AIM:To investigate the pathway(s)mediating rat antral circular smooth muscle contractile responses to the cholinomimetic agent,bethanechol and the subtypes of muscarinic receptors mediating the cholinergic contraction...AIM:To investigate the pathway(s)mediating rat antral circular smooth muscle contractile responses to the cholinomimetic agent,bethanechol and the subtypes of muscarinic receptors mediating the cholinergic contraction. METHODS:Circular smooth muscle strips from the antrum of Sprague-Dawley rats were mounted in muscle baths in Krebs buffer.Isometric tension was recorded.Cumulative concentration-response curves were obtained for(+)-cis- dioxolane(cD),a nonspecific muscarinic agonist,at 10^(-8)- 10^(-4)mol/L,in the presence of tetrodotoxin(TTX,10^(-7)mol/L). Results were normalized to cross sectional area.A repeat concentration-response curve was obtained after incubation of the muscle for 90 min with antagonists for M1(pirenzepine), M2(methoctramine)and M3(darifenadn)muscarinic receptor subtypes.The sensitivity to PTX was tested by the ip injection of 100 mg/kg of PTX 5 d before the experiment.The antral circular smooth muscles were removed from PTX-treated and non-treated rats as strips and dispersed smooth muscle cells to identify whether PTX-linked pathway mediated the contractility to bethanechol. RESULTS:A dose-dependent contractile response observed with bethanechol,was not affected by TTx.The pretreatment of rats with pertussis toxin decreased the contraction induced by bethanechol.Lack of calcium as well as the presence of the L-type calcium channel blocker,nifedipine,also inhibited the cholinergic contraction,with a reduction in response from 2.5±0.4 g/mm^2 to 1.2±0.4 g/mm^2(P<0.05).The dose- response curves were shifted to the right by muscarinic antagonists in the following order of affinity:darifenacin (M_3)>methocramine(M_2)>pirenzepine(M_1). CONCLUSION:The muscarinic receptors-dependent contraction of rat antral circular smooth muscles was linked to the signal transduction pathway(s)involving pertussis-toxin sensitive GTP-binding proteins and to extracellular calcium via L-type voltage gated calcium channels.The presence of the residual contractile response after the treatment with nifedipine,suggests that an additional pathway could mediate the cholinergic contraction.The involvement of more than one muscarinic receptor(functionally predominant type 3 over type 2)also suggests more than one pathway mediating the cholinergic contraction in rat antrum.展开更多
Objective: Exploring the intra axonal overloading of calcium ion (Ca 2+ ) in brain diffuse axonal injury (DAI) and the therapeutic effect of calcium antagonist(Nimotop) on DAI. Methods: Fourteen SD rats were ...Objective: Exploring the intra axonal overloading of calcium ion (Ca 2+ ) in brain diffuse axonal injury (DAI) and the therapeutic effect of calcium antagonist(Nimotop) on DAI. Methods: Fourteen SD rats were divided into injury group, treatment group and control group. The DAI model of rats was produced by using a head instant axial rotation device. Tissues from the medulla oblongata of rats were taken 2 24 h post injury and processed for electron microscopic observation by a cytochemical technique for calcium ion. Results: In the injured rats there was evidence of local disruption of myelin sheath,lucent spaces between myelin sheath lamellae, separation of axolemma from the inner layer of myelin sheath, peripheral accumulation of organellae, intra axonal formation of vacuoles and reduction of mitochondria. A large number of fine calcium deposits were seen on the affected myelin sheath. The severity of the myelin sheath lesion was related positively to the number of calcium deposits on it. In the later post injury period the coarse calcium particles appeared within the damaged axon. Neuronal somas and microvascular endotheliums showed a lot of vacuoles and some fine calcium deposits. Many microvilli formed on the luminal aspect of endothelium. In the treatment group myelin sheath tended to be injured locally, and axoplasmic mitochondria were nearly normal in number, structure, and distribution. Few calcium deposits were found in axons. Vacuolization was obviously reduced in neuronal soma and endothelium. Conclusions: In DAI there exists an intra axonal overloading of calcium ion, which is a key factor to the occurrence and development of DAI. Early use of Nimotop can alleviate DAI.展开更多
