A range of concentrations (1nM to 30μM) of acetylcholine (Ach) and
5-hydroxytryptamine (5-HT) was administered to organ bath containing rat ileum. Ach and 5-HT induced contractions from 3nM (Fig. 1) and 10nM (Fig. 2) onwards respectively, both generating a shallow slope at the beginning of the concentration-response curve. EC50 of Ach is 7.47 x 10-7M whereas EC50 of 5-HT is 7.97 x 10-7M. The contraction generated by Ach and 5-HT was expressed in % Emax. As shown in Fig. 1 and 2, % Emax increased with increasing agonists concentrations and 100% Emax was achieved at a concentration of 30μM. Presence of error bars in both figures indicated the presence of variability in data. We then investigated the effect of Ach and 5-HT …show more content…
Muscarinic acetylcholine receptors (MAchR) and serotonin (5-HT) receptors which belong to the family of G protein-coupled receptor (GPCR) are well-known for their role in regulating contractions of smooth muscle in the gastrointestinal tract with primarily M3 receptors and 5-HT2A receptors contributing to muscle contractions respectively. The present results clearly demonstrate that rat ileum contracts in response to agonists Ach (Fig. 1) and 5-HT (Fig. 2). Ach binds to M3 receptor coupled to Gq protein, stimulating enzyme phospholipase C (PLC) which cleaves phosphatidylinositol (4,5)-bisphosphate (PIP2) into inositol trisphosphate (IP3) and diacylglycerol (DAG). A rise in IP3 level aids release of Ca2+ from sacroplasmic reticulum whereas DAG activates protein kinase C (PKC), leading to phosphorylation of various proteins. Increased cytosolic Ca2+ level promotes binding of Ca2+ to calmodulin, increasing the Ca2+/calmodulin concentration which is essential in activating myosin light chain kinase (MLCK). MLCK then phosphorylates myosin light chain (MLC), leading to the formation of cross-bridge between actin and myosin, thus …show more content…
Table 2 showed that metergoline suppressed the activity of 5-HT by 7.24mN. The rationale behind is that metergoline exhibits pharmacological antagonism by irreversibly inhibiting 5-HT2A receptor and reducing the amount of agonist-receptor complexes formed. The effect of antagonism by metergoline is insurmountable and often lasts until new 5-HT2A receptors can be synthesized by the cell. However, change in Ach-induced contractile activity of rat ileum observed with metergoline was too small and is rather insignificant to imply any biological mechanism taking place (Table 1). This implies that metergoline has no inhibitory effect on
5-hydroxytryptamine (5-HT) was administered to organ bath containing rat ileum. Ach and 5-HT induced contractions from 3nM (Fig. 1) and 10nM (Fig. 2) onwards respectively, both generating a shallow slope at the beginning of the concentration-response curve. EC50 of Ach is 7.47 x 10-7M whereas EC50 of 5-HT is 7.97 x 10-7M. The contraction generated by Ach and 5-HT was expressed in % Emax. As shown in Fig. 1 and 2, % Emax increased with increasing agonists concentrations and 100% Emax was achieved at a concentration of 30μM. Presence of error bars in both figures indicated the presence of variability in data. We then investigated the effect of Ach and 5-HT …show more content…
Muscarinic acetylcholine receptors (MAchR) and serotonin (5-HT) receptors which belong to the family of G protein-coupled receptor (GPCR) are well-known for their role in regulating contractions of smooth muscle in the gastrointestinal tract with primarily M3 receptors and 5-HT2A receptors contributing to muscle contractions respectively. The present results clearly demonstrate that rat ileum contracts in response to agonists Ach (Fig. 1) and 5-HT (Fig. 2). Ach binds to M3 receptor coupled to Gq protein, stimulating enzyme phospholipase C (PLC) which cleaves phosphatidylinositol (4,5)-bisphosphate (PIP2) into inositol trisphosphate (IP3) and diacylglycerol (DAG). A rise in IP3 level aids release of Ca2+ from sacroplasmic reticulum whereas DAG activates protein kinase C (PKC), leading to phosphorylation of various proteins. Increased cytosolic Ca2+ level promotes binding of Ca2+ to calmodulin, increasing the Ca2+/calmodulin concentration which is essential in activating myosin light chain kinase (MLCK). MLCK then phosphorylates myosin light chain (MLC), leading to the formation of cross-bridge between actin and myosin, thus …show more content…
Table 2 showed that metergoline suppressed the activity of 5-HT by 7.24mN. The rationale behind is that metergoline exhibits pharmacological antagonism by irreversibly inhibiting 5-HT2A receptor and reducing the amount of agonist-receptor complexes formed. The effect of antagonism by metergoline is insurmountable and often lasts until new 5-HT2A receptors can be synthesized by the cell. However, change in Ach-induced contractile activity of rat ileum observed with metergoline was too small and is rather insignificant to imply any biological mechanism taking place (Table 1). This implies that metergoline has no inhibitory effect on