Effects of acetylcholine on sling and clasp fibers of the human lower esophageal sphincter

A study on the congruence and proximity of the sling and clasp fibres at the cardio-esophageal junction of the stomach

BACKGROUND AND AIM

The cardio-oesophageal sphincter that is located in close longitudinal proximity to the origin of the lesser curvature of the stomach has a unique pattern of external muscle fibres whose inner oblique layer would normally form an elongated sling and the middle partially circular layer would form a projecting clasp into the already existing muscular sling of the former congruently, which would result in the formation of an anatomical sphincter in that area that would normally be devoid of the external longitudinal muscle layer coat. Certain authors have disagreed with the notion of this standard literature and have proposed that the clasp and sling fibres need not necessarily be congruent and may even remain independent of each other with partial contributions from the longitudinal muscle layers as well that may arise tangentially in different populations, which may in turn contribute to reflux oesophagitis in that population. Hence, the clasp and sling fibre muscular patterns were observed in six formalin-embalmed cadavers at the department of anatomy in a tertiary care institute as part of routine dissections in series, and the findings were then reported.

FINDINGS

At the junction of the lesser curvature of the stomach with the oesophagus, all six cadavers showed a longitudinal sling pattern as opposed to the conventional oblique sling. The circular muscle layer was found to be merged with the outer longitudinal muscle layer to form the sling that pulled away from the clasp, resulting in a loss of congruency for the same. The clasp fibres, however, were found to be contributed by the inner oblique muscle layer. The conventional perpendicular or tangential merging of the clasp with the sling was not observed; instead, an obtuse, blunt angular merging of the clasp with the sling was observed.

DISCUSSION

The deviation of the sling from the clasp could indicate a lack of a proper fit between them at the cardio-oesophageal sphincter. The lack of robustness in the attachment of the clasp to the sling may possibly contribute to the diminished taut pull of the clasp in this subset of the population. These would be significant determinants for a predisposition to reflux oesophagitis and Barrett's oesophagus.

The contribution of lysophosphatidic acid receptors in the response of human lower esophageal sphincter under the electrical field stimulation

BACKGROUND

This study aims to identify the impact on the reaction while the clasp and sling fibers of the human lower esophageal sphincter are under the electrical field stimulation, by adding lysophosphatidic acid receptor subtypes antagonist.

METHODS

Between March 2018 to December 2018, muscle strips were isolated from 28 patients who underwent esophagectomy for mid-third esophageal carcinomas. Muscle tension measurement technique in vitro and electrical field stimulation were used to examine the effects of selective lysophosphatidic acid receptor antagonist on the clasp and sling fibers of human lower esophageal sphincter.

RESULTS

The optimal frequency of frequency-dependent relaxation in clasp fibers and contraction in sling fibers induced by electrical field stimulation is 64 Hz and 128 Hz respectively. The selective lysophosphatidic acid 1 and 3 receptor antagonist produced no significant difference in the frequency-dependent relaxation in clasp fibers and contraction in sling fibers induced by the electrical field stimulation (P > 0.05).

CONCLUSION

The electrical field stimulation induced a frequency-dependent relaxation in clasp fibers and contraction in sling fibers. The lysophosphatidic acid 1 and 3 receptors are not involved in the response of clasp and sling fibers of the human lower esophageal sphincter induced by the electrical field stimulation.

Effects of lysophosphatidic acid on sling and clasp fibers of the human lower esophageal sphincter

Background

This study aims to explore the role of lysophosphatidic acid receptors in the regulation mechanisms of contraction and relaxation of human lower esophageal sphincter.

Methods

Between July 2015 and March 2016, muscle strips were collected from a total of 30 patients (19 males, 11 females; mean age: 62±9.9 years; range, 52 to 68 years) who underwent an esophagectomy for mid-third esophageal carcinomas. The specimens were maintained in oxygenated Krebs solution. Muscle tension measurement technique in vitro was used to examine the effects of non-selective lysophosphatidic acid receptors agonists and antagonists, as well as selective lysophosphatidic acid receptors agonists on the clasp and sling fibers of human lower esophageal sphincter.

Results

The non-selective dopamine receptor agonist lysophosphatidic acid induced the contraction of the clasp and sling fibers of the human lower esophageal sphincter. The response induced by nonselective lysophosphatidic acid receptor agonist was inhibited completely by non-selective lysophosphatidic acid receptor antagonist. The selective lysophosphatidic acid 1 and 2 receptor agonist and the selective lysophosphatidic acid 3 receptor agonist induced a concentration-dependent contractile response of the clasp and sling fibers of the human lower esophageal sphincter. There was no significant difference in contraction rates between the clasp and sling fibers (p>0.05).

