Simultaneous recording of circular and longitudinal muscle contractions of the canine jejunum

Summary A method has been developed for monitoring the mechanical activities of individual longitudinal and circular muscles in a 5 millimeters long segment of intact intestine in the anesthetized dog. The longitudinal contractions were recorded by means of a new movement transducer. The circular contractions were recorded simultaneously using a water-filled intraluminal balloon A precise separation of longitudinal and circular motor activities was obtained with this method. The two muscle layers manifested motor activity most of the time, but their contractions were out of phase. Phase locking was observed only during short periods of time. The contractions were then sequential, the circular one being first.     

神经肽Y刺激血管平滑肌增殖和losartan的干预作用

目的：搪塞神经肽Ｙ和肾素－血管紧张素系统之间的相互作用与高血压疾病发生之间的关系。方法：应用快速微量ＭＴＴ比色法和荧光免疫组化定量技术,观察神经肽Ｙ对体外２血管平滑肌细胞增殖活度和血管平滑肌细胞核细胞增殖的表达的影响以及血管临终素Ⅱ受体拮抗剂ｌｏｓａｒｔａｎ对其影响的干预作用,结果：神经肽Ｙ可刺激体外２血管平滑肌的增殖、使其增殖活度（ＭＴＴ－ＯＤ值）和细胞内核增殖怕（ＰＣＮＡ）的表达明显高于对照组     

Losartan对神经肽Y诱导血管平滑肌

目的:观察神经肽Y(NPY)与血管紧张素受体拮抗剂losartan对体外培养的血管平滑肌细胞(VSMC)中PCNA、PDGF、c-myc癌基因表达的影响,从分子生物学的角度探讨NPY在高血压、动脉粥样硬化发生中的作用和losartan的逆转作用。方法:应用荧光免疫组化定量技术(ACAS570共聚焦激光扫描显微细胞仪)。结果:NPY刺激VSMC增殖,使其PCNA、PDGF和c-myc癌基因的表达明显高于对照组;losartan则可逆转NPY对VSMC增殖的刺激作用,使PCNA、PDGF和c-myc癌基因表达的平均荧光值降低。结论:NPY促进VSMC的增殖,其作用与高血压的发生有关;而losartan对高血压的治疗作用可能与拮抗NPY对VSMC增殖的刺激作用有关。     

Comparison of VIP and beta 2-adrenoceptor-induced relaxations in the circular and longitudinal smooth muscle layers of the rat portal vein

The relative importance of VIP in reduction of vascular tone was studied in circular and longitudinal preparations of the VIP-innervated rat portal vein. Exogenous VIP inhibited the methoxamine-evoked contractures in the atropine-blocked preparations with a lower potency in the inner, circular (pD2 = 6.4 +/- 0.5, n = 6) than in the outer, longitudinal layer (pD2 = 7.7 +/- 0.1, n = 6). VIP was also a less efficient relaxant (intrinsic activity (alpha) = 0.60 +/- 0.16, n = 6) of the inner than of the outer layer (alpha = 1.00). The selective (salbutamol) and the non-selective (isoproterenol) beta 2-agonists completely relaxed the methoxamine contractures in both layers and the potency (isoproterenol) was higher in the inner (pD2 = 6.39 +/- 0.32, n = 6) than in the outer layer (pD2 = 5.67 +/- 0.34, n = 6). Plasma from the portal-mesenteric vein of anaesthetized, fasting rats contained 0.036 nM VIP (median, n = 17), that is, several orders of magnitude lower than the range of VIP concentrations relaxing the methoxamine contracted vein preparations via VIP receptors of the apamin-blockable category. The results support the hypothesis that alpha 1-adrenoceptor-induced contractions in the circular layer are predominately relaxed via beta 2-adrenoceptors while relaxation of the outer layer may occur via VIP receptors, probably activated by local release of the neuropeptide.     

Adrenergic and cholinergic induced contractions of tracheal smooth muscle in the rabbit as demonstrated by a new in vivo method

An in vivo tracheal muscle preparation in the rabbit was developed which enabled us to measure changes in the isometric tension of the trachealis muscle in response to electrical stimulation of autonomic nerves and to i.v. administration of autonomic agonists and antagonists. The preparation was very sensitive to injections of carbachol, and showed graded contractions to stimulation of the caudal end of the cut cervical vagus as frequency and strength of stimulation were increased. Stimulation of the rostral end of the cut cervical sympathetic nerve fibers produced contractions in all preparations. This effect was mimicked by the alpha-adrenoceptor agonist, phenylephrine. The effects of both sympathetic stimulation and phenylephrine were blocked by phentolamine and not inhibited by pretreatment with atropine or propranolol. Sympathetic stimulation produced contractions of the trachealis muscle whether the initial tone was normal or actively increased by carbachol, while adrenaline produced relaxation when the initial tone was high. Using this new in vivo trachealis muscle preparation in the rabbit, we could show that sympathetic stimulation produced contractions of the trachealis muscle. This effect is consistent with the existence of smooth muscle activating alpha adrenoceptors.     

