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Regression analysis corroborated the trend towards an increase in the units firing rate and the muscle contraction velocity occurring in diminishing of the mammals' body mass. These relationships seem to be universal and can be the basis for explanation of the reverse dependence of basal metabolism on the body size.
As the spawning migration of the eel is supposed to correspond to a long swimming activity at depth, patterns of slow red muscle contraction have been investigated in European silver eel (Anguilla anguilla L.) exposed for 3 weeks to 10.1 MPa hydrostatic pressure. The results show that pressure-acclimated eels (male and female) show a three-fold decrease in maximum isometric stress of twitch and tetanic contractions while time to peak force, time from peak force to 90% relaxation and ratio of twitch tension to tetanic tension remain unchanged. The observed modifications in slow red muscle mechanical properties do not impede the spawning migration of the eel and are possibly partially compensated by an improvement in the efficiency of oxidative phosphorylation. Effects of changes in membrane fluidity are also discussed.
The effect of stimulating peripheral and central neural pathways on the electromyographic activity in the hyopharyngeal, thyropharyngeal, and cricopharyngeal muscles was studied in eight dogs during 1) eating, 2) unilateral electrical stimulation of the superior laryngeal nerve, and 3) unilateral electrical stimulation of the solitary nucleus. The duration of pharyngeal swallowing was significantly shorter during eating than during stimulation of the solitary nucleus in the anesthetized dog (mean difference 127 ms, SEM 9, n = 15). The duration of pharyngeal swallowing was significantly shorter during eating than during stimulation of the superior laryngeal nerve in the awake dog (mean difference 84 ms, SEM 13, n = 9). The duration of pharyngeal swallowing during stimulation of the superior laryngeal nerve under anesthesia was significantly shorter than during stimulation of the solitary nucleus under anesthesia (mean difference 58 ms, SEM 18, n = 9). The difference in duration of pharyngeal swallowing during stimulation of the superior laryngeal nerve between the awake state and during anesthesia was not significant (mean 19 ms, SEM 14, n = 9). It was concluded that stimulation of peripheral and central neural pathways resulted in different pharyngeal muscle contraction timing during swallowing in dogs.
The effects of sodium salts of various bile acids on the contractile force and the electrophysiological properties of rat ventricular muscle were studied in vitro. Primary, conjugated, and secondary bile acids were studied in a concentration range of 10(-9)-10(-6) mol/l, which corresponds to concentrations found in the plasma of patients with cholestatic jaundice. In general, the bile acid induced a negative inotropic effect which was manifested as a reduction in active tension, maximum rate of tension activation, and maximum rate of tension relaxation. Twitch duration and time to peak tension were unaffected by the bile acids. The negative inotropism was associated with a reduction in ventricular action potential duration. Resting potential, action potential amplitude, and maximum upstroke velocity of phase 0 depolarization were unaffected. Voltage clamp experiments in rat ventricular myocytes demonstrated that sodium taurocholate decreased the slow inward current and slightly increased the outward potassium current. Hence, these effects on the membrane currents are probably responsible for the negative inotropic effect.
Lung compliance is generally considered to represent a blend of surface and tissue forces, and changes in compliance in vivo are commonly used to indicate changes in surface forces. There are, however, theoretical arguments that would allow contraction of airway smooth muscle to affect substantially the elasticity of the lung. In the present study we evaluated the role of conducting airway contraction on lung compliance in vivo by infusing methacholine (MCh) at a constant rate into the bronchial circulation. With a steady-state MCh infusion of 2.4 micrograms/min into the bronchial perfusate (perfusate concentration = 0.7 microM), there was an approximate doubling of lung resistance and a 50% fall in dynamic compliance. There were also significant decreases in chord compliance measured from the quasi-static pressure-volume curves and in total lung capacity and residual volume. When the same infusion rate was administered into the pulmonary artery, no changes in lung mechanics were observed. These results indicate that the conducting airways may have a major role in regulating lung elasticity. This linkage between airway contraction and lung compliance may account for the common observation that pharmacological challenges given to the lung usually result in similar changes in lung compliance and airway conductance. Our results also suggest the possibility that the lung tissue resistance, which dominates the measurement of lung resistance in many species, might in fact reflect the physical properties of conducting airways.
