A technique for studying in vivo the production rate and turnover rate constant of mouse brain M-receptors was established. A single injection of 25 mg / kg of Benzilylcholine Mustard to living mice resulted in 90 % i...A technique for studying in vivo the production rate and turnover rate constant of mouse brain M-receptors was established. A single injection of 25 mg / kg of Benzilylcholine Mustard to living mice resulted in 90 % irreversible block of brain M-receptors. The time course of the receptor density was then monitored by 3H-QNB binding assay and the production rate and turnover rate constant were calculated from the time course curve with a computer program. It was found that in normal mice the turnover rate constant was about 0.035 h-1 (half-life was about 20 h) and the production rate was 30-42 fmol / (h ·mg protein). Parallel experiments revealed a significant slow down of the turnover of brain M-receptors in hypothyroid mice (turnover rate constant was 0.0257±0.0012 h-1 in hypothyroid vs. 0.0356±0.0021 h-1 in normal) while the production rate was not changed significantly. The results suggest that thyroid hormones have a regulatory action on the turnover of brain M-receptors and the elevation of brain M-receptor density together with slow down of the turnover of brain M- receptors is probably one of the important mechanisms relevant to the brain dysfunction in hypothyroidism.展开更多
AIM: To investigate the pathway (s) mediating rat antral circular smooth muscle contractile responses to the cholinomimetic agent, bebhanechol and the subtypes of muscarinic receptors mediating the cholinergic contrac...AIM: To investigate the pathway (s) mediating rat antral circular smooth muscle contractile responses to the cholinomimetic agent, bebhanechol 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 (+)-cisdioxolane (cD), a nonspecific muscarinic agonist, at 10^-8-10^-4mol/L, in the presence of tetrodotoxin (TTX, 10^-7mol/L). Results were normalized to cross sectional area. A repeat concentration-response curve was obtained after incubation of the muscle for 90min wibh antagonists for M1(pirenzepine), M2(methoctramine) and M3(darifenacin) muscarinic receptor subtypes. The sensitivity to PTX was tested by the ip injection of 100mg/kg of PTX 5d 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 responsefrom 2.5±0.4g/mm^2 to 1.2±0.4g/mm^2(P<0.05), The doseresponse curves were shifted to the right by muscarinic antagonists in the following order of affinity: darifenacin (M3)>methocramine (M2)>pirenzepine (M1). CONCLUSION: The muscarinic receptors-dependent contraction of rat antral circular smooth muscles was linked to the signal transduction pabhway(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
文摘A technique for studying in vivo the production rate and turnover rate constant of mouse brain M-receptors was established. A single injection of 25 mg / kg of Benzilylcholine Mustard to living mice resulted in 90 % irreversible block of brain M-receptors. The time course of the receptor density was then monitored by 3H-QNB binding assay and the production rate and turnover rate constant were calculated from the time course curve with a computer program. It was found that in normal mice the turnover rate constant was about 0.035 h-1 (half-life was about 20 h) and the production rate was 30-42 fmol / (h ·mg protein). Parallel experiments revealed a significant slow down of the turnover of brain M-receptors in hypothyroid mice (turnover rate constant was 0.0257±0.0012 h-1 in hypothyroid vs. 0.0356±0.0021 h-1 in normal) while the production rate was not changed significantly. The results suggest that thyroid hormones have a regulatory action on the turnover of brain M-receptors and the elevation of brain M-receptor density together with slow down of the turnover of brain M- receptors is probably one of the important mechanisms relevant to the brain dysfunction in hypothyroidism.
文摘AIM: To investigate the pathway (s) mediating rat antral circular smooth muscle contractile responses to the cholinomimetic agent, bebhanechol 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 (+)-cisdioxolane (cD), a nonspecific muscarinic agonist, at 10^-8-10^-4mol/L, in the presence of tetrodotoxin (TTX, 10^-7mol/L). Results were normalized to cross sectional area. A repeat concentration-response curve was obtained after incubation of the muscle for 90min wibh antagonists for M1(pirenzepine), M2(methoctramine) and M3(darifenacin) muscarinic receptor subtypes. The sensitivity to PTX was tested by the ip injection of 100mg/kg of PTX 5d 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 responsefrom 2.5±0.4g/mm^2 to 1.2±0.4g/mm^2(P<0.05), The doseresponse curves were shifted to the right by muscarinic antagonists in the following order of affinity: darifenacin (M3)>methocramine (M2)>pirenzepine (M1). CONCLUSION: The muscarinic receptors-dependent contraction of rat antral circular smooth muscles was linked to the signal transduction pabhway(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.
