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ents of the HPZ. From prior anatomic studies using simultaneous high resolution manometry and high frequency ultrasound with pharmacologic manipulation, these HPZ components represent a proximal lower esophageal circular muscle sphincter (LEC), a mid crural diaphragm (CD) and a distal gastric sling and clasp muscle fiber complex. The average pressure in each of these components was 24.7+/10.7mmHg in the LEC, 33.2+/-17.2mmHg in the crural diaphragm and 15.83+/-8.03 in the clasp sling muscle fiber complex. The width of the LEC, crural diaphragm and gastric sling clasp fiber complex was 1.01 +/0.25cm, 1.29 +/0.37cm and 0.76 +/0.3 cm respectively. The total length of the high-pressure zone was 4.08 +/0.61 cm. The distance between the peak pressure within the gastric sling and clasp muscle fiber complex and the crural diaphragm was 1.7 +/0.53cm and the distance between the crural diaphragm and the LEC was 1.4 +/-0.48. CONCLUSIONUsing high spatial resolution manometry within the high-pressure zone of the gastroesophageal junction, it is possible to resolve the high-pressure zone into 3 distinct and separate components. These components represent the gastric sling and clasp fiber muscle complex in the proximal stomach, the crural diaphragm measured in the distal esophagus and the LEC muscle proximal to the CD. The average pressure, width and distance between these components were measured.

Background: We recently showed that the gastric sling/clasp muscle complex does not contribute to the high pressure zone in GERD patients indicating a role in pathophysiology. Aim: We determined the cholinergic contractile response in clasp, sling and lower esophageal circular (LEC) fibers. Methods: Stomach and esophagi were obtained from 17 human transplant donors: 11 with no GERD history, 4 with probable GERD (proton pump inhibitor use) and 2 with definite GERD (Barrett's esophagitis). The contractile response to increasing carbachol concentrations was determined. Muscarinic receptor density was measured by subtype selective immunoprecipitation of [3]H-QNB binding. Results: Clasp and LEC fibers from definite GERD have decreased maximal contractile response. Contractility is increased in sling fibers of both definite and probable GERD. Concentrations of carbachol higher than 100 μM induce relaxations that are decreased in clasp fibers of probable and definite GERD. Relaxations are greater in sling fibers from definite GERD and higher in LEC from probable and definite GERD. Total and M2 receptor density is statistically lower in the GERD than non-GERD specimens in both clasp and sling fibers and M3 density is statistically lower in GERD than non-GERD clasp fibers. Conclusion: This suggest that a myogenic defect in clasp fibers may be involved in GERD pathophysiology in the organ donors with Barrett's esophagitis. The greater contractile response in the sling fibers from GERD donors suggest a possible compensatory mechanism for the lack of contractility of the clasp muscle fibers.

This study determined how closely the contractile physiology of the pig gastroesophageal junction follows the human. We obtained human tissue from organ transplant donors and pig tissue from a slaughterhouse. Total, M-2 and M-3 receptor density was determined by subtype specific immunoprecipitation. Total and M-2 are higher in pig than human. M-3 receptors are 2 fold higher in human than pig sling and over 2 fold lower in human than pig clasp fibers. The methoctramine and darifenacin potency to inhibit bethanechol contractions, calculated by classic Schild analysis, indicates that both M-2 and M-3 receptors cause contraction which violates the assumption of one receptor causing the effect. An analysis method relating dual occupation of M-2 andM-3 receptors to the contractile response was developed based on the published Ka values of M-2 and M-3 receptors for bethanechol of 170 μM and 110 μM respectively, and mass-action binding which, at equilibrium, gives receptor occupation = [A][R] / ([A] + Ka), where [A] denotes the agonist concentration, [R] is the receptor concentration and Ka is the agonist dissociation constant (reciprocal of affinity). Three dimensional plots for M-2 and M-3 occupation and contractile response are shown in the figure. Although the M-3 receptor subtype density is different between human and pig, the physiology of the contractile response is similar. This indicates that the pig may be a good model for human gastroesophageal junction physiology. Muscarinic receptor density (fMol/mg solubile protein)

The circular muscle fibers at the end of the esophagus are traditionally considered the lower esophageal sphincter. However, the first barrier to gastric reflux is actually the clasp/sling fiber complex of the stomach. Relaxation mediates transient lower esophageal sphincter relaxation underlying the pathophysiology of gastroesophageal reflux disease (GERD). This study determined the pharmacologic specificity of the nicotinic receptor mediated relaxation of pre-contracted strips of human and porcine clasp muscle fibers. Human specimens were obtained from organ transplant donors. Clasp fiber muscle strips were exposed to increasing carbachol concentrations (human) or acetylcholine with physostigmine to block cholinesterase (pig). At concentrations higher than 30 uM, abrupt relaxations were produced. After 60 minutes of repeated washing, strips were exposed to various ganglionic and neuromuscular nicotinic receptor antagonists for 30 minutes then rechallenged with cholinergic agonists. Results, as a percentage of relaxation in time control strips are shown in the figure below. The neuromuscular blockers d-tubocurarine, decamethonium (human) and pancuronium (pig) inhibited relaxation whereas the ganglionic blocker hexamethonium (human) and the alpha7 selective antagonist methyllycaconitine did not. Other ganglionic blockers such as MG624, NDNI and TMPH blocked these relaxations whereas mecamylamine was only partially effective in human tissue. These results indicate that the pharmacology of the nicotinic receptor mediating relaxation of the gastric clasp fibers may be unique and a potential target for development of selective agents for treatment of GERD.