Benextramine逆转神经肽Y下调人血管平滑肌细胞LDL-R的表达

目的:探讨benextramine对神经肽Y(NPY)人血管平滑肌细胞(hVSMC)低密度脂蛋白受体(LDL-R)表达影响的逆转作用。方法:应用荧光免疫组化和激光扫描共聚焦显微技术,定量检测hVSMC的LDL-R表达的变化。Benextramine(B组)浓度设为10^-5mol/L,NPY设10^-8mol/L(N1组)、10^-7mol/L(N2组)、10^-6mol/L(N3组)和10^-5mol/L(N4组)4个浓度,培养时间分别为6、12、24和48h。结果:对照组LDL-R表达的平均荧光值较高,介于2564-2649之间,且各时段间均无显著差异(P>0.05)。各NPY组LDL-R表达的平均荧光值均明显低于对照组和各benextramine组(P<0.05),介于1639-2512之间,其荧光值随NPY浓度增加而下降,N1-N4组分别平均下降15.64%、20.31%、22.58%和27.42%,呈现一定的剂量依赖效应;同时其荧光值也随NPY作用时间的延长而下降,在6、12、24和48h时间段分别平均下降11.24%、21.29%、23.04%和30.38%,亦呈现一定的时间依赖效应。各benextramine组(包括B组、B+N1组、B+N2组、B+N3组及B+N4组)的LDL-R表达荧光值介于2554-2631之间,与对照组间差异无显著(P>0.05),且与NPY作用浓度及时间无关(P>0.05)。结论:NPY能导致hVSMC的LDL-R表达下降,benextramine可逆转该作用。     

Influence of antimuscarinics on alpha-adrenoceptors in the female rabbit urethra

The effects of the tertiary amine atropine and its structural analogues homatropine and scopolamine, as well as the quarternary amine emeprone, were evaluated on noradrenaline (NA)-induced contractions of isolated female rabbit urethral ring preparations. In addition, the abilities of these antimuscarinics to inhibit ³H—dihydro—alpha—ergocryptine (³H—DHE) binding to alpha—adrenoceptors were studied on a crude membrane preparation from the female rabbit bladder base and urethra. Atropine and homatropine depressed the NA- induced contractions in a concentration-dependent way, whereas this was not seen with scopolamine. Emeprone 10^-5 10^-4 M augmented the contractions, an effect possibly attributable to a NA-uptake blocking effect. All antimuscarinics displaced specific ³H— DHE binding, the order of potency being atropine>homatropine>emeprone>scopolamine. In general a good correlation was seen between the binding and mechanical activity studies for atropine, homatropine and scopolamine, while this was not found for emeprone. It is concluded that alpha-adrenoceptor blockade by atropine can be observed at concentrations exceeding 10^-7 M. Scopolamine, showing alpha-adrenoceptor blocking properties only in high concentrations, may be used as an alternative for blockade of muscarinic cholinoceptors.     

Functional relationship of longitudinal and circular layers of the muscularis externa of the rabbit large intestine

1. The functional relationship of the longitudinal and circular layers of the muscularis externa of the rabbit large intestine has been studied in a flat preparation.2. Evidence is presented that mechanical activity can be recorded independently and simultaneously from the two muscle layers of the flat preparation. Such evidence accrues mainly from results obtained from the flat preparation in response to various drugs.3. During spontaneous rhythmic contractions and during the response to pelvic (parasympathetic) nerve stimulation, both layers show similar activity, never opposite or reciprocal activity.4. In this flat preparation, the mechanism controlling the level of sustained tension (i.e. ;tone') may be dissociable, within limit, from the mechanism controlling rhythmic contractions.     

