PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Isotonic Contraction”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,405 records · Page 78Linked to original sources
PubMed1972

Loss of the plateau of the cardiac action potential in hypertonic solutions.

The effect of hypertonicity on the electrical properties of vertebrate myocardial cells was studied in ventricular muscle fibers of guinea pig, cat, frog, and chicken. The latter two species do not have a T-tubule system, whereas the former two do. In hypertonic solutions (2 x isotonic) produced by addition of sucrose or excess of NaCl, cell diameter decreased and there was a slight hyperpolarization and decrease in action potential overshoot. In guinea pig and cat, the hypertonic solution caused a decrease in input resistance and the plateau of the action potential to disappear in some of the cells; contractions of the entire ventricle also became depressed. These effects were reversed by returning the muscle fibers to isotonic solution. Addition of 5 mM SrCl(2) to the hypertonic solution also caused the plateau component and contraction to reappear. In frog and chick cells, loss of the plateau component and contraction never occurred in hypertonic solution, and input resistance increased. Urea and glycerol hyperosmolarity (2 x) caused no loss of the plateau component or contraction. If the frog and chicken ventricular, and guinea pig atrial myocardial cells (all of which lack T tubules) were to serve as an adequate control for possible effects of hypertonicity on the surface membrane and on contractile proteins, then the results suggest that swelling of the T tubules of mammalian myocardial cells leads to loss of the plateau component.

Action Potentials↗
PubMed1996

Canine bronchial sustained contraction in Ca2+-free medium: role of intracellular Ca2+.

We evaluated whether cartilage was a source of Ca2+ and the possible role of Ca2+ recycling in the sustained bronchial contraction (SBC) induced by carbachol (Cch) in Ca2+-free medium. Canine first-order bronchi were studied with cartilage and epithelium (+CAR + EPI) and without these structures individually (-CAR + EPI and +CAR - EPI) or together (-CAR - EPI). After cartilage removal (-CAR - EPI or -CAR + EPI) Cch produced a transient contraction in Ca2+-free medium. Removal of the epithelium alone had minor effects on the magnitude of the SBC but increased the effect of removal of cartilage to diminish the SBC. Bronchial strips with cartilage were able to respond to Cch with lower Ca2+ concentrations (10-100 microM) than could dissected preparations. Preincubation with BAY K 8644 (30-1000 nM) or 60 mM KCl or -CAR - EPI tissues converted the transient contractions to Cch in Ca2+-free medium to sustained contractions. In microelectrode studies, 50 nM Cch induced membrane oscillations in solutions with 2.5 mM Ca2+ in bronchial preparations, plus or minus cartilage, and in undissected tissues in Ca2+-free medium but not in -CAR - EPI tissues. Preincubation with 1 microM BAY K 8644 in Ca(2+)-free medium restored these oscillations in -CAR - EPI tissues. The release of 45Ca2+ from cartilage was too rapid to provide a reservoir of Ca2+ to support multiple SBCs in Ca2+-free medium. Moreover, in the Ca2+-free medium (with 10 nM Ca2+ after tissue +CAR + EPI incubation) excitatory junction potentials rapidly disappeared. Addition of 1 microM nifedipine or 1 mM EGTA during the SBC of +CAR + EPI tissues produced complete relaxation. A transient contraction to Cch occurred with prior addition of nifedipine. Inhibition of the sarcoplasmic reticulum Ca2+ pump by tissue incubation with cyclopiazonic acid (CPA; 10 microM), or briefly with 1 mM EGTA significantly diminished the SBC induced by Cch in Ca2+-free medium. CPA and EGTA together abolished the Cch-induced SBC. Thus, cartilage plays a more complex role than as a Ca2+ reservoir to support the SBC induced by Cch in Ca2+-free solution; its removal affects the process supporting SBCs involving intracellular Ca2+ storage and Ca2+ entrance through voltage-dependent channels.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1976

Length-induced changes in activation during contraction. A study of mechanical oscillations in strontium-mediated contractions of cat and frog heart muscle.

