Drop In Tension Research Articles

Non-linear summation of tension in motor units of toad slow muscle.

Tension developed by single motor units and bundles of motor units has been recorded from the slow, non-twitch portion of the iliofibularis muscle of the toad Bufo marinus. Evidence was sought for the presence of individual muscle fibres within a motor unit which remained less than fully activated when the axon was maximally stimulated, i.e. at a rate and duration sufficient to produce maximum tension. When two motor units were stimulated separately and together, one at a low rate and the other at a maximal rate, the tension recorded on combined stimulation was greater than the sum of individual tensions, i.e. combined stimulation acted to 'facilitate' tension in a proportion of fibres. Adding the anticholinesterase eserine to the solution bathing the muscle produced a large increase in individual motor unit tensions but a rather smaller increase during combined stimulation of several axons. This suggested that in normal solution, maximally stimulating a single axon left many muscle fibres less than fully activated. When the local anaesthetic lignocaine was added to the bathing solution, tension in response to nerve stimulation fell, presumably because of impulse blockade in small terminal branches of the axon. However tension fell more steeply for single motor units than for combinations of motor units, again, we propose, because single motor units contain a larger fraction of incompletely activated fibres whose tension output depends critically on the level of activation. Overlap between two motor units is a measure of the proportion of fibres innervated by both axons. When overlap was measured over a range of different muscle lengths and using contractions of different durations, evidence was obtained in support of the notion that tension output of some muscle fibres was less than maximum not only because the fibre received too sparse an innervation to achieve a sufficient over-all level of depolarization but because they had been non-uniformly activated, leading to internal motion within the fibre and a consequent further drop in tension.

Superfast tension transients from intact muscle fibres.

We have measured tension transients from tetanically stimulated intact single fibres of the M. lumbricalus and the M. tibialis anterior of the frog. The measurements were carried out between 5.5 and 7 degrees C at a sarcomere length of 2.1 and 3.1 micron with a displacement servo system capable of performing displacements of 50 micron in 40 microseconds. We found a very fast recovery process in the tension transients thus obtained and quantified the speed of the observed recovery process in terms of elasticity and damping. If a ramp-shaped input signal of 150 microseconds duration is applied to the system, the velocity is constant over about 100 microseconds. This property of the system enables us to study the velocity-dependent part of the initial drop in tension in more detail. The first part of the tension transients thus obtained, show three phases: an initial rapid drop in tension, a slower steady decrease in tension and a rapid recovery (30 microseconds).

Ultraviolet and infrared effects on lattice gauge theories

High statistics Monte Carlo data using improved action à la Symanzik show an increase of the scaling window towards the strong coupling region, with respect to the standard action. Infrared behavior effects are analyzed; finite size effects show up in a sudden drop in the string tension which is more marked for the improved action.

Variation of levels of mRNA coding for antenna and reaction center polypeptides in Rhodopseudomonas capsulata in response to changes in oxygen concentration.

The effect of oxygen tension on the transcription of genes coding for the photosynthetic apparatus of Rhodopseudomonas capsulata was determined by the Southern hybridization technique. Restriction endonuclease digests of the R-prime plasmid pRPS404 and a subcloned fragment thereof served as DNA probes for genetically defined regions. The results showed that transcripts corresponding to the genes for certain pigment-binding polypeptides increase in amount by about 40-fold after a drop in oxygen tension. Transcripts hybridizing to genes involved in bacteriochlorophyll biosynthesis increase to a much lesser extent, and several genes involved in carotenoid biosynthesis are not affected by pO2.

Connecting filaments, core filaments, and side-struts: a proposal to add three new load-bearing structures to the sliding filament model.

