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PubMedDate not supplied

The contraction induced by calcium ions in isolated guinea-pig vas deferens.

1. When isolated guinea-pig vas deferens was pretreated with 0.01% sodium edetate in an isotonic sucrose medium and then transferred to an edetate-free sucrose medium, the addition of CaCl2 (1.1 to 35.2 mmol/l) induced a contraction. 2. The contraction was greatest when the CaCl2 was added soon after pretreatment with edetate, and decreased with increasing time, almost disappearing after 1 h. 3. When KCl (1.4 to 22.4 mmol/l) was added in place of CaCl2, the contraction was lowest soon after pretreatment with edetate, and increased with time; after 1 h, the effect, was 80.7% of that observed in a preparation that had not been pretreaated with edetate.

Animals↗
PubMed1985

Excitation-contraction coupling in crab muscle fibers with swollen T tubules.

Single crab (Callinectes danae) fibers were equilibrated with isotonic, high KCl solutions and were subsequently returned to the control saline. This caused marked swelling of the T tubules. Fibers treated with 100 mM KCl had a 2.5-mV residual depolarization, a 50% decrease in effective membrane resistance (Reff) and a 75% reduction in membrane time constant (tau m). These fibers exhibited large increases in membrane conductance upon depolarization and were inexcitable; membrane depolarization with current pulses elicited no contraction. The effects of the KCl treatment on membrane properties were not reproduced by treatment with high potassium gluconate solutions, which did not cause tubular swelling. Tetrabutylammonium (10 mM) or Ba ions (10-20 mM), but not tetraethylammonium (40-100 mM), Sr ions (15-70 mM), or procaine (1-8 mM) reversed the effects of the KCl treatment on Reff, tau m, membrane excitability, and excitation-contraction coupling. The time course of the Ba effects was consistent with the suggestion that the KCl treatment increases the K conductance of the tubular membranes, which in turn prevents the activation of voltage-dependent Ca channels located in the membranes of the T system. This results in inhibition of the Ca-dependent electrogenesis and consequently, the absence of contraction upon depolarization of the plasma membrane.

Animals↗
PubMed1994

Mechanisms of the inhibitory effect of ketamine on guinea pig isolated main pulmonary artery.

Although ketamine increases pulmonary vascular resistance of patients, an occasional decrease of resistance in animals and humans has been reported. In addition, ketamine has a direct relaxant effect on isolated smooth muscle. The effects of ketamine on the main pulmonary artery rings isolated from the guinea pig were studied to elucidate the underlying mechanism of the reported relaxant effect of this anesthetic on smooth muscle. Ketamine (10-250 micrograms/mL) caused a concentration-dependent shift to the right of CaCl2 concentration-effect curves on artery rings, suggesting an interference with Ca2+ metabolism. In Ca(2+)-free buffer, ketamine (10-250 micrograms/mL) did not affect the magnitude of epinephrine-induced contractions but inhibited dose-dependent BaCl2-induced contractions. These observations suggest that ketamine inhibits transmembrane Ca2+ influx but does not affect its release from intracellular stores or its binding to intracellular receptor sites on the contractile system. Ketamine (25-500 micrograms/mL) also caused equipotent concentration-dependent relaxation of epinephrine-induced contractions in the absence and the presence of monensin, a Na(+)-ionophore that dissipates the Na+ gradient across the cell membrane, and in Na(+)-free, sucrose-substituted buffer. Ketamine (25-500 micrograms/mL) also relaxed ouabain-induced contractions to the baseline, an effect that was significantly attenuated in the presence of ruthenium red, a Ca2+ adenosine triphosphatase (ATPase) inhibitor. The relaxant effect of ketamine (250-750 micrograms/mL) of epinephrine-induced contraction also was attenuated in the presence of 0.1 mM lanthanum chloride (La3+), an inhibitor of adenosine 5'-triphosphate (ATP)-dependent Ca2+ extrusion, and completely inhibited in the presence of 10 mM La3+.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

The recovery from the relaxant effect by ouabain and the metabolic dependency of K+ contractions in guinea-pig taenia coli.