The plateau phase of prolonged Sr-mediated contractions of preparations of cat and frog heart muscle was used to study the transient response to abrupt changes in load or length. An oscillatory response (total amplitude equal to or less than 5% Lmax) was obtained. Isotonic oscillations were less damped than their isometric counterparts, implying positive feedback and thus a causal role of the perturbation in length. Oscillation frequency was 2-3 HZ at 29 degrees C (Q 10, 2-3); it could be increased by epinephrine or caffeine, independently of their effects on extent of shortening; it otherwise changed as a generally constant function of the length at which the oscillation occurred, whether this was altered by changes in extracellular [Sr], frequency of contraction, or load (independent of the direction and magnitude of the preceding load step). Similar oscillatory responses were induced during Sr- or Ca-mediated contractures. Cat muscles showed an additional slower component to the oscillatory response. Transient augmentation of the velocity-length relationship after abrupt reduction in load, previously described for twitch contractions under certain conditions, appears to be analogous to the first phase of the oscillatory response studied here. Our findings indicate that the oscillation is not attributable to any mechanism intrinsic to myofilament interaction, but rather that it involves length-induced changes in the level of activation, probably mediated by Ca2+ or Sr2+. We conclude that length influences the level of activation during contraction of heart muscle.

Action Potentials↗
PubMed1985

Regulation of isometric force and isotonic shortening velocity by phosphorylation of the 20,000 dalton myosin light chain of rat uterine smooth muscle.

The regulation of isometric force maintenance and isotonic shortening velocity by phosphorylation of the 20,000 dalton light chain of myosin has been examined for potassium-depolarized rat uterine smooth muscle. Following a transient peak in myosin light chain (LC20) phosphorylation at 20 s of contraction (0.46 mol PO4/mol LC20), phosphorylation declined to a steady-state by 2 min (0.28 mol PO4/mol LC20) with no significant change from 2-90 min of contraction. Isometric force developed more slowly, reaching a maximum at 2 min with no further change out to 90 min. Lightly-loaded (0.1 F0) shortening velocity, like LC20 phosphorylation, increased initially to a peak of 0.034 L0/s at 20 s of contraction and then declined to 0.023 L0/s by 2 min. However, unlike LC20 phosphorylation and isometric force, shortening velocity decreased approximately 4-fold from 0.023 L0/s at 2 min to 0.006 L0/s at 90 min of contraction. Graded activation with reduced extracellular calcium was associated with proportional changes in steady-state isometric force and LC20 phosphorylation. Shortening velocity was also decreased with reduced calcium, however, unlike LC20 phosphorylation, the greatest changes in velocity occurred at low levels of developed force. Moreover, in contrast to the large reductions in shortening velocity observed during 90 min contractions where force and LC20 phosphorylation were unchanged, similar reductions in shortening velocity did not occur with graded activation in spite of significant (greater than 3-fold) decreases in both force and LC20 phosphorylation. These results suggest that factors other than light chain phosphorylation are involved in the regulation of isotonic shortening velocity during extended isometric contractions of uterine smooth muscle.

Animals↗
PubMed1976

Spectral analysis of spontaneous contractions of the isolated portal vein of rats.

The spontaneous contractions of segments of rat portal veins have been examined in vitro under isotonic and isometric conditions. The power density spectra of recorded time series lasting 10-60 min were calculated. The spectra usually consist of harmonic frequency components. Only during shorter periods of analysis (10 min time series) we sometimes found additional non-harmonic components. All frequency components are proportionally shifted by changes of the bath temperature according to an average Q10 of 2.0. Increase of the load decreases the frequency of the contractons. The results of the spectral analysi, indicating a preponderance of a single source of periodicity, were supported by direct evidence of a pacemaker region. By recording contractions after systematic dissections of the portal vein segment, we found that spontaneous activity is generated at the central end of the segment.

Animals↗
PubMedDate not supplied

[Nonisotonic spontaneous contraction waves in isolated single cardiomyocytes].