This report concerns structural forces in resting muscle and proposes three additions to the sliding filament model to account for these mechanical properties. The proposal includes: connecting filaments (C-filaments) which connect the ends of each thick filament to the neighboring Z-lines, core filaments which support the myosin of the thick filament and which attach to the C-filaments, and side-struts which bind the thick filaments together along their length and restrict their radial movement. C-filaments would act as the parallel elastic element and transmit the passive tension to the thick filaments. Isolated myofibrils (mechanically-skinned and detergent-treated frog semitendinosus fibers) when stretched progressively showed exponentially-increasing passive tension which did not disappear when filament overlap was exceeded, but continued to rise. SL was monitored with a HeNe laser. Passive tension phasically exceeded 3 X 10(5) N/M2. Electron microscopy (thin-sectioned and freeze-fracture/deep-etch specimens) of non-overlap fibers showed orderly fibril structure with clear separation of A- and I-bands. In the gap between them could be seen filaments, 40-50 A in diameter, connected to the thick filament ends. Unlike actin, these filaments did not become decorated by myosin S-1. Equatorial X-ray measurements showed that stretching relaxed skinned muscles squeezed the thick filaments closer; this radial compression continued beyond filament overlap. Extreme stretch of fibers caused the thick filaments to strain several-fold. Treatment of non-overlap fibers with a high ionic strength pyrophosphate myosin solvent caused a large drop in passive tension and stiffness, but no change in SL was detected nor was myofibril continuity detectably affected. Non-overlap fibrils, when treated with elastase, released A-segments which retain three-dimensional coherency . Deep-etch EM's of non-overlap fibers disclosed abundant structures (about 75 A) wide attaching adjacent thick filaments.

Stoichiometric uptake of molecular oxygen and consumption of sulfhydryl groups by neocarzinostatin chromophore bound to DNA.

In the presence of DNA, and under conditions which resulted in efficient DNA degradation, the reaction of the neocarzinostatin chromophore with sulfhydryl groups was accompanied by a rapid drop in the oxygen tension of the solution. The total extent of oxygen uptake indicated that, consistently, 1 mol of O2 was consumed/mol of chromophore. The rate of oxygen uptake, however, was strongly dependent on the sulfhydryl concentration, and uptake occurred within a few seconds of the sulfhydryl-induced increase in 420-nm fluorescence of the chromophore. Parallel experiments, in which the sulfhydryl concentration of the solution was monitored, showed that approximately 2 mol of sulfhydryl groups were consumed/mol of chromophore, with kinetics similar to those of O2 uptake. Under anaerobic conditions, only 1 mol of sulfhydryl was consumed, but the sulfhydryl-induced fluorescence increase was not inhibited. These results suggest that (i) a reaction with a single sulfhydryl group converts the chromophore to an activated form, (ii) in the presence of DNA this activated chromophore participates in a subsequent reaction which consumes 1 mol of O2 followed by an additional mole of sulfhydryl, and (iii) each chromophore molecule undergoes only one such reaction cycle. In the absence of sulfhydryl groups, the chromophore slowly degraded, giving a product with intense 490-nm fluorescence. This spontaneous degradation reaction, which does not result in DNA damage, was also accompanied by uptake of nearly 1 mol of O2/mol of chromophore.

Short-range elasticity after tetanic stimulation in single muscle fibres of the frog.

The time course of the stiffness during the relaxation period following tetanic stimulation was studied in isolated single muscle fibres of the frog. The stiffness was measured by subjecting the fibres to a sudden stretch at constant velocity from an initial sarcomere length of 2.2 microns, and related to the tension carried by the muscle fibre immediately before the stretch. Both stiffness and tension fell close to the resting level during the first second (4 degrees C) after the end of stimulation. While stiffness and tension fell proportionally during the phase of almost exponential decline in tension following the shoulder in the tension recording, the relative drop in stiffness was less than the relative drop in tension during the preceding phase of almost linear decline in tension corresponding to the first 300-400 ms after the end of stimulation.

The dependence of the latency relaxation on temperature in single muscle fibres of the frog.

The time course of the latency relaxation was studied at various temperatures in the range 0-26 degrees. Over the entire range the time of onset of the drop in tension, t1, was independent of sarcomere length. At temperatures above 12-15 degrees C the falling phase had a point of inflexion, while at lower temperatures there was an interval during which the tension fell at a constant rate. The time when the rate of drop in tension had passed its maximum value tL2, the time to the maximum drop in tension t2, and the time when the tension crossed the resting level t3, all showed linear dependence on sarcomere length in the range from 2.1 to 2.7-3.4 microgram. In this range the durations of the intervals tL2-t1, t2-t1, and t3-t1 were nearly proportional to the distance from the Z-line to the end of the zone of overlap between the thick and the thin filaments. This could be explained as the activation being a longitudinal process starting from the Z-line. The slopes (dt/dS) of the linear portions of the time variables t1.2, t2, and t3 in a time-sarcomere length (S) diagram all had the same dependence on temperature giving a Q10 of 1.75. Under the assumption that the activation process followed a diffusion of calcium from the Z-line region to the zone of overlap a diffusion coefficient was estimated. At room temperature it had a magnitude of about 1/20 of that for calcium chloride in water. It had a dependence on temperature corresponding to an Arrhenius activation energy of about 37 kJ/mol which is about twice the activation energy for a simple diffusion of calcium in water. The results can be interpreted in terms of the time course of the latency relaxation mainly reflecting a longitudinal diffusion of calcium ions in the sarcoplasm.