1. Ouabain (2.5 x 10(-5) M) inhibited preferentially the tonic response to 40 mM K+ medium (containing enough Na+) without affecting the phasic in taenia coli. When 11 mM lactate was added to the medium (pH 6.5) in the presence of ouabain, the tonic phase to 40 mM K+ recovered markedly. 2. Ouabain (2.5 x 10(-5) M) did not affect the tonic tension in 152 mM K+ medium (Na+ 0 mM). However, ouabain inhibited the recovered tension by the addition of 50 mM Na+ in the 152 mM K+ medium. But ouabain failed to inhibit the marked recovered tension by the addition of 11 mM lactate which utilized, even in the absence of external Na+, in 152 mM K+ medium. 3. Ouabain partly inhibited the shortening to 40 mM K+ (containing enough Na+) at light load; however, it inhibited markedly the shortening at heavy load. 4. There is a possibility that ouabain inhibits active transport of glucose depending on external Na+ in taenia coli of smooth muscle. Ouabain could not inhibit the tension by lactate which utilized under conditions of independent on Na+. Furthermore, it is suggested that ouabain inhibits the contraction which depends on aerobic metabolism; however, it has only a slight effect on contraction which depends on aerobic metabolism; however, it has only a slight effect on contraction which was not so dependent on aerobic metabolism.

Animals↗
PubMedDate not supplied

Inhibition of EMG activity in isometrically loaded agonist muscle preceding a rapid contraction.

It was recently suggested that a premotion silent period in isometrically loaded agonist muscle reflects transition process in switching motor program from an isometric to an isotonic condition. To test this hypothesis we investigated changes in EMG activity of a biceps muscle during motor preparatory phase in an entirely isometric paradigm. Five healthy volunteers produced rapid isometric elbow flexions superimposed on a slightly sustained contraction during self-paced and reaction time conditions. In addition to surface EMG, single motor units were recorded in agonist muscle prior to a rapid contraction. Silent period was found in responses of three out of five subjects, whereas inhibition of some but not all tonically active motor units was observed in all studied subjects prior to the phasic EMG burst. Inhibition of motor unit activity occurred more often in self-paced than reaction time contractions. Our results indicate that inhibition is not always powerful enough to produce a complete electrical silence, and weaker inhibitory effects were observed as a declining number of firing motor units. We conclude that the silent period or depression of the EMG activity is associated with changes in motor program from tonic to phasic muscle activation and is not merely a consequence of changes from an isometric to an isotonic condition.

Action Potentials↗
PubMed1968

The Schultz--Dale reaction of the depolarized guinea-pig uterus.

1. The sensitized guinea-pig uterus contracted on addition of antigen (egg-albumin), even after it had been completely depolarized in an isotonic potassium sulphate solution.2. The contractile response of the depolarized preparation started at a later time after addition of the antigen, and had a smaller amplitude, than the Schultz-Dale contraction induced in the ordinary Ringer solution.3. A contracting substance was released from the depolarized uterus. The average histamine equivalent of this substance was 89% of the histamine concentration which reproduced the anaphylactic contraction and probably proportional to the mechanical response.4. The main component of the material released from the uterus in the ordinary Ringer was histamine. The material released from the depolarized uterus did not contain any demonstrable histamine activity.

Anaphylaxis↗
PubMed1978

The response of lymphatic smooth muscles to vasoactive substances.