Conclusion

This study indicates that lysophosphatidic acid regulates the lower esophageal sphincter is through its receptor; the lysophosphatidic acid receptors may be involved in the contractile response of the human lower esophageal sphincter.

The effects of acetylcholine on intracellular calcium fluorescence in smooth muscle cells of human esophagogastric junction cultured in vitro

BACKGROUND

Most esophageal motility studies are based on animals. It is necessary to explore smooth muscle motility in the human esophagus. This study was undertaken to explore the feasibility of in vitro culture of smooth muscle cells (SMCs) from human esophagogastric junction (EGJ) and to determine changes of intracellular calcium (Ca²⁺ ) fluorescence ([Ca²⁺ ]_i ) in SMCs stimulated by acetylcholine (ACh).

METHODS

Primary cells of EGJ (Clasp, Sling, esophageal circular muscle (ECM), and longitudinal muscle (ELM)) were obtained by enzymatic digestion (ED) and explant culture with tissues (EC-T) from 9 upper esophageal carcinoma patients. Cells were cultured in smooth muscle cell medium (SMCM) and DMEM/F-12 medium containing 10% newborn bovine serum (10%-F12), respectively, and then identified by α-SMA staining. After incubation with 5 μM Fluo-3/am, the effect of 10^-6  mM ACh on [Ca²⁺ ]_i in Ca²⁺ -containing and Ca²⁺ -free buffers was evaluated by confocal microscopy.

RESULTS

Cultured cells from ED and EC-T were identified as SMCs by α-SMA with spindle surface and "hills and valleys" morphology. Cells cultured in 10%-F12 showed better morphology. The main characteristic of [Ca²⁺ ]_i in Clasp-, Sling- and ECM-SMCs was the release of intracellular Ca²⁺ stores; the main characteristic in ELM-SMCs was extracellular Ca²⁺ influx. However, these cells seemed not to rely on a unique Ca²⁺ activity, instead combining the two activities to maintain [Ca²⁺ ]_i .

CONCLUSIONS

It was feasible to culture human EGJ SMCs in vitro; moreover, Ach-induced changes of [Ca²⁺ ]_i in EGJ SMCs represent a complex interaction of intracellular Ca²⁺ release and extracellular Ca²⁺ influx.

Generation of Spontaneous Tone by Gastrointestinal Sphincters

An important feature of the gastrointestinal (GI) muscularis externa is its ability to generate phasic contractile activity. However, in some GI regions, a more sustained contraction, referred to as "tone," also occurs. Sphincters are muscles oriented in an annular manner that raise intraluminal pressure, thereby reducing or blocking the movement of luminal contents from one compartment to another. Spontaneous tone generation is often a feature of these muscles. Four distinct smooth muscle sphincters are present in the GI tract: the lower esophageal sphincter (LES), the pyloric sphincter (PS), the ileocecal sphincter (ICS), and the internal anal sphincter (IAS). This chapter examines how tone generation contributes to the functional behavior of these sphincters. Historically, tone was attributed to contractile activity arising directly from the properties of the smooth muscle cells. However, there is increasing evidence that interstitial cells of Cajal (ICC) play a significant role in tone generation in GI muscles. Indeed, ICC are present in each of the sphincters listed above. In this chapter, we explore various mechanisms that may contribute to tone generation in sphincters including: (1) summation of asynchronous phasic activity, (2) partial tetanus, (3) window current, and (4) myofilament sensitization. Importantly, the first two mechanisms involve tone generation through summation of phasic events. Thus, the historical distinction between "phasic" versus "tonic" smooth muscles in the GI tract requires revision. As described in this chapter, it is clear that the unique functional role of each sphincter in the GI tract is accompanied by a unique combination of contractile mechanisms.

Development and Application of a Functional Human Esophageal Mucosa Explant Platform to Eosinophilic Esophagitis

There is an increasing prevalence of esophageal diseases but intact human tissue platforms to study esophageal function, disease mechanisms, and the interactions between cell types in situ are lacking. To address this, we utilized full thickness human donor esophagi to create and validate the ex vivo function of mucosa and smooth muscle (n = 25). Explanted tissue was tested for contractile responses to carbachol and histamine. We then treated ex vivo human esophageal mucosa with a cytokine cocktail to closely mimic the Th2 and inflammatory milieu of eosinophilic esophagitis (EoE) and assessed alterations in smooth muscle and extracellular matrix function and stiffening. We found that full thickness human esophagus as well as the individual layers of circular and longitudinal muscularis propria developed tension in response to carbachol ex vivo and that mucosa demonstrated squamous cell differentiation. Treatment of mucosa with Th2 and fibrotic cytokines recapitulated the majority of the clinical Eosinophilic Esophagitis Diagnostic Profile (EDP) on fluidic transcriptional microarray. Transforming growth factor-beta-1 (TGFβ1) increased gene expression of fibronectin, smooth muscle actin, and phospholamban (p < 0.001). The EoE cocktail also increased stiffness and decreased mucosal compliance, akin to the functional alterations in EoE (p = 0.001). This work establishes a new, transcriptionally intact and physiologically functional human platform to model esophageal tissue responses in EoE.