One-dimensional contraction bands propagating spontaneously in a cardiomyocyte are studied theoretically for three experimental situations: isotonic (zero load) regime, isometric regime, and a strong adhesive contact between the cell and a supporting surface. Possible role of such a contact in the development of the cell damage is discussed.

Animals↗
PubMed1977

Effect of isoproterenol on relation between maximal rate of contraction and maximal rate of relaxation.

The relaxing effect of two positive inotropic interventions was studied in the isolated rat heart beating at constant rate and perfused at constant coronary flow. Experiments were performed under isotonic or isometric conditions during heart perfusions with Ca2+, 3.5 X 10(-3) M, and with isoproterenol, 10(-7) to 10(-8) M. Changes induced in maximal velocity of contraction (+L or +T) and maximal velocity of relaxation (-L or -T) were analyzed as the ratio between both maximal velocities (+L/-L or +T/-T). For similar increments in the amount of the apex-to-base shortening or in developed tension during Ca2+ or isoproterenol perfusions, the effect on the maximal velocity of relaxation differed for each intervention. High Ca2+ perfusion increased velocities of contraction and relaxation proportionally without significant changes in their ratio. Isoproterenol increased -L or -T more than +L or +T and the ratio showed a significant fall both in isotonic and isometric experiments (+L/-L, -0.33 +/- 0.11 and +T/-T, -0.38 +/- 0.09; P less than 0.01). The relaxing effect of the beta agonist seems to be related to the activation of the protein kinase system since perfusions with dibutyryl 3',5'-cAMP had a greater effect on the relaxation of the hearts.

Animals↗
PubMed1995

Role of xanthine oxidase and leukocytes in postburn cardiac dysfunction.

BACKGROUND: Recent studies suggest that the cardiac dysfunction that occurs after a major burn is mediated by oxygen-derived free radicals. This hypothesis is based on the fact that superoxide dismutase and catalase, given with fluid resuscitation from burn injury, provided significant cardioprotection. STUDY DESIGN: In this present study, rats received either enteral allopurinol or tungsten-enriched diets to determine if xanthine oxidase mediates postburn defects in cardiac contraction and relaxation. Polymorphonuclear neutrophil (PMN) were depleted to examine the contribution of PMN-derived factors to postburn cardiac dysfunction. Rats were divided into eight groups: groups 1 to 6 received regular chow, and groups 7 and 8 received tungsten-enriched diets for 14 days before study. Groups 2, 4, 6, and 8 were given a third-degree burn comprising 43 +/- 2 percent total body surface area and were resuscitated with Ringer's lactated solution for 24 hours (4 mL/kg/percent burn). In group 2, burned rats received fluid resuscitation alone; in group 4 (n = 10), rats were given allopurinol, 10 mg/kg daily by gastric lavage for five days preburn, group 6 (n = 11) received vinblastine (0.75 mg/kg) four days preburn, and group 8 (n = 11) received tungsten-enriched diets for 14 days before burn; sham burn controls included vehicle-treated (n = 10), allopurinol-treated (n = 8), PMN-depleted (n = 8), and tungsten-fed rats (n = 11) (groups 1, 3, 5, and 7, respectively). RESULTS: Burn injury produced mild hypotension, hypothermia, bradycardia, and a significant decrease in left ventricular performance, despite aggressive fluid resuscitation (group 2). Allopurinol, tungsten-enriched diets, and PMN depletion partially attenuated burn-induced cardiac contractile dysfunction and improved left ventricular responsiveness to increases in preload, coronary flow rate and exogenous calcium. CONCLUSIONS: Our data suggest that xanthine oxidase-derived oxygen metabolites and PMN-derived mediators contribute to postburn cardiac contractile deficits.

Allopurinol↗
PubMed1976

Isometric and isotonic length-tension relations and variaitonsin cell length in longitudinal smooth muscel from rabbit urinary bladder.

