Three-dimensional multi-field modelling of gastric arrhythmias and their effects on antral contractions

The contraction activation of smooth muscle in the stomach wall (SW) is coordinated by slow electrical waves. The interstitial cells of Cajal (ICC), specialised pacemaker cells, initiate and propagate these slow waves. By establishing an electrically coupled network, each ICC adjusts its intrinsic pacing frequency to a single dominant frequency, to be a key aspect in modelling the electrophysiology of gastric tissue. In terms of modelling, additional fields associated with electrical activation, such as voltage-dependent calcium influx and the resulting deformation, have hardly been considered so far. Here we present a three-dimensional model of the electro-chemomechanical activation of gastric smooth muscle contractions. To reduce computational costs, an adaptive multi-scale discretisation strategy for the temporal resolution of the electric field is used. The model incorporates a biophysically based model of gastric ICC pacemaker activity that aims to simulate stable entrainment and physiological conduction velocities of the electrical slow waves. Together with the simulation of concomitant gastric contractions and the inclusion of a mechanical feedback mechanism, the model is used to study dysrhythmias of gastric slow waves induced by abnormal stretching of the antral SW. The model is able to predict the formation of stretch-induced gastric arrhythmias, such as the emergence of an ectopic pacemaker in the gastric antrum. The results show that the ectopic event is accompanied by smooth muscle contraction and, although it disrupts the normal propagation pattern of gastric slow electrical waves, it can also catalyse the process of handling indigestible materials that might otherwise injure the gastric SW.

Relationships between serum electrolyte concentrations and ileus: A joint clinical and mathematical modeling study

Aim

Prolonged postoperative ileus (PPOI) occurs in around 15% of patients after major abdominal surgery, posing a significant clinical and economic burden. Significant fluid and electrolyte changes may occur peri‐operatively, potentially contributing to PPOI; however, this association has not been clearly elucidated. A joint clinical‐theoretical study was undertaken to evaluate peri‐operative electrolyte concentration trends, their association with ileus, and predicted impact on bioelectrical slow waves in interstitial cells of Cajal (ICC) and smooth muscle cells (SMC).

Methods

Data were prospectively collected from 327 patients undergoing elective colorectal surgery. Analyses were performed to determine associations between peri‐operative electrolyte concentrations and prolonged ileus. Biophysically based ICC and SMC mathematical models were adapted to evaluate the theoretical impacts of extracellular electrolyte concentrations on cellular function.

Results

Postoperative day (POD) 1 calcium and POD 3 chloride, sodium were lower in the PPOI group (p < 0.05), and POD3 potassium was higher in the PPOI group (p < 0.05). Deficits beyond the reference range in PPOI patients were most notable for sodium (Day 3: 29.5% ileus vs. 18.5% no ileus, p = 0.04). Models demonstrated an 8.6% reduction in slow‐wave frequency following the measured reduction in extracellular NaCl on POD5, with associated changes in cellular slow‐wave morphology and amplitude.

Conclusion

Low serum sodium and chloride concentrations are associated with PPOI. Electrolyte abnormalities are unlikely to be a primary mechanism of ileus, but their pronounced effects on cellular electrophysiology predicted by modeling suggest these abnormalities may adversely impact motility recovery. Resolution and correction of electrolyte abnormalities in ileus may be clinically relevant.

[Effects of Electroacupuncture on Ultrastructure of Interstitial Cells of Cajal and Stem Cell Factor-kit Signal Pathway of Gastric Antrum in Diabetic Gastroparesis Rats]

OBJECTIVE

To observe the effects of electroacupuncture (EA) on gastrointestinal motility and the ultrastructure of interstitial cells of Cajal (ICC) and the expressions of c-kit receptor protein and stem cell factor (SCF) mRNA in diabetic gastroparesis (DGP) rats, so as to explore its mechanism.

METHODS

Fifty SD rats were randomly divided into normal, model, acupoint, non-acupoint and metoclopramide groups (n＝10 rats/group). DGP model was established by intraperitoneal injection of streptozotocin (STZ, 2%), and raised with high-sugar high-fat diet irregularly. EA (sparse-dense, 10 Hz/50 Hz, 2 mA, 20 min) was applied at "Zusanli" (ST 36), "Liangmen" (ST 21) and "Sanyinjiao" (SP 6), and the corresponding non-acupoints of the 3 acupoints, daily for 15 days. The rats in metoclopramide group received intragastric administration of metoclopramide (1.7%, 1 mL/100 g) for 15 days, once a day. Blood sugar was determined with One Touch blood glucose test paper. The gastric emptying rate (GER) and the intestinal propulsion rate (IPR) were measured by intragastric phenol red. The ultrastructure of ICC was detected by transmission electron microscopy. The expression levels of c-kit receptor protein and SCF mRNA of gastric antrum were examined respectively by Western blot and RT-PCR.

