposed on a type III wave. Both pressure and PD activities were suppressed by intramuscular propantheline bromide. Intraluminal pilocarpine caused a transient rise in PD not always accompanied by a change in pressure. Distention of the jejunum by rapid injection of a bolus of isotonic sodium chloride produced a delayed rise in the PD which could be prevented by prior administration of propantheline bromide. Experiments using Thirty-Vella loops of proximal jejunum in conscious dogs confirmed the effect of jejunal distension on the PD and also demonstrated that spontaneous retching is preceded by an increase in the PD. Consideration of these results in conjunction with data from other workers suggests the hypothesis that the larger spontaneous fluctuations in transmural PD in the jejunum of conscious man are caused by changes in electrogenic secretion associated with intestinal motility and mediated by cholinergic mechanisms. The possible association of increased secretory activity with motility may have functions of lubrication as well as diluting and mixing the chyme for easier digestion and absorption.