A study was made of the isotonic response of bovine mesenteric lymphatics to several physiological vasoactive substances. Contractions of lymphatic smooth muscles were induced by serotonin (5-HT), prostaglandin F2alpha (PGF2alpha), noradrenaline (NA), histamine, dopamine and acetylcholine (ACh). The smooth muscles were particularly sensitive to 5-HT. Excepting PGF2alpha no other substances could equal 5-HT in the magnitude of the maximum response. The majority of 5-HT receptors seemed to be the D receptors. The decreasing order of the contractile responses was as follows: 5-HT greater than PGF2alpha greater than NA greater than histamine greater than dopamine greater than ACh. The contractile response to ACh was observed only in specimens involving valvular region. It was very likely that, in the lymphatics, there were 2 kinds of receptors for catecholamines, i.e. alpha and beta receptors, and the stimulation of the former induced smooth muscle contraction and that of the latter relaxation. A difference was noticed between the responses of valvular and intervalvular segments to NA. Relaxations of lymphatic smooth muscles were induced not only by isoproterenol but also by adenosine and adenine nucleotides. The decreasing order of the relaxant responses was as follows: ISP greater than adenosine greater than ATP greater than ADP greater cyclic AMP greater than or equal to AMP. The relaxant responses to adenine nucleotides tended to reduce with decrease in the number of high energy phosphates.

Adenine Nucleotides↗
PubMed1998

Vibration-induced postural posteffects.

It generally is known that vibration of various muscles in free-standing subjects evokes a spatially oriented postural response. Furthermore, it recently has been shown that when a vibratory stimulus is terminated, a powerful involuntary contraction of the previously vibrated muscle often occurs that, under the isotonic condition, is accompanied by movement of a limb. The aim of this study was to explore effects of a low-amplitude mechanical vibration, applied in a seated position, on the standing posture. The 30-s vibration was applied bilaterally at the ankle level to anterior or posterior tendons and at the cervical level in front or back of the neck, at one site only at a time. Center of pressure trajectories were monitored during quiet stance for </=19 min after the offset of vibration, and these measurements were compared with a previbration control trial. The results clearly indicate that vibration produced in all subjects strong, long-lasting dynamical modification of posture mainly in the anterior-posterior direction. Spatial orientation of the induced postvibratory shift in posture was dependent on the vibration side. We conclude that sustained Ia sensory inflow, evoked by vibration, has a powerful after-effect on the motor system at the postural level.

Adult↗
PubMedDate not supplied

Muscarinic receptor sensitivity in airway smooth muscle of patients with obstructive airway disease.

The hypothesis of an increased muscarinic receptor sensitivity in airway musculature of patients with asthma, chronic obstructive bronchitis and emphysema was investigated through methacholine-induced contraction of isolated airway smooth muscle strips. Contractile responses were recorded isotonically in tracheal smooth muscle preparations of 5 patients with chronic obstructive bronchitis, 2 patients with emphysema and 1 patient with allergic asthma, as well as in bronchial tissue preparations of 7 patients with chronic obstructive bronchitis. The responses were compared to those obtained in airway tissue preparations of 25 control subjects. The sensitivity to methacholine was normal in all groups of patients. This suggests that muscarinic receptor behaviour is normal in airway smooth muscle of patients with obstructive airway disease.

Aged↗
PubMed2006

Experimental muscle pain changes the spatial distribution of upper trapezius muscle activity during sustained contraction.

OBJECTIVE: To investigate the effect of local excitation of nociceptive muscle afferents on the spatial distribution of muscle activity. METHODS: Surface electromyographic (EMG) signals were recorded from the upper trapezius muscle of 10 healthy volunteers with a 5 x 13 electrode grid during 90-s isometric contractions before, during, 15 and 30 min after intramuscular injection of hypertonic (painful) or isotonic (non-painful) saline. From the multi-channel EMG recordings, two-dimensional maps of root mean square and mean power frequency were obtained. The centre of gravity of the root mean square map was used to quantify global changes in the spatial distribution of muscle activity. RESULTS: During sustained contractions, average root mean square increased, average mean frequency decreased and the centre of gravity moved cranially. During experimental muscle pain, compared to before injection, the average root mean square decreased and there was a caudal shift of the centre of gravity. Fifteen minutes after the painful injection the centre of gravity returned to its original position. CONCLUSIONS: Short-term dynamic reorganization of the spatial distribution of muscle activity occurred in response to nociceptive afferent input. SIGNIFICANCE: The study furnishes an extension of the pain adaptation model indicating heterogeneous inhibition of muscle activity.

Adult↗
PubMedDate not supplied

[Comparative assessment of contractility of different sections of the intestine (an experimental study)].

