Involvement of different receptor subtypes in prostaglandin E2-induced contraction and relaxation in the lower esophageal sphincter and esophageal body

PGE2 binding to EP2 promotes ureteral stone expulsion by relaxing ureter via the cAMP-PKA pathway

BACKGROUND

This study investigated the relaxation effect of PGE2 on the ureter and its role in promoting calculi expulsion following calculi development.

METHODS

By using immunofluorescence and Western blot, we were able to locate EP receptors in the ureter. In vitro experiments assessed the impact of PGE2, receptor antagonists, and agonists on ureteral relaxation rate. We constructed a model of ureteral calculi with flowable resin and collected ureteral tissue from postoperative side of the ureter after obstruction surgery. Western blot analysis was used to determine the protein expression levels of EP receptors and the PGE2 terminal synthase mPGES-1. Additionally, PGE2 was added to smooth muscle cells to observe downstream cAMP and PKA changes.

RESULTS

The expression of EP2 and EP4 proteins in ureteral smooth muscle was verified by Western blot analysis. According to immunofluorescence, EP2 was primarily found on the cell membrane, while EP4 was found in the nucleus. In vitro, PGE2 induced concentration-dependent ureteral relaxation. Maximum diastolic rate was 70.94 ± 4.57% at a concentration of 30µM. EP2 antagonists hindered this effect, while EP4 antagonists did not. Obstructed ureters exhibited elevated mPGES-1 and EP2 protein expression (P < 0.01). Smooth muscle cells treated with PGE2 displayed increased cAMP and phosphorylated PKA.

CONCLUSIONS

PGE2 binding to EP2 induces ureteral relaxation through the cAMP-PKA pathway. This will provide a new theoretical basis for the development of new therapeutic approaches for the use of PGE2 in the treatment of ureteral stones.

Measurement of Intracellular Ca2+ for Studying GPCR-Mediated Lipid Signaling

Intracellular Ca2+ can be conveniently monitored by sensitive Ca2+ fluorescent dyes in live cells. The Gαq involved lipid signaling pathways and, thus, can be studied by intracellular Ca2+ imaging. Here we describe the protocols to measure intracellular Ca2+ for studying PEG2-EP1 activity in esophageal smooth muscle cells. The ratiometric Fura-2 imaging provides quantitative data, and the Fluo-4 confocal microscopic imaging has high-spatial resolution.

Effects of standardized [6]-gingerol extracts and [6]-gingerol on isolated ileum and lower esophageal sphincter contractions in mice

Standardized [6]-gingerol extracts were prepared by microwave-assisted extraction using 20% v/v glycerin in ethanol and 20% v/v eutectic mixture of sucrose and citric acid in ethanol as alternative green solvents. The extracts obtained from 20% v/v glycerin in ethanol (GEE) and 20% v/v eutectic mixture of sucrose and citric acid in ethanol (EMSCEE) were standardized by HPLC to contain 17.0 mg/g of [6]-gingerol. The effects of the extracts on mouse ileal contractions via M3 and 5-HT3 receptors as well as lower esophageal sphincter (LES) contraction were determined in vitro relative to the marker compound, [6]-gingerol. [6]-Gingerol, GEE and EMSCEE demonstrated significant and concentration-dependent inhibitory effects on ileal contraction in mice via M3 and 5-HT3 receptors in a noncompetitive manner. In addition, [6]-gingerol and EMSCEE tend to increase the LES tone. These results indicated the potential of GEE and EMSCEE to attenuate nausea and vomiting and might be used as nutraceuticals.