Article Figures & Data
Figures
- Fig. 1.
Schematic overview of the mechanisms governing smooth muscle contraction, including neural stimulation, muscarinic receptor activation, and calcium influx. Acetylcholine (ACh) release from excitatory neurons binds to M receptors on the smooth muscle cell surface. This triggers activation of the Gq/11 protein, which then stimulates phospholipase C (PLC). PLC cleaves phosphatidylinositol 4,5-bisphosphate (PIP2) into inositol triphosphate (IP3) and diacylglycerol (DAG). IP3 causes calcium release from the sarcoplasmic reticulum (SR) into the cytoplasm. This cytoplasmic calcium increase, along with calcium influx through voltage-gated and receptor-operated calcium channels (VDCC and ROC), interacts with calmodulin to activate myosin light chain kinase (MLCK). MLCK phosphorylation of myosin leads to crossbridge cycling and smooth muscle contraction. Additionally, myosin light-chain phosphatase (MLCP) is also involved in this intricate regulatory pathway.
- Fig. 2.
Characteristic contraction profiles of both porcine lower esophageal sphincter sling (A) and clasp (B) muscle strips, each demonstratively influenced by escalating concentrations of U46619 at 30, 100, and 300 nM.
- Fig. 3.
Contractile response of porcine lower esophageal sphincter sling (A) and clasp (B) muscle strips to different concentrations of U46619. The elicited contractions are expressed as a percentage of the contraction caused by a standard 1 µM carbachol stimulation. The displayed results are derived from a minimum of four separate experiments, with vertical bars denoting the standard error of the mean. The asterisk (*) indicates a statistically significant difference compared with 10 nM, the hash symbol (#) to 30 nM, and the paragraph symbol (¶) to 100 nM U46619-induced contractions, all at P < 0.05.
- Fig. 4.
Responses of porcine LES to U46619 and various inhibitors. (A) Effects of thromboxane A2 receptor antagonists on U46619-induced contractions in LES sling muscle strips. When strips are treated with either 1 μM seratrodast or 10 μM GR32191 and then exposed to 100 nM U46619, both seratrodast and GR32191 significantly inhibit contractions. The asterisk indicates contractions that are statistically different from those induced by 100 nM U46619 alone (P < 0.05). (B) Effects of various inhibitors on U46619-induced contractions in LES sling muscle. The LES strips are treated with 1 µM TTX, 1 µM atropine, 1 µM nifedipine, or calcium-free Kreb’s solution before exposure to 100 nM U46619. Only nifedipine and the calcium-free Kreb’s solution significantly inhibit contractions. The asterisk indicates contractions that are statistically different from those triggered by 100 nM U46619 alone (P < 0.05).
- Fig. 5.
Amplification of total RNA is shown after reverse transcription with TXA2 receptor-specific primers. The amplified products were analyzed via electrophoresis on an agarose gel, stained with ethidium bromide, and visualized under UV light. The results displayed, representative of three separate experiments, confirm the presence of TXA2 receptor PCR products in both the sling and clasp muscles (lane TXA2R). As an internal control, the β-actin specific PCR product of 148 bp is presented (lane ACTB).
- Fig. 6.
Immunohistochemical examination of paraffin-embedded sling and clasp muscle fibers, stained with TXA2 receptor-specific antibodies. Notably, immunostaining for the TXA2 receptor is observed within the smooth muscle (SM) of both lower esophageal sphincter sling (A) and clasp (B) muscle fibers (magnified 400x). As a control, sections stained with equimolar concentrations of normal rabbit IgG, serving as a negative control, are also provided for both the sling (C) and clasp (D) muscles (magnified 400x).