RESULTS

Compared with the normal group, the blood glucose significantly increased in the model group (P<0.01), while the GER, IRP and the expression level of SCF mRNA in the gastric antrum significantly decreased (P<0.01), and the ultrastructure of ICC appeared apoptosis-like changes. The blood glucose of the EA group was obviously decreased compared with that of the model group (P<0.05); the GER and IRP significantly increased(P<0.05, P<0.01); the expression level of SCF mRNA increased (P<0.01), the number of ICC increased and its ultrastructure was repaired. There was some relief on ICC ultrastructure in the acupoint group compared with that in the non-acupoint group; and SCF mRNA increased (P<0.05). There was no significant difference on c-kit receptor expression among all the modeling groups (P＞0.05).

CONCLUSIONS

EA at ST 36, etc. can regulate the blood glucose and improve gastrointestinal emptying in DGP rats. The mechanism may be related to up-regulating SCF mRNA, repairing ICC ultrastructure, restoring the pacing function, and improving gastrointestinal motility.

Pituitary Adenylate Cyclase-activating Polypeptide Inhibits Pacemaker Activity of Colonic Interstitial Cells of Cajal

This study aimed to investigate the effect of pituitary adenylate cyclase-activating peptide (PACAP) on the pacemaker activity of interstitial cells of Cajal (ICC) in mouse colon and to identify the underlying mechanisms of PACAP action. Spontaneous pacemaker activity of colonic ICC and the effects of PACAP were studied using electrophysiological recordings. Exogenously applied PACAP induced hyperpolarization of the cell membrane and inhibited pacemaker frequency in a dose-dependent manner (from 0.1 nM to 100 nM). To investigate cyclic AMP (cAMP) involvement in the effects of PACAP on ICC, SQ-22536 (an inhibitor of adenylate cyclase) and cell-permeable 8-bromo-cAMP were used. SQ-22536 decreased the frequency of pacemaker potentials, and cell-permeable 8-bromo-cAMP increased the frequency of pacemaker potentials. The effects of SQ-22536 on pacemaker potential frequency and membrane hyperpolarization were rescued by co-treatment with glibenclamide (an ATP-sensitive K(+) channel blocker). However, neither N (G)-nitro-L-arginine methyl ester (L-NAME, a competitive inhibitor of NO synthase) nor 1H-[1,2,4]oxadiazolo[4,3-α]quinoxalin-1-one (ODQ, an inhibitor of guanylate cyclase) had any effect on PACAP-induced activity. In conclusion, this study describes the effects of PACAP on ICC in the mouse colon. PACAP inhibited the pacemaker activity of ICC by acting through ATP-sensitive K(+) channels. These results provide evidence of a physiological role for PACAP in regulating gastrointestinal (GI) motility through the modulation of ICC activity.

Interplay of hydrogen sulfide and nitric oxide on the pacemaker activity of interstitial cells of cajal from mouse small intestine

We studied whether nitric oxide (NO) and hydrogen sulfide (H(2)S) have an interaction on the pacemaker activities of interstitial cells of Cajal (ICC) from the mouse small intestine. The actions of NO and H(2)S on pacemaker activities were investigated by using the whole-cell patch-clamp technique and intracellular Ca(2+) analysis at 30℃ in cultured mouse ICC. Exogenously applied (±)-S-nitroso-N-acetylpenicillamine (SNAP), an NO donor, or sodium hydrogen sulfide (NaHS), a donor of H(2)S, showed no influence on pacemaker activity (potentials and currents) in ICC at low concentrations (10 µM SNAP and 100 µM NaHS), but SNAP or NaHS completely inhibited pacemaker amplitude and pacemaker frequency with increases in the resting currents in the outward direction at high concentrations (SNAP 100 µM and NaHS 1 mM). Co-treatment with 10 µM SNAP plus 100 µM NaHS also inhibited pacemaker amplitude and pacemaker frequency with increases in the resting currents in the outward direction. ODQ, a guanylate cyclase inhibitor, or glibenclamide, an ATP-sensitive K(+) channel inhibitor, blocked the SNAP+NaHS-induced inhibition of pacemaker currents in ICC. Also, we found that SNAP+NaHS inhibited the spontaneous intracellular Ca(2+) ([Ca(2+)](i)) oscillations in cultured ICC. In conclusion, this study describes the enhanced inhibitory effects of NO plus H(2)S on ICC in the mouse small intestine. NO+H(2)S inhibited the pacemaker activity of ICC by modulating intracellular Ca(2+). These results may be evidence of a physiological interaction of NO and H(2)S in ICC for modulating gastrointestinal motility.