Isometric and isotonic length-tension relations of longitudinal smooth muscle from rabbit urinary bladder were studied together with muscle cell length and tissue structure as revealed histologically. In vivo strip length at a bladder volume of 10 m1 is referred to as L10. The smooth muscle was relaxed by Ca2+-free solution and contracted by K+-high solution with different Ca2+-concentrations. Maximal active force, 12.5+/-0.4 N/cm2 (S.E., n =11), for wholestrips was attained at a length of 206+/-4% (S.E., n=5) of L10. Passive tension at this length was about 15% of total tension. After correction for amount of connective tissue, maximal active tension of pure muscle bundles was 19 N/cm2. Up to about 165% of L10 isometric and isotonic length-tension relations were identical; if the muscle was stretched beyond this, it failed to shorten isotonically to the same length as when contracting from a shorter starting length. This decreased shortening capacity was reversible if the muscle was shortened passively. The extent of shortening against zero load was dependent on degree of activation suggesting an internal resistance to shortening. A linear relationship was found between bladder radius and muscle cell length, indicating that no slippage occurs between the cells when the bladder is filled. Mean cell diameter in the nuclear regionat L10 was 7.2+/-0.2 mum (S.D.,n=10). Mean macimal active tension per cell was calculated to be 2.3-10(-6) N and occurred at a cell length of 655 mum.

Animals↗
PubMed1985

Storage and release of mechanical energy by active muscle: a non-elastic mechanism?

In frog muscle fibres, tetanically stimulated at a sarcomere length of about 2 micron, stretched at a velocity of 1 lengths-1 and released against a force equal to the maximum isometric, P0, a phase of rapid isotonic shortening takes place after release. As the amplitude of the stretch is increased from 1.5 to 9% of the initial length: (1) the amount of rapid isotonic shortening increases up to 9-10 nm per half sarcomere and (2) the stiffness of the fibre (an indication of the number of bridges attached) decreases to a value about equal to that measured during an isometric contraction. If a 5-10 ms delay is left between the end of stretch and release, the amount of rapid isotonic shortening increases to about 12 nm hs-1. A 300-500 ms delay, however, results in a decrease in rapid isotonic shortening to about 5 nm hs-1 and also results in a velocity transients against P0 that are similar to those described during release from a state of isometric contraction. It is concluded that the force attained after large, fast stretches is due to a greater force developed by each bridge and not to a greater number of bridges. After the elastic recoil (when the force is suddenly reduced to P0), these strained bridges are able to shorten by about 12 nm hs-1, suggesting that, during and immediately after stretching, they are charged to levels of potential energy greater than those attained in an isometric contraction.

Animals↗
PubMed1998

The effects of serial stretch loading on stretch work and stretch-shorten cycle performance in the knee musculature.

Training methods to optimize stretch-shorten cycle performance and an active muscle's ability to resist a sudden stretch (stretch work) and the relationship between the two have not been fully explored. The purpose of this study was to examine the effects of an 8-week strengthening program of serial stretch loading on stretch work and stretch-shorten cycle performance in the quadriceps and hamstring muscles. Thirty-one asymptomatic subjects participated in pre- and post-tests of maximum voluntary isometric contractions, stretch work and stretch-shorten cycle trials, and single-leg vertical jumps. The training portion consisted of progressively resisted isotonic single-leg squats. One leg exercised against an isotonic load with serial stretch loading, while the other leg exercised against isotonic load alone. Training resulted in strength gains in both legs indicated by the increase in weight lifted during training, but not by maximum voluntary isometric contractions. Vertical jump height increased in both legs. In the hamstring, stretch work decreased and stretch-shorten cycle performance increased in both legs. In the quadriceps, serial stretch loading intervention resulted in increased stretch-shorten cycle performance and no significant change in stretch work. The correlation between stretch-shorten cycle and stretch work was weak but significant. These findings suggest that the use of serial stretch loading could improve muscular performance and enhance a muscle's potential for dynamic stabilization.

Adult↗
PubMed2006

Intravesical glucidic capsaicin versus glucidic solvent in neurogenic detrusor overactivity: a double blind controlled randomized study.