Contractile filaments in skeletal muscle are moved by less than 2nm for each ATP used. If just one cross-bridge is attached to each thin filament at any instant then this distance represents the fundamental myosin cross-bridge step size (i.e. the distance one cross-bridge moves a thin filament in one ATP-splitting cycle). However, most contraction models assume many cross-bridges are attached at any instant along each thin filament. The purpose of this study was to establish whether the net filament sliding per ATP used could be explained quantitatively in terms of a cross-bridge model in which multiple cross-bridges are attached along each thin filament. It was found that the relationship between net filament sliding per ATP split and the load against which the muscle shortens is compatible with such a model and furthermore predicts that the cross-bridge step size is between 7.5 and 12.5nm over most of the range of loads. These values were similar for different muscle fibre types.
A new method was developed to compare patterns of coactivation and reciprocal activation of antagonistic muscles during different experimental conditions. Pure coactivation was defined as a muscle activity pattern where there was never a difference between the slope of the agonist EMG record and the slope of the antagonist EMG record. The degree of reciprocal activation was defined as being proportional to the average absolute value of the difference between these two slope values. Use of this method for the comparison of muscle activity patterns during isometric contractions and unexpected movements showed that peripheral input related to agonist unloading and antagonist stretch significantly increased reciprocal activity.
This review is the analysis of molecular mechanisms regulating the contraction activity of voluntary muscles. It summarises the data on muscle biochemistry for last decades. Literary and the author's data are devoted to the analysis of the following problems: ionic gradients of skeletal muscles; the energy origin for processes of the contraction initiation; the biochemical basis of electromechanical coupling; the role of a number of biologically active compounds in muscle functioning; regulatory aspects of the energetic supply of a contraction function; the change of muscle properties under the fatigue. The data given make possible to describe a single contraction cycle on the molecular level.
Spectral analysis of single-unit discharges, multi-unit EMG and muscle force during voluntary quasi-sinusoidal isometric contractions of two hand muscles revealed corresponding modulations of the firing rates of motor units at the frequency of the force oscillation. These rate modulations were correlated; and they showed a phase advance over the force oscillation, which is consistent with a cause-effect relationship between changes in firing rate and variations in force. These effects, observed over wide ranges of modulation amplitudes and frequencies, confirm the role of rate coding in the generation of time-varying muscle contractions; and they support the idea that during voluntary contraction of a given muscle, the motoneuron pool is subject to a common drive.
(1) The study investigated a possible involvement of protein kinase C (PKC) in the substance P-induced contraction of the longitudinal muscle of the guinea-pig isolated ileum. (2) The predominant effect of the PKC activator, phorbol-12,13-dibutyrate (PDB), was to change the time course of the response to substance P. While the initial peak contraction was hardly influenced by PDB, the fading of the contraction was accelerated to an extent that any tonic contraction which normally followed the initial peak response was prevented. This inhibitory effect of PDB on the tonic contraction was immediate in onset and related to its concentration (20-200 nM); responses to half-maximally (2-7 nM) or maximally effective (0.74 microM) concentrations of substance P were affected in the same manner. Tetrodotoxin (0.6 microM) did not alter the effect of PDB. Phorbol-13-monoacetate (2 microM), a phorbol ester which does not stimulate PKC, failed to change the time course of the substance P-induced contraction. (3) The tonic component of half-maximal contractile responses to histamine (0.2-0.4 microM) was also depressed by PDB (0.2 microM) whereas the tonic component of maximal responses to histamine (9 microM) was enhanced. (4) PDB (0.2 microM) reduced desensitization to substance P as judged by the reduction of the peak response to substance P (2-7 nM) following a 10-min exposure to a high concentration of the peptide (0.74 microM). (5) The PKC inhibitor, polymyxin B (0.1-0.3 mM), reduced the peak contractile response to substance P, slowed the fading of the contraction, and antagonized the inhibitory effect of PDB on the tonic contraction.(ABSTRACT TRUNCATED AT 250 WORDS)