5-hydroxytryptamine generates tonic inward currents on pacemaker activity of interstitial cells of cajal from mouse small intestine

In this study we determined whether or not 5-hydroxytryptamine (5-HT) has an effect on the pacemaker activities of interstitial cells of Cajal (ICC) from the mouse small intestine. The actions of 5-HT on pacemaker activities were investigated using a whole-cell patch-clamp technique, intracellular Ca(2+) ([Ca(2+)](i)) analysis, and RT-PCR in ICC. Exogenously-treated 5-HT showed tonic inward currents on pacemaker currents in ICC under the voltage-clamp mode in a dose-dependent manner. Based on RT-PCR results, we found the existence of 5-HT(2B, 3, 4, and 7) receptors in ICC. However, SDZ 205557 (a 5-HT(4) receptor antagonist), SB 269970 (a 5-HT7 receptor antagonist), 3-tropanylindole - 3 - carboxylate methiodide (3-TCM; a 5-HT(3) antagonist) blocked the 5-HT-induced action on pacemaker activity, but not SB 204741 (a 5-HT(2B) receptor antagonist). Based on [Ca(2+)](i) analysis, we found that 5-HT increased the intensity of [Ca(2+)](i). The treatment of PD 98059 or JNK II inhibitor blocked the 5-HT-induced action on pacemaker activity of ICC, but not SB 203580. In summary, these results suggest that 5-HT can modulate pacemaker activity through 5-HT(3, 4, and 7) receptors via [Ca(2+)](i) mobilization and regulation of mitogen-activated protein kinases.

Regional Distribution of Interstitial Cells of Cajal (ICC) in Human Stomach

We elucidated the distribution of interstitial cells of Cajal (ICC) in human stomach, using cryosection and c-Kit immunohistochemistry to identify c-Kit positive ICC. Before c-Kit staining, we routinely used hematoxylin and eosin (HE) staining to identify every structure of human stomach, from mucosa to longitudinal muscle. HE staining revealed that the fundus greater curvature (GC) had prominent oblique muscle layer, and c-Kit immunostaining c-Kit positive ICC cells were found to have typical morphology of dense fusiform cell body with multiple processes protruding from the central cell body. In particular, we could observe dense processes and ramifications of ICC in myenteric area and longitudinal muscle layer of corpus GC. Interestingly, c-Kit positive ICC-like cells which had morphology very similar to ICC were found in gastric mucosa. We could not find any significant difference in the distribution of ICC between fundus and corpus, except for submucosa where the density of ICC was much higher in gastric fundus than corpus. Furthermore, there was no significant difference in the density of ICC between each area of fundus and corpus, except for muscularis mucosa. Finally, we also found similar distribution of ICC in normal and cancerous tissue obtained from a patient who underwent pancreotomy and gastrectomy. In conclusion, ICC was found ubiquitously in human stomach and the density of ICC was significantly lower in the muscularis mucosa of both fundus/corpus and higher in the submucosa of gastric fundus than corpus.

The inhibitory effects of hydrogen sulfide on pacemaker activity of interstitial cells of cajal from mouse small intestine

In this study, we studied whether hydrogen sulfide (H(2)S) has an effect on the pacemaker activity of interstitial cells of Cajal (ICC), in the small intestine of mice. The actions of H(2)S on pacemaker activity were investigated using whole-cell patch-clamp technique, intracellular Ca(2+) analysis at 30 and RT-PCR in cultured mouse intestinal ICC. Exogenously applied sodium hydrogen sulfide (NaHS), a donor of hydrogen sulfide, caused a slight tonic inward current on pacemaker activity in ICC at low concentrations (50 and 100 microM), but at high concentration (500 microM and 1 mM) it seemed to cause light tonic inward currents and then inhibited pacemaker amplitude and pacemaker frequency, and also an increase in the resting currents in the outward direction. Glibenclamide or other potassium channel blockers (TEA, BaCl(2), apamin or 4-aminopydirine) did not have an effect on NaHS-induced action in ICC. The exogenous application of carbonilcyanide p-triflouromethoxyphenylhydrazone (FCCP) and thapsigargin also inhibited the pacemaker activity of ICC as NaHS. Also, we found NaHS inhibited the spontaneous intracellular Ca(2+) ([Ca(2+)](i)) oscillations in cultured ICC. In doing an RT-PCR experiment, we found that ICC enriched population lacked mRNA for both CSE and CBS, but was prominently detected in unsorted muscle. In conclusion, H(2)S inhibited the pacemaker activity of ICC by modulating intracellular Ca(2+). These results can serve as evidence of the physiological action of H(2)S as acting on the ICC in gastrointestinal (GI) motility.

