Modelling Human Colonic Smooth Muscle Cell Electrophysiology

Electrophysiological modeling of the effect of potassium channel blockers on the distribution of stimulation wave in the human gastric wall cells

The purpose of this study is to model the electrophysiological behavior of excitable membrane and wavefront propagation in the Stomach Wall in physiological and pharmacological states. The propagation of this wave is based on cellular electrophysiological activity and ionic channel properties. In this study, we arranged the stomach wall cells together using the Gap Junctions approach. Slow wave is generated by gastric pacemaker cells. This wave propagates via the interaction of cells with each other throughout the stomach wall. Potassium currents are one of the main factors in regulating the pattern of wavefront propagation. To investigate the effect of limiting the exchange of potassium currents from cell membranes, 10%, 50%, 90%, and complete blockade were applied on both non-inactivating potassium current (I_Kni) and fast-inactivating potassium current (I_Kfi). The results show that I_Kniion channel blockage has a considerable effect on the plateau phase in the propagation of the excitation wave. The maximum value of the action potential in the plateau phase in the excitation wave with complete obstruction from -40.92 mV in the physiological state reached -18.97 mV, which is about 54% higher than the physiological state. Also, compared to the physiological state, complete blockage of the I_Kfi causes a 15% increase in the slow-wave spike phase (from -36.72 mV to -31.36 mV). Using this model, the effect of ions in different phases of slow-wave can be investigated. In addition, by blocking ion channels, functional disorders and smooth muscle contraction can be improved.

Manometric recordings bring out post-stimulus refractory states in the anal canal in neonates

Anorectal manometry is a diagnostic technique used to investigate the correct mechanical performance of the internal anal sphincter (IAS). By distending the rectal ampulla while recording changes in the luminal pressure, this method allows for characterizing the anorectal reflex. It can also provide, indirectly, information about the electrical activity of the IAS. In this study, seventeen neonates having 24-hour delayed passage of meconium or presenting distal intestinal obstruction symptoms underwent anorectal manometry to discard Hirschsprung's disease. All patients had normal anorectal reflex. The time delay between stimulation of the rectal ampulla and the relaxation of the anal canal was studied. The average period of the pressure fluctuations was 5.44 ± 0.13s. The overall duration of the relaxation time was 9.71 ± 0.21s. The maximum lag between the onset of the stimulus and the relaxation of the IAS was 2.90 s, and was achieved when the stimulus was applied following a local maximum of the pressure wave. The existence of a refractory period during the suprathreshold depolarization of smooth muscle cells can explain the evidence of a temporal delay between the stimulus and the mechanical response. In occasions, relaxation appeared first distally. This phenomenon can be explained by the arrangement and morphology of bipolar cells, which may evidence the anisotropic propagation of the mechanical activity. These data may contribute to depict the alterations in excitability underlying the relaxation reflex by means of manometric recording of the anal canal.

Computational motility models of neurogastroenterology and neuromodulation

The success of neuromodulation therapies, particularly in the brain, spinal cord, and peripheral nerves, has been greatly aided by computational, biophysical models. However, treating gastrointestinal disorders with electrical stimulation has been much less explored, partly because the mode of action of such treatments is unclear, and selection of stimulation parameters is often empirical. Progress in gut neuromodulation is limited by the comparative lack of biophysical models capable of simulating neuromodulation of gastrointestinal function. Here, we review the recently developed biophysical models of electrically-active cells in the gastrointestinal system that contribute to motility. Biophysical models are replacing phenomenologically-defined models due to advancements in electrophysiological characterization of key players in the gut: enteric neurons, smooth muscle fibers, and interstitial cells of Cajal. In this review, we explore existing biophysically-defined cellular and network models that contribute to gastrointestinal motility. We focus on recent models that are laying the groundwork for modeling electrical stimulation of the gastrointestinal system. Developing models of gut neuromodulation will improve our mechanistic understanding of these treatments, leading to better parameterization, selectivity, and efficacy of neuromodulation to treat gastrointestinal disorders. Such models may have direct clinical translation to current neuromodulation therapies, such as sacral nerve stimulation.

Progress in Mathematical Modeling of Gastrointestinal Slow Wave Abnormalities

Gastrointestinal (GI) motility is regulated in part by electrophysiological events called slow waves, which are generated by the interstitial cells of Cajal (ICC). Slow waves propagate by a process of "entrainment," which occurs over a decreasing gradient of intrinsic frequencies in the antegrade direction across much of the GI tract. Abnormal initiation and conduction of slow waves have been demonstrated in, and linked to, a number of GI motility disorders. A range of mathematical models have been developed to study abnormal slow waves and applied to propose novel methods for non-invasive detection and therapy. This review provides a general outline of GI slow wave abnormalities and their recent classification using multi-electrode (high-resolution) mapping methods, with a particular emphasis on the spatial patterns of these abnormal activities. The recently-developed mathematical models are introduced in order of their biophysical scale from cellular to whole-organ levels. The modeling techniques, main findings from the simulations, and potential future directions arising from notable studies are discussed.