Comparison of VIP and β2--adrenoceptor-induced relaxations in the circular and longitudinal smooth muscle layers of the rat portal vein

Comparison of VIP and β₂-_-adrenoceptor-induced relaxations in the circular and longitudinal smooth muscle layers of the rat portal vein. Acta Physiol Scand 130, 601–607. Received I I November 1986, accepted 26 February 1987. ISSN 00014772. Department of Physiology, University of Bergen, Norwegian Defence Research Establishment, Kjeller, Norway. The relative importance of VIP in reduction of vascular tone was studied in circular and longitudinal preparations of the VIP-innervated rat portal vein. Exogenous VIP inhibited the methoxamine-evoked contractures in the atropine-blocked preparations with a lower potency in the inner, circular (pD₂= 6.4±0.5, n= 6) than in the outer, longitudinal layer (pD₂= 7.7 ± 0.1, n = 6). VIP was also a less efficient relaxant (intrinsic activity (a) = 0.60 ±0.16, n = 6) of the inner than of the outer layer (a= I. 00). The selective (salbutamol) and the non-selective (isoproterenol) β₂-_-agonists completely relaxed the methoxamine contractures in both layers and the potency (isoproterenol) was higher in the inner (pD₂= 6.39 ± 0.32, n = 6) than in the outer layer (pD₂= 5.67 ±0.34, n= 6). Plasma from the portal-mesenteric vein of anaesthetized, fasting rats contained 0.036 nM VIP (median, n= 17). that is, several orders of magnitude lower than the range of VIP concentrations relaxing the methoxamine contracted vein preparations via VIP receptors of the apamin-blockable category. The results support the hypothesis that a₁-_-adrenoceptor-induced contractions in the circular layer are predominately relaxed via β₂-_-adrenoceptors while relaxation of the outer layer may occur via VIP receptors, probably activated by local release of the neuropeptide.     

Effects of neurotensin on electrical and mechanical properties of smooth muscles in longitudinal and circular layers of the guinea-pig ileum

Effects of neurotensin (NT) on the electrical and mechanical activities of longitudinal and circular muscles of the guinea-pig ileum were investigated using the micro-electrode and isometric tension recording methods. In longitudinal muscles, the resting membrane potential was not affected by NT (0.1–30 nmol/l), but NT did provoke the contraction when applied in concentrations over 1 nmol/l. TTX (0.1 mol/l) neither modified the resting membrane potential nor the contraction evoked by NT, under condition of pretreatment with - and -adrenoceptor blockers. In circular muscles, NT (over 0.1 nmol/l) consistently hyperpolarized the membrane and increased the ionic conductance. The hyperpolarization appeared with a transient hyperpolarization, which gradually declined with a long time course. Using apamin and various concentrations of Ca, the NT-induced hyperpolarization was classified into two subtypes; fast and slow. The former was composed of maximum hyperpolarization due to activations of the Ca independent K channel, and the latter was composed of late hyperpolarization, due to activations of the Ca dependent K channel. During the NT-induced hyperpolarization in circular muscles, the amplitude of non-adrenergic, noncholinergic inhibitory junction potential (i.j.p.) evoked by field stimulation was reduced. This reduction induced by 0.5 nmol/l NT was mainly due to hyperpolarization of the membrane, and that observed in a high concentration of NT (3 nmol/l) was directly involved in ionic mechanisms contributing to the generation of i.j.p. In circular muscles, NT (over 3 nmol/l) did relax the tissue pre-contracted with 17.8 mmol/l K, but NT (below 30 nmol/l) did not relax the tissue pre-contracted by 39.6 mmol/l K. The relaxation of the pre-contracted tissue induced by NT depended on the hyperpolarization induced by NT. The results indicate that NT has direct actions on muscle cells of both longitudinal and circular layers of the ileum. In longitudinal muscles, NT has no effect on the membrane potential but does produce contraction, while in circular muscles, NT activates the Ca independent and Ca dependent K channels and relaxes the tissue, by hyperpolarizing the membrane. The membrane response evoked by NT differs from that induced by the activation of non-adrenergic, non-cholinergic nerves.     

Regional distribution of alpha-adrenoceptor subtypes in the female rabbit urethra

The aim of the present investigation was to study the regional distribution of alpha-adrenoceptor subtypes in the female rabbit bladder base and urethra, using radioligand binding and mechanical activity studies. The binding studies performed on membranes prepared from the bladder base, and the proximal and distal part of the urethra, revealed that the number of alpha 1-adrenoceptors did not significantly differ between the three regions, whereas the number of alpha 2-adrenoceptors increased distally. The mechanical activity studies showed that noradrenaline and clonidine, but not phenylephrine, were more potent in the distal than the proximal part of the urethra. It is suggested that in the female rabbit urethra the lower EC50-value found for noradrenaline and clonidine in the distal as compared to the proximal part of the urethra, at least in part, is attributable to a higher number of postjunctional alpha 2-adrenoceptors in the distal than in the proximal urethra.     

