A Minority of Muscarinic Receptors Mediate Rabbit Tracheal Smooth Muscle Contraction
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To enhance our understanding of cholinergic mechanisms and muscarinic receptors in bronchoconstriction, we have characterized the muscarinic receptor subtypes in rabbit tracheal smooth muscle using radioligand binding and functional assays. The Kd for [3H]quinuclidinyl benzilate ([3H](−)QNB) binding determined from saturation isotherms was 12.6 ×/÷ 1.1 pM (geometric mean ×/÷ SEM), and the Bmax was 269 ± 7 fmol/mg protein (arithmetic mean ± SEM). Competitive inhibition studies with the muscarinic antagonists pirenzepine (PZ), 11[[2-[(diethylamino)-methyl]1-piperidinyl]acetyl]-5,11-dihydro-6H-pyrido-[2,3-b][1,4]benzodiazepine-6-one (AF-DX116), 4-diphenylacetoxy-N-methylpiperidine methobromide (4-DAMP), and hexahydrosiladifenidol (HHSiD) demonstrated heterogeneity of muscarinic receptor sub-types in rabbit tracheal smooth muscle. PZ bound with low affinity to a single receptor site, indicative of an absence of M1 receptors. AF-DX116 (M2 selective) bound with high affinity to approximately 83% of muscarinic binding sites, and 4-DAMP and HHSiD (M3 antagonists) bound with high affinity to approximately 24 and 28% of muscarinic binding sites, respectively. Additionally, direct binding studies with [3H]4-DAMP demonstrated high-affinity binding with 23% of muscarinic binding sites. Thus, the majority of muscarinic receptors in rabbit tracheal smooth muscle bound with high affinity to an M2-selective antagonist, and the remaining receptor sites bound with high affinity to M3 antagonists. The inhibitory effects of atropine, PZ, AF-DX116, and 4-DAMP on methacholine-induced contraction of rabbit tracheal rings were compared. 4-DAMP was a potent inhibitor of methacholine-induced contraction, but PZ and AF-DX116 demonstrated low potency. Our data suggest that methacholine-induced contraction in rabbit tracheal smooth muscle is mediated by the relative minority of receptors (17 to 28%) that bind with high affinity to the M3 muscarinic antagonists, 4-DAMP and HHSiD.Keywords:
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On isolated isthmus of oviduct of the rabbit, Isocorydine (Isoc) (3 mu mol/L) decreased significantly the frequency of spontaneous contraction and muscle tension, but not the amplitude of contraction. The tension and frequency of spontaneous contraction can be suppressed by Isoc at concentrations from 3 to 300 mumol/L. The amplitude of contraction was decreased only at 300 mu mol/L. It is suggested that the frequency and tension of spontaneous contraction of isthmic muscle are more sensitive to Isoc than the amplitude. Isoc antagonized the norepinephrine-induced contraction of the oviduct. The transport of ova through the oviduct reduced by hCG could be delayed by Isoc.
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To investigate the role of ligustrazine on relaxation of the isolated rabbit corpus cavernosum tissue in vitro, the effects of ligustrazine on the corpus cavernosum were observed by using experimental method of smooth muscle strips. Concentration-responses to phenylephine (PE) and KCl were recorded. The results showed that ligustrazine concentration-dependently depressed the contraction response of smooth muscle strips induced by PE. The maximum percentage relaxation of cavernosal strips by ligustrazine was 74.1% ±6.2 % (compared with control: 21.9 % ±5.6 %, P ＜0.01). Ligustrazine concentration-dependently reduced the amplitude of the contraction induced by cumulative doses of PE or KCl, shifted the cumulative concentration response curves of PE and KCl to the right and depressed their maximal responses. It was concluded that ligustrazine could significantly relax the cavernosal muscle contraction induced by PE in vitro. The results suggested that ligustrazine inhibited calcium ion influx.
