芒柄花素对兔离体肠平滑肌舒张作用的影响

目的观察芒柄花素对兔离体肠平滑肌肌张力的影响并探讨其作用机制。方法采用经典的离体小肠灌流技术,观察芒柄花素对肠平滑肌收缩活动以及乙酰胆碱(Ach)、氯化钡(BaCl2)及组胺(HA)所致痉挛性收缩肠平滑肌的影响。应用L型钙通道开放剂Bay K8644、肌浆网ryanodine受体阻断剂钌红(RR)和一氧化氮(NO)合酶抑制剂左旋硝基精氨酸甲酯(L-NAME),研究芒柄花素舒张肠平滑肌的作用机制。结果芒柄花素(10、20、40、60、80、100μmol/L)能剂量依赖性的抑制家兔离体小肠平滑肌自发性收缩,对Ach,HA和BaCl2所致的兔离体肠痉挛性收缩也具有剂量依赖性抑制作用,且与无刺激肠平滑肌比较有显著性差异(P<0.05或P<0.01)。芒柄花素可明显抑制Bay K8644(0.5μmol/L),阻断RR引起肠平滑肌舒张作用,但L-NAME不能够抑制芒柄花素舒张肠平滑肌作用。结论芒柄花素显著抑制家兔小肠平滑肌的收缩活动,其抑制可能与抑制细胞外钙内流和内钙释放,从而使细胞内钙浓度降低有关,但与小肠平滑肌一氧化氮(NO)浓度无关。     

Electrode problems in the recording of action potentials in the human small intestine

Spike potentials in the human duodenum were recorded simultaneously with several pairs of bipolar electrodes differing in size, shape, interelectrode distance and orientation. An increase in amplitude was observed with increasing interelectrode distance (1–5 mm), but otherwise the potentials did not differ significantly. Spike potentials recorded with platinum electrodes did not differ from those recorded with copper electrodes of identical size and shape.     

Acetylcholine-induced contraction in human isolated bronchial smooth muscle: role of an intracellular calcium store

The aim of this study was to investigate the role played by an intracellular calcium store in human bronchoconstriction. Human isolated bronchial smooth muscle strips (5-6 mm long, 0.4-0.5 mm wide) were taken from lung specimens during pneumonectomy. Isometric contraction was recorded after stimulation by 10(-4) M acetylcholine in physiological solutions. The amplitude of acetylcholine-induced contractions was measured in the presence and absence of calcium ions in the perfusing medium. When the perfusing medium was switched to a calcium-free solution the amplitude of the acetylcholine-induced contraction was measured with respect to the duration of calcium-free perfusion. The amplitude of the contraction was 82.1 +/- 11.3%, 77.2 +/- 15.4%, 63 +/- 10.6% of the maximum contraction after the strips were perfused in calcium-free solutions for 1, 3 and 5 min respectively. Several successive contractions could be elicited, and even after 20 min of calcium-free perfusion, acetylcholine was still able to elicit contractions. These results suggest that an intracellular calcium store may be involved in human bronchoconstriction. This finding may help further our understanding of the effects of calcium antagonists on human airways.     

Inhibition of airway smooth muscle contraction by airway epithelium in human bronchus]

To clarify the mechanism underlying the inhibitory effect of epithelial cells on smooth muscle contraction, we studied two types of human bronchial tissue preparations: (1) "acceptor" bronchial strip without epithelium, (2) "donor" bronchial ring with or without epithelium. We measured the contractile responses of acceptor bronchial strip surrounded by donor bronchial ring to increasing concentrations of acetylcholine (ACh). Removal of the epithelium of the donor bronchial rings significantly enhanced the contractions of the acceptor bronchial strips. Thus, airway epithelium decreases the airway smooth muscle contraction to ACh in human bronchus. The mechanism of this inhibitory effect of airway epithelium was not due to a change in mechanical property of the airway, nor to a change in diffusion path for the chemical mediators. These results suggest that human airway epithelium may have an important role in modulating airway smooth muscle tone, possibly by the release of an epithelium-derived relaxing factor.     

Molecular model of muscle contraction

A quantitative stochastic model of the mechanochemical cycle of myosin, the protein that drives muscle contraction, is proposed. It is based on three premises: (i) the myosin head incorporates a lever arm, whose equilibrium position adjusts as each of the products of ATP hydrolysis dissociates from the nucleotide pocket; (ii) the chemical reaction rates are modified according to the work done in moving the arm; and (iii) the compliance of myosin's elastic element is designed to permit many molecules to work together efficiently. The model has a minimal number of parameters and provides an explanation, at the molecular level, of many of the mechanical and thermodynamic properties of steadily shortening muscle. In particular, the inflexion in the force-velocity curve at a force approaching the isometric load is reproduced. Moreover, the model indicates that when large numbers of myosin molecules act collectively, their chemical cycles can be synchronized, and that this leads to stepwise motion of the thin filament. The oscillatory transient response of muscle to abrupt changes of load is interpreted in this light.     