Electrical basis of contractions in the muscle layers of the pig colon

Simultaneous in vitro measurements of electrical and mechanical activities were performed, using suction electrodes and force transducers, respectively, on longitudinal and circular muscle layers of the pig proximal colon. In addition, circular muscle strips were studied with the sucrose gap technique. Spontaneous activity was present in both preparations. In the circular muscle, slow waves with superimposed spikes occurred at a variable frequency, accompanied by phasic contractions. Longitudinal muscle preparations showed a different behavior. Regular appearance of distinct slow waves as described for the circular muscle did not occur. Instead, periods of membrane potential oscillations at a frequency of 41 cycles/min and a duration of approximately 12 s were observed in this layer. Most oscillations had superimposed spikes, and each period of oscillations was associated with a contraction. Spontaneous activity in the circular layer was myogenic in nature but susceptible to innervation and stretch. In contrast, an excitatory stimulus (acetylcholine or stretch) was a prerequisite for activity in the longitudinal layer. Cholinomimetics increased and adrenergic agents decreased the frequency of the slow waves and spiking activity and frequency and force of contractions in the circular muscle. Cholinergic agents increased the activity in the longitudinal muscle into continuous electrical oscillations with spiking activity and concomitant tonic contractile activity, whereas adrenergic agents abolished electrical and mechanical activity. Spontaneous release of acetylcholine occurred, partly due to regenerative activity of myenteric cholinergic nerves. In addition, tonic activity in the noncholinergic nonadrenergic inhibitory neurons decreased circular muscle tone.     

Tetrodotoxin-resistant contractions induced by electrical stimulation of bladder muscle from man, rabbit and rat

Isolated detrusor preparations from man, rabbit and rat were suspended in an organ bath and isometric tension was recorded. The preparations were stimulated electrically in the presence of Bay K8644 and nifedipine before and after neuronal blockade with tetrodotoxin. Transmural electrical stimulation produced frequency-dependent contractions in all preparations. Bay K8644 significantly increased and nifedipine decreased these contractions. TTX effectively suppressed the response to electrical field stimulation in all species. When Bay K8644 was added to TTX blocked preparations, the responses to electrical stimulation were partly restored in bladder strips from man and rat. No increase in response was seen in the rabbit preparations. However, if the extracellular K+-concentration was increased to 10 mM (which per se did not affect the response) Bay K8644 significantly increased the contractions. All responses elicited by electrical stimulation in the presence of TTX were abolished by nifedipine. It is concluded that if the bladder smooth muscle is exposed to factors that can increase its sensitivity to contractile agents, this may result in uncontrolled (unstable) bladder contractions. Such contractions may use the 'normal' transmitter substances, but may be triggered at a lower stimulus intensity than normal. As a non-specific increase in membrane excitability seems to be associated with an influx of calcium through voltage-sensitive calcium channels, calcium antagonists, together with agents specifically blocking relevant transmitter substances, would offer an effective therapy against the unstable bladder.     

Motor unit recruitment order during voluntary and electrically induced contractions in the tibialis anterior

 The recruitment order of motor units (MU) was compared during voluntary and electrically induced contractions. With the use of spike-triggered averaging, a total of 302 MUs with recruitment thresholds ranging from 1% to 88% of maximal voluntary contraction were recorded in the human tibialis anterior muscle in five subjects. The mean (±SD) MU force was 98.3±93.3 mN (mean torque 16.8±15.9 mNm) and the mean contraction time (CT) 46.2±12.7 ms. The correlation coefficients (r) between MU twitch force and CT versus the recruitment threshold in voluntary contractions were +0.68 and –0.38 (P<0.001), respectively. In voluntary contractions, MUs were recruited in order of increasing size except for only 6% of the cases; whereas, during transcutaneous electrical stimulation (ES) at the muscle motor point, MU pairs showed a reversal of recruitment order in 28% and 35% of the observations, respectively, when the pulse durations were 1.0 ms or 0.1 ms. This recruitment reversal during ES was not related to the magnitude of the difference in voluntary recruitment thresholds between MUs. It is concluded that if the reversal of MU recruitment observed during ES is biophysically controlled by differences in their nerve axon input impedance, in percutaneous stimulation at the motor point, other factors such as the size and the morphological organisation of the axonal branches can also influence the order of activation. Received: 24 May 1996 / Accepted: 30 September 1996