Modulating activity of M1 receptor to the reaction of ileal smooth muscle.

BACKGROUND: The subject of the study was determination of the effect of drugs on ileal smooth muscle contraction induced by activation of M(1) type muscarinic receptors. Drugs that have an effect on muscarinic receptors are divided to agonists, with close ties to the receptor and high internal activity and antagonists, with no internal activity. Conducted experiments tested interactions between a broad-spectrum agonist of muscarinic receptors, carbachol and a selective muscarinic receptor antagonist of M(1) type, pirenzepine. MATERIAL/METHODS: Testing was conducted on tissues isolated from rat's intestine. Male Wistar rats with weight between 220 g and 360 g were anesthetized by intraperitoneal injection of urethane (120 mg/kg). Concentration-effect curves were determined with the use of cumulated concentration method, in accordance with the van Rossum method (1963) in Kenakin modification (2006). RESULTS: The purpose of the study was determination of concentration-effect curves for carbachol. This curve was compared with the curve of receptor occupation depending on concentration of this drug. Based on concentration-effect curves, the average value of EC(50) was calculated for carbachol, amounting to 2.44×10(-6) [M/l]. CONCLUSIONS: The results confirmed that atropine is effective in stopping contractions caused by carbachol, meeting the conditions of competitive antagonists. Atropine caused the shift of curves for carbachol to the right. Pirenzepine, selectively blocking muscarinic receptors of M(1) type gave similar results. It was proved that in the preparation of gastric fundus smooth muscle, M(1) type receptors occur not only presynaptically, but also postsynaptically.

Activity of guanylyl cyclase activators on the reaction of tracheal smooth muscle contraction.

INTRODUCTION: The subject of the study compare the influences of YC-1 guanylyl cyclase activator with ODQ guanylyl cyclase inhibitor on the tracheal smooth muscle contraction induced by carbachol. The study specified the influence of increasing concentrations of soluble guanylyl cyclase activators YC-1 and 8Br cGMP on the reaction of tracheal smooth muscle contraction released by carbachol. The author also examined the effect of increasing concentrations of soluble guanylyl cyclase inhibitor ODQ on the concentration-effect curves for carbachol. MATERIAL/METHODS: Testing was conducted on an isolated trachea of both sexes of Wistar rats with weight ranging between 350 g and 450 g. Tracheas were prepared in accordance with the Akcasu (1959) method in Szadujkis-Szadurski (1996) modification. Concentration-effect curves were determined with the use of cumulated concentration method, in accordance with the van Rossum method (1963) in Kenakin (2006) modification. RESULTS: According to conducted testing, activation of soluble guanylyl cyclase with the use of YC-1 and 8Br cGMP caused reduced reaction of the tracheal smooth muscle with carbachol on average to 80%. Comparing concentration-effect curves for carbachol before and after the use of 8Br cGMP, similar results were obtained for those released by YC-1. On the other hand, increasing concentrations of guanylyl cyclase inhibitor - ODQ cause shift of curves to the left, decrease of EC(50) value and an increase of maximum reaction to carbachol. CONCLUSIONS: Carbachol, depending on concentration, causes tracheal smooth muscle contraction. According to testing, we can confirm that activation of guanylyl cyclase leads to reduction of the reaction of tracheal smooth muscle to carbachol on average up to 80%

Role of calcium and calmodulin in reaction of gastric fundus contraction.

BACKGROUND: The subject of this study is determination of the influence of calmodulin and calcium on gastric fundus smooth muscle contraction. During experiments, the author tested the influence of a serotonin receptor agonist, serotonin (5-HT), causing smooth muscle contraction. MATERIAL/METHODS: Testing was conducted on tissues isolated from rat's stomach. Male Wistar rats with weight between 220 g and 360 g were anesthetized by intraperitoneal injection of urethane (120 mg/kg). The stomach was dissected, and later the gastric fundus was isolated. Tissue was placed in a dish for insulated organs with 20 ml in capacity, filled with Krebs fluid. Results contained in the study are average values ± SE. In order to determine statistical significance, the principles of receptor theory were used (Kenakin modification). RESULTS: According to conducted tests, we can deduce that 8 Br cGMP stops the reaction of gastric fundus smooth muscle contraction induced by serotonin. The use of 8Br-cGMP in the range of concentrations between 10 and 300 µM leads to reduction of maximum effect from 100% to 46%. Similar changes were obtained after the use of guanylate cyclase activator (CG) - YC-1. Curves for the contractile activity of serotonin along with an increase of concentration YC-1 are shifted to the right, and the maximum effect of reaction decreases. Increasing concentrations of flunarizine, a calmodulin antagonist, in a concentration-dependent way blocks binding between calcium and calmodulin, and at the same time leads to the shift of concentration-effect curves for serotonin to the right and a decrease of maximum reaction. Increasing concentrations of ODQ, a guanylate cyclase inhibitor lead to statistically significant shift of the curves to the left, decrease of EC(50) value and simultaneous increase of maximum reaction to serotonin. CONCLUSIONS: According to conducted testing, serotonin causes gastric fundus smooth muscle contraction dependent on concentration. Reaction of contraction induced by serotonin is stopped by a calmodulin antagonist, flunarizine. In addition, experiments confirmed participation of cyclical nucleotides in blocking reaction of gastric fundus contraction.