Voltage-dependent Ca Current Identified in Freshly Isolated Interstitial Cells of Cajal (ICC) of Guinea-pig Stomach

The properties of voltage dependent Ca(2+) current (VDCC) were investigated in interstitial cells of Cajal (ICC) distributed in the myenteric layer (ICC-MY) of guinea-pig antrum. In tissue, ICC-MY showed c-Kit positive reactions and produced driving potentials with the amplitude and frequency of about 62 mV and 2 times min(-1), respectively, in the presence of 1 microM nifedipine. Single ICC-MY isolated by enzyme treatment also showed c-Kit immunohistochemical reactivity. These cells were also identified by generation of spontaneous inward current under K(+) -rich pipette solution. The voltage clamp experiments revealed the amplitude of - 329 pA inward current at irregular frequency. With Cs(+)-rich pipette solution at V(h)=-80 mV, ICC-MY produced voltage-dependent inward currents (VDIC), and nifedipine (1 microM) blocked VDIC. Therefore, we successfully isolated c-Kit positive single ICC from guinea-pig stomach, and found that ICC-MY potently produced dihydropiridine sensitive L-type voltage-dependent Ca(2+) currents (VDCC(L)).

(-)-epigallocatechin gallate inhibits the pacemaker activity of interstitial cells of cajal of mouse small intestine

The effects of (-)-epigallocatechin gallate (EGCG) on pacemaker activities of cultured interstitial cells of Cajal (ICC) from murine small intestine were investigated using whole-cell patch-clamp technique at 30 and Ca(2+) image analysis. ICC generated spontaneous pacemaker currents at a holding potential of -70 mV. The treatment of ICC with EGCG resulted in a dose-dependent decrease in the frequency and amplitude of pacemaker currents. SQ-22536, an adenylate cyclase inhibitor, and ODQ, a guanylate cyclase inhibitor, did not inhibit the effects of EGCG. EGCG-induced effects on pacemaker currents were not inhibited by glibenclamide, an ATP-sensitive K(+) channel blocker and TEA, a Ca(2+)-activated K(+) channel blocker. Also, we found that EGCG inhibited the spontaneous [Ca(2+)](i) oscillations in cultured ICC. In conclusion, EGCG inhibited the pacemaker activity of ICC and reduced [Ca(2+)](i) oscillations by cAMP-, cGMP-, ATP-sensitive K+ channel-independent manner.

Involvement of thromboxane a(2) in the modulation of pacemaker activity of interstitial cells of cajal of mouse intestine

Although many studies show that thromboxane A(2) (TXA(2)) has the action of gastrointestinal (GI) motility using GI muscle cells and tissue, there are no reports on the effects of TXA(2) on interstitial cells of Cajal (ICC) that function as pacemaker cells in GI tract. So, we studied the modulation of pacemaker activities by TXA(2) in ICC with whole cell patch-clamp technique. Externally applied TXA(2) (5microM) produced membrane depolarization in current-clamp mode and increased tonic inward pacemaker currents in voltage-clamp mode. The tonic inward currents by TXA(2) were inhibited by intracellular application of GDP-beta-S. The pretreatment of ICC with Ca(2+) free solution and thapsigargin, a Ca(2+)-ATPase inhibitor in endoplasmic reticulum, abolished the generation of pacemaker currents and suppressed the TXA(2)-induced tonic inward currents. However, chelerythrine or calphostin C, protein kinase C inhibitors, did not block the TXA(2)-induced effects on pacemaker currents. These results suggest that TXA(2) can regulate intestinal motility through the modulation of ICC pacemaker activities. This modulation of pacemaker activities by TXA(2) may occur by the activation of G protein and PKC independent pathway via extra and intracellular Ca(2+) modulation.