Contractility of different portions of the intestine used for partial or complete replacement of the bladder was studied on the circular fragments of non-inbred rats' intestine. The contractility was studied at rest, in response to electric stimulation, addition to the solution of growing concentrations of cholinomimetic or adrenomimetic drugs, to depolarization of smooth cell membrane with hypersodium solution. It was established that contractility of the large intestine contrary to that of the small intestine is characterized by diminished amplitude of spontaneous contractions. In addition of cholino- and adrenomimetics, amplitude of the phasic and tonic reactions in the large intestine fragments compared to those of the small one was decreased. The conclusion was made that the large intestine is preferable for taking transplants partially replacing urinary bladder to correct its reservoir function whereas small intestinal grafts are more suitable for total replacement of the detrusor.

Acetylcholine↗
PubMed1982

The pCa-tension and force-velocity characteristics of skinned fibres isolated from fish fast and slow muscles.

1. Single fast fibres and small bundles of two to six slow fibres were dissected from the myotomal muscles of the cod, Gadus morhua, and the dogfish, Scyliorhinus canicula. Fibres were chemically skinned with the non-ionic detergent Brij 58.2. The isometric tension properties were investigated. Maximal isometric tensions (mean +/- S.E. of mean) were 18.65+/-1.18 (n = 11) and 8.34+/-0.98 (n = 13) N cm(-2) for cod fast and slow fibres, and 18.34+/-0.88 (n = 28) and 8.24+/-0.39 (n = 12) N cm(-2) for dogfish fast and slow fibres respectively. The values are comparable to those observed in mammalian and amphibian skinned fibres. The lower tensions generated by the slow fibres cannot be fully explained on the basis of their lower myofibrillar fractional volume.3. In common with previous studies, a steep sigmoid relationship between pCa and tension was observed. The threshold for tension generation was around pCa 7.2. Half-maximal pCas were 6.08 and 6.42 for cod fast and slow muscle, and 6.41 and 6.50 for dogfish fast and slow fibres respectively. Cod fibres were maximally activated at around pCa 5.18, and dogfish fibres at pCa 5.62.4. Contraction-induced residual tensions were observed in cod fast fibres after return to relaxing solution. This phenomenon is a feature common to many skinned fibre studies, but the mechanism behind it has yet to be resolved.5. The force-velocity characteristics of fast and slow fibres have been investigated (at 8 degrees C).6. Points below 0.6 P(0) on the P-V curves could be fitted to a linear form of the Hill equation. Extrapolated V(max)s were calculated as follows: cod fast fibre V(max) = 1.01 muscle length sec(-1) (Lsec(-1)) (a = 0.21 P(0); b = 0.21 Lsec(-1)). Slow fibre = 0.53 Lsec(-1) (a = 0.28P(0); b = 0.21 Lsec(-1)). Dogfish fast fibre V(max) = 2.34 Lsec(-1) (a = 0.06 P(0); b = 0.14 Lsec(-1)). Slow fibre = 0.67 Lsec(-1) (a = 0.19 P(0); b = 0.13 Lsec(-1)).7. Contraction velocity in cod slow fibres decreased continuously to produce markedly non-linear velocity transients, similar to those reported for amphibian slow fibres.8. The effect of altering Ca(2+) concentration on the shape of the isotonic velocity curve (at low loads) was studied in dogfish fast fibres (0.5-1 degrees C). Contraction velocity decreased continuously during shortening, at both maximal and half-maximal Ca(2+) concentration. The rate of decay of velocity with shortening was greater at low Ca(2+) concentration.

Action Potentials↗
PubMed2001

The role of vagal efferents in regulation of gastric emptying and motility in rats.