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Vas deferens
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Objective:Based on the knowledge of special structure of muscle and a mechanochemical actin-activated myosin ATPase cycle four-state model,the relationship between the muscle contraction force and the contraction velocity is discussed.According to up-building a mechanical model,the relationship between the muscle contraction force and the contraction velocity is discussed thoroughly.Methods:With experimental results of single molecule myosin the relationship between the muscle contraction force and the contraction velocity is proposed from the view of physics by the chemical kinetic method and biochemical thermodynamic theory,and the relationship between the muscle contraction force and the contraction velocity is calculated.Results:We find the relationship is similar with the Formula Hill.The theoretical results are consistent with that of experiment.The chemical reaction of muscle contraction is accommodated automatically according to the change of load in muscle,the force of friction is relative to the load in muscle contraction.Conclusions:The model is fit to discussing the relation between the muscle contraction force and the contraction velocity and the method of physics is also fit to studying the system in this article.
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In quiescent cultures of rabbit aortic smooth muscle cells, 12-O-tetradecanoylphorbol-13-acetate (TPA) induced DNA synthesis to some extent in the presence of rabbit plasma-derived serum but inhibited the rabbit whole blood serum (WBS)-induced DNA synthesis and increase in cytoplasmic free Ca2+ concentration Ca2+]i). Prolonged treatment of the cells with phorbol-12,13-dibutyrate (PDBu) caused the partial down-regulation of protein kinase C to a level of 25-35% of that in control cells. In these PDBu-pretreated cells, TPA neither induced DNA synthesis nor inhibited the WBS-induced DNA synthesis, but still inhibited the WBS-induced increase in [Ca2+]i. These results suggest that there are down-regulation-sensitive and -resistant types of protein kinase C in rabbit aortic smooth muscle cells; that the down-regulation-sensitive type has the proliferative and antiproliferative actions whereas the down-regulation-resistant type lacks them; and that the down-regulation-resistant type has the activity to inhibit the WBS-induced increase in [Ca2+]i.
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cGMP-dependent protein kinase
Lagomorpha
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Background/Purpose. In our previous studies, we showed that ER-JIN Decalculous Decoction (EJDD) could prevent and dissolve experimental bladder calculi. The purpose of this study was further to explore whether EJDD affects the ureteral smooth muscle. Methods. Isolated porcine ureteral smooth muscle was used to investigate the mechamism of EJDD. The smooth muscle was vertically hung in an organ bath comprising 10 mL Kreb's Ringer solution at 37 C with 95% O2 and 5% CO2. Results. Norepinephrine (NE), 5-hydroxytryptamine (5-HT) and PGF(subscript 2a) augmented the frequency and potency of spontaneous smooth muscle contraction in a dose-dependent manner. NE at 1×10^(-4) M and 5-HT at 1×10^(-5) M induced tonic contraction. Spontaneous contraction was inhibited by isoproterenol. EJDD (0.25 to 2 mg/mL) enhanced the frequency and potency of spontaneous contraction in a concentraction-independent manner. EJDD also inhibited the tonic contractions induced by high concentrations of NE and 5-HT. However, the spontaneous contractions induced by NE, 5-HT and PGF(subscript 2a)were inhibited by pretreatment with EJDD. Conclusion. The results suggest that EJDD targets the α, β and 5-HT receptors in islolated procine ureters. The complex effects of EJDD were dependent on endogenous spontaneous contractivity.
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Objective To investigate the role and mechanism of ligustrazine on relaxing the isolated rabbit corpus cavernosum tissue. Methods The relaxant effects of ligustrazine on corpus cavernosum were observed by using experimental method of smooth muscle strips. Concentration-responses to PE and KC1 were recorded. Results Ligustrazine concentration-dependently depressed the contraction response to PE. The maximum percentage relaxation of cavernosal strips by ligustrazine was (74.1±6.2)% [ compared with control: (21.9±5.6)%, P0.01 ]. Ligustrazine concentration-dependently inhibits the amplitude of the contraction induced by cumulative doses of PE and KC1. Conclusion Ligustrazine significantly relaxes the cavernosal muscle contraction induced by PE in vitro. The results suggested that ligustrazine inhibit calcium ion influx.
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