文摘AIM:To investigate the pathway(s)mediating rat antral circular smooth muscle contractile responses to the cholinomimetic agent,bethanechol and the subtypes of muscarinic receptors mediating the cholinergic contraction. METHODS:Circular smooth muscle strips from the antrum of Sprague-Dawley rats were mounted in muscle baths in Krebs buffer.Isometric tension was recorded.Cumulative concentration-response curves were obtained for(+)-cis- dioxolane(cD),a nonspecific muscarinic agonist,at 10^(-8)- 10^(-4)mol/L,in the presence of tetrodotoxin(TTX,10^(-7)mol/L). Results were normalized to cross sectional area.A repeat concentration-response curve was obtained after incubation of the muscle for 90 min with antagonists for M1(pirenzepine), M2(methoctramine)and M3(darifenadn)muscarinic receptor subtypes.The sensitivity to PTX was tested by the ip injection of 100 mg/kg of PTX 5 d before the experiment.The antral circular smooth muscles were removed from PTX-treated and non-treated rats as strips and dispersed smooth muscle cells to identify whether PTX-linked pathway mediated the contractility to bethanechol. RESULTS:A dose-dependent contractile response observed with bethanechol,was not affected by TTx.The pretreatment of rats with pertussis toxin decreased the contraction induced by bethanechol.Lack of calcium as well as the presence of the L-type calcium channel blocker,nifedipine,also inhibited the cholinergic contraction,with a reduction in response from 2.5±0.4 g/mm^2 to 1.2±0.4 g/mm^2(P<0.05).The dose- response curves were shifted to the right by muscarinic antagonists in the following order of affinity:darifenacin (M_3)>methocramine(M_2)>pirenzepine(M_1). CONCLUSION:The muscarinic receptors-dependent contraction of rat antral circular smooth muscles was linked to the signal transduction pathway(s)involving pertussis-toxin sensitive GTP-binding proteins and to extracellular calcium via L-type voltage gated calcium channels.The presence of the residual contractile response after the treatment with nifedipine,suggests that an additional pathway could mediate the cholinergic contraction.The involvement of more than one muscarinic receptor(functionally predominant type 3 over type 2)also suggests more than one pathway mediating the cholinergic contraction in rat antrum.
文摘Objective: Exploring the intra axonal overloading of calcium ion (Ca 2+ ) in brain diffuse axonal injury (DAI) and the therapeutic effect of calcium antagonist(Nimotop) on DAI. Methods: Fourteen SD rats were divided into injury group, treatment group and control group. The DAI model of rats was produced by using a head instant axial rotation device. Tissues from the medulla oblongata of rats were taken 2 24 h post injury and processed for electron microscopic observation by a cytochemical technique for calcium ion. Results: In the injured rats there was evidence of local disruption of myelin sheath,lucent spaces between myelin sheath lamellae, separation of axolemma from the inner layer of myelin sheath, peripheral accumulation of organellae, intra axonal formation of vacuoles and reduction of mitochondria. A large number of fine calcium deposits were seen on the affected myelin sheath. The severity of the myelin sheath lesion was related positively to the number of calcium deposits on it. In the later post injury period the coarse calcium particles appeared within the damaged axon. Neuronal somas and microvascular endotheliums showed a lot of vacuoles and some fine calcium deposits. Many microvilli formed on the luminal aspect of endothelium. In the treatment group myelin sheath tended to be injured locally, and axoplasmic mitochondria were nearly normal in number, structure, and distribution. Few calcium deposits were found in axons. Vacuolization was obviously reduced in neuronal soma and endothelium. Conclusions: In DAI there exists an intra axonal overloading of calcium ion, which is a key factor to the occurrence and development of DAI. Early use of Nimotop can alleviate DAI.