UNLABELLED: Nonpharmacologic regulation of gastrointestinal motility may become competitive to actually applied methods in the nearest future. The Aim of this study was to evaluate effect of vagal stimulation on gastric motility and emptying. Experiments were performed on 30 male Wistar rats in vivo. Electrodes (120 um O Cr/Mo Microfil Industries) were placed on right vagal trunk below diaphragm without affecting its integrity. The fistula was implanted in gastric antrum. Stimulation parameters were: 0.3 V; 0.5 Hz, impulse duration--10 msec, time stimulation--5 min. Gastric pressure (balloon, Synectics pressure transducer, Sweden) and gastric emptying (red phenol method) were measured subsequently during and between stimulations. RESULTS: Stimulation significantly decreased amplitude of gastric contractions about 14% (52.7 +/- +/- 24.5 vs control 66.8 +/- 15.0; p < 0.05) and increased liquid gastric emptying from isotonic solution about 10% (87.35 +/- 4.75 vs control 75.31 +/- 11.24; p < 0.001), hypertonic liquid about 15% (49.05 +/- 12.16 vs control 34.1 +/- 13.68; p < 0.001) and hypotonic liquid about 7% (83.05 +/- 8.8 vs control 76.29 +/- 11.88). The frequency of gastric contractions did not change significantly in Fast Fourier Analysis of the period of stimulations and in control group. CCK concentrations were not significantly different between stimulated and control group (0.3 +/- 0.08 vs control 0.27 +/- 0.06 pmol/L). L-NAME infusion abolished completely acceleration of gastric emptying of isotonic solution (50.38 +/- 12.66 vc control 87.82 +/- 5.49; p < 0.05), hypertonic solution (32.17 +/- 15.09 vs control 51.65 +/- 10.74; p < 0.05) and hypotonic solution (60.42 +/- 12.05 vs control 82.67 +/- 8.06; p < 0.05) during electrical stimulation. DISCUSSION: In this experiment efferent stimulation of abdominal vagal nerve release neuromediators from afferent and efferent fibers. The main regulator seems to be nitric oxide. These results indicate the effective vagal nerve stimulation affects gastric motility and emptying. It is likely that observed effects reflect integrated response with activating vago-vagal reflexes and neurohumoral factors.

Animals↗
PubMed1966

Caffeine- and potassium-induced contractures of frog striated muscle fibers in hypertonic solutions.

The effect of hypertonic solutions on the caffeine- and KCl-induced contractures of isolated fibers of frog skeletal muscle was tested. Hypertonic solutions, twice the normal osmotic strength, prepared by adding NaCl or sucrose, potentiate the caffeine-induced contractures. The fibers may develop tensions of 3.6 kg/cm(2) of fiber transverse section. The same hypertonic medium reduced the peak tension of KCl-induced contractures. Thus the hypertonic condition does not affect the contractile mechanism itself. These findings give further support to the view that the differential effect of hypertonic solution is on the excitation-contraction coupling mechanism. Extracellular calcium is not essentially required for the first few of a series of caffeine-induced contractures either in hypertonic or in isotonic solutions.

Animals↗
PubMed1969

Cross-bridge properties derived from muscle isotonic velocity transients.

The rate constants for the turnover of cross-bridges during frog muscle contraction were determined from an analysis of the motion that follows step decreases in load. For a given projection from the myosin filament, there appears to be a range of about 100 A along the length of the filament over which the projection can attach to the actin filament and form a cross-bridge. The site of attachment is then displaced by a distance of this same order before the link is broken. The values of the rate constants also imply that a cross-bridge is formed each time an actin site comes within range of a myosin projection, so that the turnover of cross-bridges for a given contraction distance is independent of the speed of the motion.

Animals↗
PubMed1985

[Performance of the isolated perfused soleus muscle of the rat].

The energy expenditure at resting and in contractions was measured in the rat isolated m. soleus perfused with Krebs-Khenselite solution at 37 degrees C. The muscle exerted isotonic tetanus of 0.6-sec duration with 0.1-Hz frequency. The energy expenditure at resting was 18.5 mVt/kg of dry matter, that in contractions was linearly related to amount of work. The efficiency coefficient (the work increment-energy expenditure increment ratio) was on the average 24.5%. A part of the energy released in contractions (13.9 mVt/kg of dry matter) did not depend on the amount of work.

Animals↗