BACKGROUND & AIMS: The increases in intraluminal pressure and muscle cross-sectional area (CSA) during esophageal contraction are markers of circular and longitudinal muscle contractions. The goal of our study was to determine temporal synchrony between circular and longitudinal muscle contraction in healthy subjects and patients with nutcracker esophagus. METHODS: Pressure and high-frequency intraluminal ultrasound (HFIUS) images were recorded simultaneously in healthy subjects and patients with nutcracker esophagus at 2 and 10 cm above the lower esophageal sphincter during wet swallow. HFIUS images were digitized and analyzed for the muscle CSA. The time interval (delta-t) between the peak muscle CSA and the peak pressure was determined. RESULTS: In healthy subjects, a close temporal correlation existed between the peak contraction pressure and the peak muscle CSA with a maximum delta-t of 0.5 seconds at the 2- and 10-cm levels (0-0.5 seconds). On the other hand, the patient group had a median delta-t of 1.25 seconds (0.75-3.5 seconds) at the 2-cm level and 0.75 seconds (0-2.0 seconds) at the 10-cm level. Ninety-eight of 103 contractions in patients showed a delta-t >0.5 seconds. There was a significant correlation between delta-t and the amplitude of pressure wave, the duration of pressure wave, and the peak muscle CSA. The duration of pressure wave but not the duration of CSA wave was longer in patients with nutcracker esophagus as compared with healthy subjects. CONCLUSIONS: Patients with nutcracker esophagus show temporal asynchrony between the contractions of circular and longitudinal muscle layers.
This report describes the actions of the non-peptide ergot alkaloids methysergide, methylergometrine and ergometrine at two types of 5-HT receptor mediating vascular contraction; the well established 5-HT2 receptor in rabbit aorta and a non-5-HT2 receptor in rabbit saphenous vein which resembles the 5-HT1-like receptor in dog saphenous vein. In the rabbit aorta ergometrine (1 mumol/l) and methylergometrine (0.3 mumol/l), but not methysergide, produced small contractions (14% and 7% respectively of the maximal response to 5-HT). This contraction was not related to activation of 5-HT2 receptors since it was resistant to blockade by ketanserin (0.3 mumol/l). When examined as antagonists of 5-HT-induced contractions of rabbit aorta, each ergot displayed nanomolar affinity at the 5-HT2 receptor but only methysergide behaved as a simple competitive antagonist (pKB = 8.25). Methylergometrine and ergometrine produced surmountable blockade which was accompanied by a non-parallel displacement of the 5-HT concentration-effect curves. The selective 5-HT1-like receptor agonist GR43175 (less than or equal to 30 mumol/l) was devoid of affinity at the 5-HT2 receptor in rabbit aorta. In the rabbit saphenous vein each of the ergots produced concentration-dependent contractions which resulted in overtly biphasic concentration-effect curves. Only the first phase of contraction mimicked the effects of 5-HT and GR43175 since contractions were not blocked by MDL 72222 (1 mumol/l), but were surmountably antagonised by methiothepin (10 nmol/l), ketanserin (0.3 mumol/l) and spiperone (0.3 mumol/l).(ABSTRACT TRUNCATED AT 250 WORDS)
Motor evoked potentials (MEPs) elicited by transcranial magnetic stimulation (TMS) and transcranial electrical stimulation (TES) of the motor cortex were recorded in separate sessions to assess changes in motor cortex excitability after a fatiguing isometric maximal voluntary contraction (MVC) of the right ankle dorsal flexor muscles. Five healthy male subjects, aged 37.4 +/- 4.2 years (mean +/- SE), were seated in a chair equipped with a load cell to measure dorsiflexion force. TMS or TES was delivered over the scalp vertex before and after a fatiguing MVC, which was maintained until force decreased by 50%. MEPs were recorded by surface electrodes placed over quadriceps, hamstrings, tibialis anterior (TA), and soleus muscles bilaterally. M-waves were elicited from the exercised TA by supramaximal electrical stimulation of the peroneal nerve. H-reflex and MVC recovery after fatiguing, sustained MVC were also studied independently in additional sessions. TMS-induced MEPs were significantly reduced for 20 min following MVC, but only in the exercised TA muscle. Comparing TMS and TES mean MEP amplitudes, we found that, over the first 5 min following the fatiguing MVC, they were decreased by about 55% for each. M-wave responses were unchanged. H-reflex amplitude and MVC force recovered within the 1st min following the fatiguing MVC. When neuromuscular fatigue was induced by tetanic motor point stimulation of the TA, TMS-induced MEP amplitudes remained unchanged. These findings suggest that the observed decrease in MEP amplitude represents a focal reduction of cortical excitability following a fatiguing motor task and may be caused by intracortical and/or subcortical inhibitory mechanisms.