The rate-limiting step in muscle contraction

Summary The motion of skinned muscle fibers in chemically controlled bathing solutions is examined to obtain information about the cross bridge cycle. The effects of an ATP regenerating system and ionic strength on both the transient and the steady response to step changes in load are compared. The transient is changed in characteristic ways by these factors, but the steady motion is unaffected. If changes in the transient reflect changes in the rates of making and breaking cross bridges, these results suggest that the rate of physiological contraction is limited by a slow transition in the unattached myosin molecule rather than the making and breaking of cross bridgesper se.

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Der geschwindigkeitsbegrenzende Schritt bei der Muskelkontraktion

Zusammenfassung In Badelösungen bekannter Zusammensetzung wurde die Verkürzung gehäuteter Muskelfasern untersucht, mit dem Ziel, Informationen über den Querbrückenzyklus zu erhalten. Die Effekte eines ATP-regenerierenden Systems und der Ionenstärke auf die transitorische Phase nach stufenweiser Änderung der Last und auf die Verkürzungsgeschwindigkeit nach Erreichen eines Gleichgewichtszustandes werden verglichen. Die Übergangsphase wird durch diese Faktoren in charakteristischer Weise verändert, während der anschließende Verkürzungsprozeß unbeeinflußt bleibt. Sofern Änderungen in der transitorischen Phase Veränderungen in der Geschwindigkeit der Bildung und Ablösung der Querbrücken widerspiegeln, lassen diese Ergebnisse vermuten, daß die Geschwindigkeit der physiologischen Kontraktion durch eine langsame Veränderung am Myosinmolekül im nicht angehefteten Zustand begrenzt wird und nicht durch die Bildung und das Ablösen der Querbrücken per se.

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Paper, presented at the Erwin Riesch Symposium, Tübingen, April 3–7, 1979

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With 3 figures     

Some properties of calcium-induced contraction in the isolated human and guinea-pig tracheal smooth muscle

We studied the effects of the cyclooxygenase inhibitors, indomethacin and aspirin, the leukotriene antagonist, FPL 55712 and the Ca antagonist, verapamil on basal tone and Ca-induced contractions in the human and guinea-pig tracheal muscle. Indomethacin and aspirin usually increased spontaneous tone or Ca-induced contractions in human strips, while consistently decreased tension development in the guinea-pig muscle. FPL 55712 strongly reduced contractions in the human, whereas it had a very weak effect on the guinea-pig muscle. Verapamil had a small inhibitory effect in the human trachea, either at 5.9 or 40 mM K, but markedly suppressed Ca-induced contractions of guinea-pig trachea in 40 mM K and had little effect on contractions in 5.9 mM K in this tissue. It is concluded that active tone in the two different tracheal muscles were controlled by different processes; that different arachidonate by-products may exert an effect on basal tone in the two different muscles; and that different plasma membrane Ca channels may be operative under basal conditions in the different muscles.     

The interaction of acetylcholine and histamine on human bronchial smooth muscle contraction.

The interaction of histamine (Hist) and acetylcholine (ACh) on human isolated bronchial smooth muscle (HIBSM) contraction, and the influence of the epithelium, was assessed using HIBSM obtained from 15 patients undergoing thoracotomy. Cumulative concentration effect curves for ACh and Hist, together with combinations of equipotent concentrations of both agonists, were generated using both epithelium-intact and epithelium-denuded HIBSM. In epithelium-denuded HIBSM both ACh (p less than 0.05) and Hist (p less than 0.005) produced a significantly enhanced maximal response and a 2.1 fold increase in the potency of ACh (p less than 0.02, n = 13). When ACh and Hist were added simultaneously, in equipotent concentrations, to epithelium-intact HIBSM, a significantly less (p less than 0.0005, n = 13) than additive response occurred with only 60% of the predicted maximum response being observed. However, following epithelium removal, an additive interaction between the two agonists (n = 8) occurred. Using HIBSM from five of the original 15 patients, similar experiments were performed to determine the influence of the muscarinic receptor antagonist atropine (0.1 microM) and the H1 receptor antagonist mepyramine (10 microM). Both resulted in a significantly less than additive interaction (40-50% of predicted tensions). Similar experiments were also performed in the presence of the cyclo-oxygenase inhibitor indomethacin (5 microM) and these failed to reverse the inhibition observed in HIBSM contraction (n = 5). The inhibitory interaction between ACh and Hist appears to be epithelium dependent and is not mediated via the release of prostanoids. Thus, there appears to be a complex interaction between contractile agonists and the epithelium, which is not just a simple summation of the activation of individual receptors on HIBSM.     