Roles of Na+/Ca2+ exchanger 1 in digestive system physiology and pathophysiology

The Na⁺/Ca²⁺ exchanger (NCX) protein family is a part of the cation/Ca²⁺ exchanger superfamily and participates in the regulation of cellular Ca²⁺ homeostasis. NCX1, the most important subtype in the NCX family, is expressed widely in various organs and tissues in mammals and plays an especially important role in the physiological and pathological processes of nerves and the cardiovascular system. In the past few years, the function of NCX1 in the digestive system has received increasing attention; NCX1 not only participates in the healing process of gastric ulcer and gastric mucosal injury but also mediates the development of digestive cancer, acute pancreatitis, and intestinal absorption. This review aims to explore the roles of NCX1 in digestive system physiology and pathophysiology in order to guide clinical treatments.

Effects of remifentanil on esophageal and esophagogastric junction (EGJ) bolus transit in healthy volunteers using novel pressure-flow analysis

BACKGROUND

Remifentanil is associated with subjective dysphagia and an objective increase in aspiration risk. Studies of opioid effects have shown decreased lower esophageal sphincter relaxation. We assessed bolus transit through the esophagus and esophagogastric junction (EGJ) during remifentanil administration using objective pressure-flow analysis.

METHODS

Data from 11 healthy young participants (23±3 years, 7 M) were assessed for bolus flow through the esophagus and EGJ using high-resolution impedance manometry (Manoscan™, Sierra Scientific Instruments, Inc., LES Angeles, CA, USA) with 36 pressure and 18 impedance segments. Data were analyzed for esophageal pressure topography and pressure-flow analysis using custom Matlab analyses (Mathworks, Natick, USA). Paired t tests were performed with a P-value of < .05 regarded as significant.

KEY RESULTS

Duration of bolus flow through (remifentanil/R 3.0±0.3 vs baseline/B 5.0 ± 0.4 seconds; P < .001) and presence at the EGJ (R 5.1 ± 0.5 vs B 7.1 ± 0.5 seconds; P = .001) both decreased during remifentanil administration. Distal latency (R 5.2 ± 0.4 vs B 7.5 ± 0.2 seconds; P < .001) and distal esophageal distension-contraction latency (R 3.5 ± 0.1 vs B 4.7 ± 0.2 seconds; P < .001) were both reduced. Intrabolus pressures were increased in both the proximal (R 5.3 ± 0.9 vs B 2.6 ± 1.3 mm Hg; P = .01) and distal esophagus (R 8.6 ± 1.7 vs B 3.1 ± 0.8 mm Hg; P = .001). There was no evidence of increased esophageal bolus residue.

CONCLUSIONS AND INFERENCES

Remifentanil-induced effects were different for proximal and distal esophagus, with a reduced time for trans-sphincteric bolus flow at the EGJ, suggestive of central and peripheral μ-opioid agonism. There were no functional consequences in healthy subjects.

Normal and abnormal physiology, pharmacology, and anatomy of the gastroesophageal junction high-pressure zone

The high-pressure zone of the gastroesophageal junction acts as a multifunctional valve that comprises different groups of smooth muscles located in the distal esophagus and the proximal stomach, in addition to the extrinsic crural diaphragm, composed of skeletal muscle. In this review article, we evaluate the current literature with respect to human subjects, discussing the anatomic locations and physiologic and pharmacologic processes controlling these muscles. These muscles work individually and as a group to prevent reflux of gastric contents while allowing anterograde passage of food and liquid and retrograde passage of gas. We also reviewed new findings with respect to abnormalities that are permissive of reflux of gastric contents into the esophagus, which may lead to gastroesophageal reflux disease.