Increase of resistance to stretch during the latent period in single muscle fibres of the frog.

The time from stimulation to the first change of the extensibility in an isolated skeletal muscle fibre was measured by subjecting the fibre to a rapid, small stretch at various times during the latent period. The experiments were performed at constant temperatures in the range 1-16 degrees C. Irrespective of the temperature, the first increase of the resistance to stretch occurred after the onset of the latency relaxation. At a temperature or 10 degrees C and a sarcomere length of 3 microgram the resistance started to increase 5.5 ms after stimulation, i.e. 1.5-2 ms after the onset of the drop in tension, and then increased nearly linearly with time. Corresponding to the end of the latent period, i.e. when the tension recrosses the resting level, the amplitude of the response was about 1.5 times its resting value. There was an interval between the onset of increase f the resistance to stretch and the time when the rate of drop in tension had passed its maximum value. The results are compatible with the hypothesis that the latency relaxation arises from a minute lengthening of the thin filaments as proposed by Haugen & Sten-Knudsen, and that attachment and generation of force take place at separate steps of the cross-bridge cycle.

Dependence of force and immediate stiffness on sarcomere length and Ca2+ activation in frog skinned muscle fibres.

1. Skinned fibres prepared from semitendinosus muscle of the frog (Rana temporaria) by a modified Natori's method were suspended in ATP-salt solution (pCa 5, pH 6.7, 3°C). Isometric tension was studied as a function of sarcomere length (determined by laser diffraction) and stiffness was measured by recording tension changes in response to quick changes in length performed within 0.5 ms during Ca2+ activated contractions. 2. There was a sigmoidal relationship between contractile tension or stiffness and pCa. The threshold Ca ion concentration was 5×10−7 M at a sarcomere length of 2.2 μm and a little lower at larger sarcomere lengths (as also described by Endo 1972). At all sarcomere lengths peak tension was reached at about 10−5 M Ca2+. 3. The skinned fibres produced maximum tension at sarcomere lengths of 2.0–2.3 μm. With a further increase in sarcomere length, contractile tension decreased. The relation between tension and sarcomere length was linear up to 3.2 μm above which value the relationship ‘tailed’. 4. Quick releases in the range of 0.1–0.5%L0 applied during Ca2+ activation produced an immediate elastic fall in tension in phase with the length change followed by a quick recovery phase completed within about 10 ms. Conversely, a quick stretch produced an elastic increase followed by a rapid tension decay completed within about 8–10 ms. When the extreme tensions obtained during the length step were plotted versus the size of the length step, a force-extension diagram was obtained corresponding to the T1-curve of Huxley and Simmons (1973) which intercepted the length axis at about −8 nm/half sarcomere at all sarcomere lengths investigated. The slope of the linear portion of the T1-curve was taken to determine immediate stiffness which was proportional to tension when either sarcomere length or Ca2+ ion concentration were varied. 5. In conclusion tension and immediated stiffness are proportional to the extent of actin myosin filament overlap and hence to the number of possible crossbridges between thick and thin filaments. 6. At very low calcium ion concentrations (10−7 M) skinned fibres develop tension and become stiff when the Mg-ATP concentration is lowered (at constant [ATP] total) to values below 10−5 M. Under these conditions a quick release causes a drop in tension which is—as in the case of rigor—not followed by a fast recovery of tension. Again stiffness was independent of the direction and amplitude of quick length changes; but — as in the case of rigor — the stiffness to tension ratio was much higher than in Ca2+ activated contraction.