Role of M1 receptor in regulation of gastric fundus smooth muscle contraction.

BACKGROUND: The subject of this study is determination of the influence of drugs on gastric fundus smooth muscle contraction induced by activation of muscarinic receptors M1. Experiments tested interactions between a receptor agonist, carbachol and muscarinic receptor antagonists, atropine and pirenzepine. MATERIAL/METHODS: Testing was conducted on tissues isolated from rat's stomach. Male Wistar rats with weight between 220 g and 360 g were anesthetized by intraperitoneal injection of urethane (120 mg/kg). The stomach was dissected, and later the gastric fundus was isolated. Tissue was placed in a dish for insulated organs with 20 ml in capacity, filled with Krebs fluid. Results contained in the study are average values ± SE. In order to determine statistical significance, the principles of receptor theory were used (Kenakin modification). RESULTS: According to tests, carbachol, in concentrations ranging between 10(-8) M to 10(-4) M, in a dosage-dependent way induces gastric fundus smooth muscle contraction. Presented results indicate that carbachol meets the conditions posed to full agonists. On the other hand, atropine, a non-selective muscarinic receptor antagonist, causes a concentration-dependent shift of concentration-effect curve (for carbachol) to the right, maintaining maximum reaction. According to analysis of the curve determined, we can deduce that atropine meets the conditions posed to competitive antagonists. The use of pirenzepine, a competitive receptor agonist M1, causes shift of concentration-effect curve (for carbachol) to the right, maintaining maximum reaction. CONCLUSIONS: From the testing conducted on the preparation of the gastric fundus we can deduce that atropine causes shift of concentration-effect curves for carbachol to the right. A similar effect is released by pirenzepine, selectively blocking muscarinic receptors of M1 type. The results indicate that in the preparation of the gastric fundus smooth muscle, M1 type receptors occur also postsynaptically.

The role of calcium in modulating the reactivity of the smooth muscle cells during ischemia/reperfusion. Part 1.

BACKGROUND: Calcium ions regulate the function of cells in many ways, acting as first messengers of intercellular information and second messengers of intracellular information. Changes in cytoplasmic calcium levels depend on calcium influx from the extracellular space or calcium release from cellular stores. Increase in calcium ion concentration takes place in pathological situations, such as ischemia. In the present study the roles of calcium and G protein in contraction induced by angiotensin II (agonist of the metabotropic receptor AT1), phenylephrine (agonist of alpha1-adrenergic metabotropic receptor), and Bay K8644 (a calcium channel agonist) after ischemia/reperfusion were investigated. MATERIAL/METHODS: Experiments were performed on perfused male Wistar rats' tail arteries. Contraction induced by angiotensin II, phenylephrine, and Bay K8644 mediated by intracellular or extracellular calcium after ischemia/reperfusion and in the presence of the blocker of G protein Bordetella pertussis toxin (P 7208) was analyzed. RESULTS: Ischemia reduced while reperfusion augmented the response of vascular smooth muscle cells to angiotensin II and phenylephrine, but they did not change the effects of Bay K8644. P 7208 decreased the effects of phenylephrine mediated by intracellular and extracellular calcium and reduced the reactions of angiotensin II mediated only by intracellular calcium, but did not change the effects of Bay K8644. CONCLUSIONS: Ischemia/reperfusion modulates vascular contraction induced by angiotensin II and phenylephrine. Both intracellular and extracellular calcium ions mediate the contraction induced by angiotensin II and phenylephrine. The results suggests that G protein modulates the effects of angiotensin II mediated by intracellular calcium ions while it plays a role in the reactions of phenylephrine mediated by calcium coming from both sources, intracellular and extracellular.

The role of calcium in modulating the reactivity of the smooth muscle cells during ischemia/reperfusion. Part 2.

BACKGROUND: Damage of transplanted organs during reperfusion is still a problem that prompts the search for new drugs able to diminish the risk of graft rejection. The aim of this study was to examine the influence of antioxidant system on the contraction of arteries induced by angiotensin II during ischemia/reperfusion and to determine the role of intracellular and extracellular calcium ions under these conditions. MATERIAL/METHODS: The experiments were performed on male Wistar rats' tail arteries. The effects of angiotensin II on vascular tone were examined after ischemia/reperfusion in the presence of catalase or aminotriazole. To determine the role of intracellular and extracellular Ca(2+), the experiments were performed in Ca(2+)-free PSS and PSS. RESULTS: Angiotensin II increased perfusion pressure in both Ca(2+)-free PSS and PSS. After ischemia, the reactions induced by angiotensin II were lower, while after reperfusion they were higher. In the presence of catalase the effects induced by angiotensin II were lower and in the presence of aminotriazole higher. CONCLUSIONS: Ischemia inhibits and reperfusion augments the perfusion pressure induced by angiotensin II. The results confirm the vasoprotective effect of catalase and the destructive influence of aminotriazole in modulating the reactions of vascular smooth muscle cells to ANG II after ischemia/reperfusion. These results suggest that the antioxidant system plays a role in modulating the reactions induced by angiotensin II after ischemia/reperfusion and that reperfusion disturbs the balance between antioxidants and the production of reactive oxygen species.