AIMS: Many studies report the use of alcoholic capsaicin instillation to treat neurogenic detrusor overactivity (NDO) in spinal cord injured (SCI) and multiple sclerosis (MS) patients. However, poor tolerability due to the irritative effect of the ethanol solvent limits its use. Our study aimed to evaluate the efficacy and tolerability of a new formulation of capsaicin in a glucidic solution in a multicenter clinical trial. MATERIALS AND METHODS: Thirty-three patients (26MS/7SCI) suffering from urinary incontinence due to refractory NDO were prospectively enrolled in a double-blind placebo controlled study and randomized to capsaicin group (CG, N = 17) or solvent group (SG, N = 16). They respectively received an intravesical instillation of 100 ml capsaicin diluted in glucidic solvent (CG) or glucidic solvent alone (SG). Efficacy (voiding chart, maximum cystometric capacity (MCC)) and tolerability were evaluated on days 0 (D0), 30 and 90. RESULTS: On D0, groups were homogeneous. On D30, significant improvement of overactive bladder syndrome and an increase in MCC were shown in CG, whereas there were no improvement in SG. No significant improvement was shown on D90 in both groups. There were no significant differences between groups regarding prevalence, duration, or intensity of side effects, except for short duration pubic pain during instillation more often reported in CG (58.8%) than in SG (12.5%) (P < 0.01). CONCLUSION: This placebo controlled study using glucidic capsaicin confirms its short-term efficacy in NDO patients. Global tolerance of glucidic capsaicin appeared satisfactory. Long-term efficacy and tolerance of repeated glucidic capsaicin instillations need to be evaluated.

Adult↗
PubMed1994

Cryopreservation of the common carotid artery of the rabbit.

We describe experiments on the cryopreservation of the rabbit common carotid artery aimed at improving upon previous results. We describe the design of a double clamp which holds the artery during transportation and storage, preventing twisting, shortening, and collapse of the vessel. The device allowed perfusion with solutions as desired and markedly reduced the extent of endothelial loss during procurement and processing. We also studied the effects of three vehicle solutions; a modified Hanks' solution, a solution originally developed for the cryopreservation of smooth muscle (K-Pipes), and a solution designed for corneal endothelium (CP-Tes). The criteria used to make the assessments were smooth muscle contractility and the structure and function of the vascular endothelium. A new staining method for vascular endothelium (combining propidium iodide with silver nitrate) is described. We found that there was significantly more endothelial cell damage in rabbit carotid arteries frozen in Hanks' solution than in the other solutions, and the recovery of smooth muscle contractility was lowest in the Hanks' group. Arteries cryopreserved using CP-Tes as the vehicle solution showed less endothelial cell damage than arteries preserved with either K-Pipes or Hanks' solution, and these arteries also exhibited the greatest relaxation response to acetylcholine. We conclude that careful handling of the vessels is important; of the solutions studied, CP-Tes is preferred for the cryopreservation of rabbit carotid artery with Me2SO.

Animals↗
PubMed1994

Influence of perioperative storage solutions on long-term vein graft function and morphology.

It has been shown that suboptimal preparation of a vein graft prior to its insertion results in immediate morphologic and functional damage to the endothelial cells but not to the underlying smooth muscle cells. However, little is known about whether such perioperative injury to the vein grafts influences the subsequent development of intimal hyperplasia and smooth muscle cell contractility. This study examines the influence of storage in saline solution or Ringer's lactate on the development of intimal hyperplasia and vasomotor function in experimental vein grafts. Twenty-six New Zealand white rabbits had a carotid vein bypass graft performed after the veins had been immersed (15 minutes) in either heparinized saline solution (Sal; n = 13) or Ringer's lactate (RL; n = 13), and each group was harvested after 28 days for either histologic (n = 8) or functional studies (n = 5; four 5 mm rings/graft). Saline storage of the vein graft resulted in a 38% increase in the thickness of the intimal hyperplasia (113 +/- 2 vs. 83 +/- 2 microns, Sal vs. RL; mean +/- SEM; p < 0.05) without a change in medial thickness (87 +/- 5 vs. 86 +/- 8 microns, Sal vs. RL; p > 0.05). The two sets of vein grafts showed no difference in sensitivity to norepinephrine, serotonin, and bradykinin.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

Role of dual pacemaker mechanisms in sinoatrial node discharge.