To understand the underlying mechanism of ethanol in tonic contraction, the effect of ethanol on phospholipase A(2) and phospholipase C activities and the effects of phospholipase inhibitors on ethanol-induced contraction of cat gastric smooth muscle were tested. Circular muscle strips (2.0 x 0.2 cm) obtained from the fundus of cat stomach were used to measure isometric contraction. Ethanol elicited tonic contraction and activated phospholipase A(2) activity in a dose-dependent manner. Phospholipase A(2) inhibitors, manoalide (0.1--10 microM) and oleyloxyethyl phosphorylcholine (1--10 microM), significantly inhibited ethanol-induced contraction. Furthermore, 342 mM ethanol-induced contraction was significantly inhibited by cyclooxygenase inhibitors, ibuprofen (10--100 microM) and indomethacin (10--100 microM), but not by lipoxygenase inhibitors. On the other hand, phospholipase C inhibitors had no effect on ethanol-induced contraction, indicating that phospholipase C is not involved in ethanol-induced contraction. It is suggested from the above results that ethanol-induced contraction in cat gastric smooth muscle is, in part, mediated by phospholipase A(2) and cyclooxygenase pathways.
The purpose of this study was to evaluate the efficacy of the use of neuromuscular stimulation (NMS)-induced contraction of the paralyzed muscles to produce an active muscle pump for removing excess fluid and compare its effect with elevation of the upper extremity. The effects of 30 minutes of NMS of the finger and wrist flexors and extensors were compared with the effects of 30 minutes of limb elevation alone. Each of eight cerebrovascular accident (CVA) patients with visible hand edema received both treatments, one on each of 2 consecutive days. Measures of hand and arm volume and upper and lower arm girth were taken before and after each treatment. Analyses comparing mean percentage change scores for both treatments showed large and significant treatment effects for all dependent measures. The finding suggests that NMS was more effective for reduction of hand edema than limb elevation alone for this sample of eight CVA patients.
Healthy males (23-29 years) volunteered as subjects. We studied the ventilatory response to carbon dioxide and to isometric exercise (50% of maximum voluntary contraction) after administration of propranolol (20 mg), mepindolol (5 mg), salbutamol (20 mg) and placebo (single dose orally). The increase of pulmonary ventilation (VE) activated by central (CO2) and reflex stimulus (hand-grip) did not differ statistically between the four drugs. Analysis of VE in terms of inspiratory drive (Vt/Ti) and timing ratio (Ti/Ttot) showed that during CO2 stimulation mepindolol and salbutamol increased VE predominantly by the increase of Vt/Ti, presumably through the direct stimulation on the respiratory center. During rebreathing, Ti/Ttot increased significantly after administration of placebo and propranolol, so VE increased by a rise of Vt/Ti and by an increase of an effective 'timing component' (Ti/Ttot). Propranolol does not modify the ventilatory response to CO2 and hand-grip when VE is analyzed in terms of Vt/Ti and Ti/Ttot.
The relaxation and contraction in vertebrate skeletal muscle are regulated by Ca2+ through troponin and tropomyosin, which are located in the thin filament. Troponin is composed of three components, troponins C, I and T. In this review article, the Ca2+ -regulatory mechanism is discussed with particular reference to the regulatory properties of troponin T.
Phasic contractions of the hindlimb muscles were induced in hypercapnia, hypoxia and hyperoxia. Absolute value of the lung ventilation and its kinetics depended on hypoxic and hypercapnic stimuli, reaching its maximum in their combination. Hypoxic stimulus decreased an increment of the lung ventilation and decelerated the latter's development. The interaction seems to be realized by neuronal mechanisms of dorsal respiratory nucleus. The latter is believed to play a major role in the mechanism of generation of central inspiratory activity based on respective chemoreceptor and proprioceptor afferent information.