Mechanism of bombesin-induced tonic contraction of the porcine lower esophageal sphincter

Gastroesophageal reflux disease (GERD) is a disorder that is related to an incompetent lower esophageal sphincter (LES). Previous studies showed that bombesin could increase LES pressure in humans and opossums. The aim of the present study was to characterize the effects of bombesin on porcine LES contraction. We used the selective agonists, neuromedin B (NMB), gastrin-releasing peptide (GRP), and [D-Tyr⁶,Apa-4Cl¹¹,Phe¹³,Nle¹⁴]bombesin-(6-14) (DTACPN-BN), as well as receptor antagonists of bombesin receptor subtype 2 (BB₂), and 3 (BB₃) for ex vivo contraction studies. Atropine, nifedipine, tetrodotoxin, and ω-conotoxin GVIA were used to explore the agonist-induced LES contraction mechanism. Reverse transcription polymerase chain reaction and immunohistochemistry were applied to detect bombesin receptor expression. Our results indicate that GRP and DTACPN-BN, but not NMB, induced tonic contractions of the porcine LES in a dose-dependent manner, and the contractions were inhibited with selective BB₂ and BB₃ antagonists. The GRP-induced contraction is mainly caused by L-type Ca²⁺ channel-mediated Ca²⁺ influx. However, DTACPN-BN-induced contractions are associated with neuronal conduction. RT-PCR and immunohistochemistry revealed that BB₂ and BB₃ were expressed in the porcine LES. Bombesin-induced tonic contraction of the LES is mediated through BB₂ and BB₃. Bombesin, BB_2, and BB₃ agonists might have the potential to treat GERD.

Expression of serotonin receptors in human lower esophageal sphincter

Serotonin (5-HT) is a neurotransmitter and vasoactive amine that is involved in the regulation of a large number of physiological functions. The wide variety of 5-HT-mediated functions is due to the existence of different classes of serotonergic receptors in the mammalian gastrointestinal tract and nervous system. The aim of this study was to explore the expression of multiple types of 5-HT receptor (5-HT_1AR, 5-HT_2AR, 5-HT_3AR, 5-HT₄R, 5-HT_5AR, 5-HT₆R and 5-HT₇R) in sling and clasp fibers from the human lower esophageal sphincter (LES). Muscle strips of sling and clasp fibers from the LES were obtained from patients undergoing esophagogastrectomy, and circular muscle strips from the esophagus and stomach were used as controls. Reverse transcription-polymerase chain reaction (RT-PCR), quantitative PCR and western blotting were used to investigate the expression of the various 5-HT receptor types. Messenger RNA for all seven 5-HT receptor types was identified in the sling and clasp fibers of the LES. At the mRNA level, the expression levels were highest for 5-HT_3AR and 5-HT₄R, and lowest for 5-HT_5AR, 5-HT₆R and 5-HT₇R. At the protein level, the expression levels were highest for 5-HT_3AR and 5-HT₄R, followed by 5-HT_1AR and 5-HT_2AR; 5-HT₇R was also detected at a low level. The expression of 5-HT_5AR and 5-HT₆R proteins was not confirmed. The results indicate that a variety of 5-HT receptor types can be detected in the human LES and probably contribute to LES function.

Expression of lysophosphatidic acid receptors in the human lower esophageal sphincter

Lysophosphatidic acid (LPA) is a bioactive lipid that is involved in a variety of physiological and pathological processes occurring in the gastrointestinal tract. It acts via six distinct types of receptors, LPA1, LPA2, LPA3, LPA4, LPA5 and LPA6, which belong to the family of G protein-coupled receptors. The aim of the present study was to detect the expression of the LPA receptors in the human lower esophageal sphincter (LES). Quantitative polymerase chain reaction and western blotting were used to analyze the expression of LPA1-6 receptors in sling and clasp fibers from the human LES. The results showed that the protein and mRNA expression levels of various LPA receptors were significantly different. Specifically, the mRNA and protein expression levels of the LPA1 receptor were higher compared with those of the other receptors. The prevalence of the LPA1 receptor mRNA and protein indicates that the LPA1 receptor is likely to be involved in the regulation of human LES functions.

Expression of dopamine receptors in human lower esophageal sphincter

BACKGROUND AND AIM

Dopamine (DA) is considered to be an important modulator of enteric function. Recent experiments have suggested that DA receptors are widely expressed in animal gastrointestinal tract. The aim of this study was to explore the expression of DA receptors (D(1) R, D(2) R, D(3) R, D(4) R, D(5) R) in sling fibers and clasp fibers from the human lower esophageal sphincter (LES).

METHODS

Muscle strips of sling and clasp fibers from the LES were obtained from patients undergoing esophago-gastrectomy, and circular muscle strips from the esophagus and stomach were used as controls. Reverse transcription-polymerase chain reaction and western blotting were used to determine the expression of the five subtypes of DA receptors.

RESULTS

Messenger RNA and protein for three of five DA receptors were identified in the sling and clasp fibers of the LES. Expression was highest for D(1) R, then D(5) R and D(2) R in decreasing levels. D(3) R and D(4) R mRNA and protein were not identified in the muscle strips.

CONCLUSION

D(1) R, D(2) R, D(5) R can be detected in the human LES, and probably contribute to LES function. D(3) R and D(4) R are not expressed, and probably do not contribute to LES function in humans.