We investigated whether in the sinoatrial node (SAN) there are two different pacemaker mechanisms and whether either one can maintain spontaneous discharge. These questions were studied by means of an electrophysiological technique and of blockers of different diastolic currents in rabbit and guinea pig isolated SAN. In SAN subsidiary pacemakers of both species, Cs(+) (5-10 mM) or high [K(+)](o) (10-12 mM) decreased the maximum diastolic potential, abolished diastolic depolarization (DD) at polarized levels (subsidiary DD), unmasked a U-shaped dominant DD at depolarized levels, but did not stop the SAN. In rabbit SAN, E4031 (1 microM) and d-sotalol (100 microM) did not stop discharge, but did so after block of subsidiary DD by high [K(+)](o) or Cs(+). In guinea pig SAN, in Tyrode solution E4031, d-sotalol or indapamide (100 microM) did not stop SAN discharge. In the presence of Cs(+) or high [K(+)](o) indapamide (but not E4031 or d-sotalol) stopped the SAN. Ba(2+) (1-5 mM) led to stoppage of discharge both in Tyrode solution and in high [K(+)](o) or Cs(+). Depolarization by blockers of DD unmasked sinusoidal fluctuations, which during recovery were responsible for resumption of discharge. We conclude that in rabbit and guinea pig SAN, two different pacemaker mechanisms (Cs(+)- and K(+)-sensitive subsidiary DD, and Cs(+)- and K(+)-insensitive dominant DD) can independently sustain discharge, but block of both mechanisms leads to quiescence. Abolition of dominant DD by blockers of I(K) is consistent with a decay of I(K) as the dominant pacemaking mechanism, I(Kr) being more important in rabbit and I(Ks) in guinea pig. Sinusoidal fluctuations appear to be an essential component of the pacemaking process.

Action Potentials↗
PubMed1988

Preservation of left ventricular ejection fraction during percutaneous transluminal coronary angioplasty by distal transcatheter coronary perfusion of oxygenated Fluosol DA 20%.

The cardioprotective efficacy of coronary perfusion during angioplasty was evaluated. Forty-two patients underwent transcatheter infusion of oxygenated Fluosol DA, 20% emulsion (FDA-20), a perfluorocarbon oxygen transport fluid, into the distal coronary artery during balloon inflations. Left ventricular function was continuously monitored by two-dimensional echocardiography, and left ventricular ejection fraction was quantitatively analyzed from the video record by an area-length method with a validated computer algorithm. Each patient had multiple nonperfused and perfused balloon inflations lasting more than 45 seconds. Nineteen of the 42 patients also received control solutions of oxygenated Ringer's lactate and nonoxygenated FDA-20. The ejection fraction of nonperfused sequences fell from a baseline value of 57 +/- 15% to 36 +/- 14% at 45 seconds of inflation time (p less than 0.0005). Falls of similar magnitude were seen in the lactated Ringer's and nonoxygenated FDA-20 perfused balloon inflations. The ejection fraction fall was associated with a 54% rise in end-systolic volume (p less than 0.0005) and a 4% rise in end-diastolic volume (p = ns) compared to baseline. Inflations perfused with oxygenated FDA-20 showed a 45-second, left ventricular ejection fraction of 53 +/- 13% (p = ns compared to baseline), which was significantly greater (p less than 0.0001) than the 45-second ejection fraction of the nonperfused, or control solution perfused sequences. Results indicate that the profound fall in ejection fraction occurring during percutaneous transluminal coronary angioplasty can be ameliorated by distal coronary perfusion with an oxygenated perfluorocarbon emulsion.

Adult↗