Serotoninergic neurons in human fetal intestine: an immunohistochemical study

The distribution of 5-hydroxytryptamine-like immunoreactivity was studied in whole-mount preparations of intestine from human fetuses. Immunoreactive nerve cell bodies were located in the myenteric plexus and were occasionally found in the submucous plexus; they were often seen to have long processes. Varicose fibers were found in the ganglia and internodal strands of the myenteric and submucous plexuses, in the deep muscular plexus of the circular muscle, and in the walls of some small mesenteric blood vessels immediately outside the intestine. This study provides evidence for the presence of serotoninergic nerves in the human intestine.     

Evidence for cross-bridge order in contraction of glycerinated skeletal muscle.

The linear dichroism of iodoacetylrhodamine labels attached to the single reactive thiol groups of myosin heads was measured to determine the spatial orientation of myosin cross-bridges in single glycerinated skeletal muscle fibers. We have shown previously that in rigor the chromophoric labels are well ordered and assume an orientation nearly perpendicular to the fiber axis; in the presence of MgADP, a large fraction of probe remains well ordered but the probe attitude assumes a more slanted orientation; in relaxed muscle, the probe order is largely lost, implying a high degree of cross-bridge disorder. In this paper, we report that during isometric contraction a large fraction of the probe shows a high degree of order, suggesting the attachment of approximately equal to 65% of the cross-bridges to actin. These ordered cross-bridges have a probe attitude similar to that of the MgADP-induced static state and hence are in a mechanical state quite distinct from rigor.     

Are intraluminal electrodes reliable for recording myoelectric activity of the small intestine?

In humans except for the postoperative state, electromyographic activity of the small bowel can only be recorded with intraluminal electrodes. The aim of this study was to validate the use of intraluminal electrodes in pigs by comparing the signal recorded from such electrodes to those recorded with surgically implanted electrodes. A polyethylene probe equipped with bipolar ring-shaped electrodes was placed in the lumen of the proximal jejunum of 6 pigs, at the same level as intramuscular implanted electrodes. The signals were recorded in conscious pigs fed normally. By comparison to the myoelectric activity recorded from the intramuscular implanted electrodes, the intraluminal electrodes provided reliable spike burst detection (sensitivity 85 p. 100; positive predictive value 91 p. 100) in the fasted and fed state, and good identification of migrating myoelectric complexes. Spectral analysis showed the same frequency patterns for signals obtained with both types of electrodes. In conclusion, intraluminal ring-shaped electrodes allow reliable detection of small bowel myoelectric activity and may represent a useful tool for motility studies in man.     

Extracellular calcium and human isolated airway muscle: ionophore A23187 induced contraction

In order to investigate the role played by extracellular calcium mobilization in activating human airway contraction, we studied the effects of A23187, a calcium ionophore, in human isolated bronchial spiral strips. In this preparation, ionophore induced a concentration dependent contraction from 10⁻⁷ M to 10⁻⁵ M which resulted from a direct effect on smooth muscle cells and was not a consequence of mediator release. Ionophore-induced contraction was dependent upon an entry of extracellular calcium which did not occur through the verapamil sensitive voltage dependent channel. Maximal ionophore contraction was 97 ± 11% (n = 5) of the maximal histamine contraction but only 46 ± 11% (n = 5) of the maximal carbachol contraction. However, when extracellular calcium concentration was doubled to 5 mM before addition of ionophore, the significant difference in amplitue between carbachol and ionophore maximal contraction was abolished. At physiological calcium concentrations addition of carbachol or histamine to the plateau of the ionophore maximal contraction produced a significant increase in the tension. Verapamil blocked the increase in ionophore tension produced only by histamine. These results suggest that (i) calcium mobilization from the extracellular source alone can produce contraction comparable in magnitude to that induced by histamine or carbachol. (ii) Extracellular calcium mobilization through different pathways has a cumulative effect on human airway contraction.     

Use of muscle contraction formalism for kinesin in fast axonal transport.

The general procedure is discussed for calculating the velocity of a vesicle along a microtubule. The formalism used previously for isotonic contraction in muscle (with multiple actin sites for a given cross-bridge) can be employed. However, some modifications must be made: (i) the kinetic diagram must include a state in which kinesin is absent from a vesicle binding site, (ii) an average must be taken over the locations of the vesicle binding sites relative to microtubule sites, and (iii) a self-consistency condition must be imposed that equates the mean force exerted by kinesin molecules on the vesicle with the frictional resisting force of the medium.