Electrical and mechanical activities of frog heart during energetic deficiency

Metabolic inhibition of frog heart by cyanide (3 × 10−3m) induced a drop in tension before any significant alteration occurred in the action potential or the slow inward current. The decline in electrical activity appeared later. After 20 min in cyanide solution at a time when both tension andIslow were reduced, the addition of adrenaline (5 × 10−7m) greatly increased the slow inward current whereas tension only exhibited a partial and slow recovery. In both types of experiment the absence of correlation between the amount of inward Ca2+ current and the tension suggested the existence of a regulatory mechanism other than this current. It was not possible to correlate the fall in tension (which was parallel to the drop in creatine phosphate) with the reduction in ATP. ATP only decreased during application of both cyanide (CN−) and iodoacetic acid (IAA). Quick-stretch and quick-release experiments, conducted during the tension which developed in the presence of CN− and IAA, showed that the mechanical activity did not result from Ca2+-activated tension but from rigor tension, implying a marked deficiency in local ATP. A shortage of the energy available for myofibrillar ATPase activity might be one explanation for the drop in peak tension during metabolic inhibition and the rise in resting tension observed after more severe inhibition might be a shortage of the energy-rich phosphates available for myofibrillar ATPase activity.

A new surface viscometer of high sensitivity. III. Stearic acid at the oil/water interface

In a theoretical section the hydrodynamic theory of the knife-in-wall surface shear viscometer is extended to the oil/water interface. The theory is restricted to laminar flow of a Newtonian interface undergoing shear strains only. In a subsequent experimental section, the theory is applied to absorption films of stearic acid at the cyclohexane/water interface. At a fixed concentration of stearic acid in cyclohexane, the interfacial shear viscosity is shown to vary as changes are made in either the pH of the aqueous substrate or the temperature of the system. As the hydrogen ion concentration decreases, the interfacial viscosity rises from pH 5.5 to a dramatic maximum at pH 9.0. At pH > 9.0 the interface rapidly becomes less viscous as the pH is further increased. The change in the interfacial state at pH 9 is also coincident with a precipitous drop in the interfacial tension. When the aqueous phase is held at pH 9.0 and the system slowly warmed, an abrupt decrease in the interfacial viscosity occurs at 21.7°C. This “melting” point proves to be quite reproducible and is independent of the direction of temperature change. At T < 21.7° C the interfacial viscosity exceeds the upper limit of the viscometer, whereas at T > 22.0° C the viscosity remains fairly constant with T.

Effects of diltiazem, a calcium antagonist, on regional myocardial function and mitochondria after brief coronary occlusion

The purpose of the study was to assess the effect of the calcium antagonist diltiazem on mechanical and mitochondrial function of ischemic myocardium of the dog. Persistent depression of developed tension following brief coronary occlusion was measured in anesthetized and thoracotomized dogs. The extent of persistent depression of developed tension during reperfusion depended on the duration of occlusion and also on the pressure-rate index during occlusion. Diltiazem prevented the marked drop in developed tension of the ischemic segment of the myocardium following 5 min or 10 min of coronary occlusion. The inactive optical isomer of diltiazem had no effect on developed tension before or after coronary occlusion. Depression of the state 3 rate of respiration of mitochondria observed following 10 min of occlusion of coronary artery was almost completely reversed by pretreatment with diltiazem. Diltiazem may reduce the damage of ischemic myocardium during occlusion by hemodynamic action of the drug, and possibly by preventing damage to mitochondria.

Physical chemical properties of solutions of bis‐quaternary ammonium bromides

AbstractThe physical chemical properties of a series of bisalkyldimethyldi‐ammonium polyoxyethylene bromides were studied by measuring the critical micelle concentrations as function of their molecular structure. The conductivity vs. concentration plots revealed the existence of two distinct discontinuities which were labeled CMC1 and CMC2. The CMC1 was always lower than the CMC2. The conventional surface tension vs. log concentration curve showed the classical sharp break which coincided with either the CMC1 or the CMC2, but failed to reveal the presence of both critical micelle concentrations in the same experiment. The existence of two CMC2 was attributed to the presence of the two charges localized in separated atoms. The CMC1 and CMC2 appear to follow an expression of the type CMC=A —Bn, where A and B are constants and n the number of carbon atoms present in the hydrocarbon long chain attached to the quaternary ammonium nitrogen. The CMCs appear to increase with the increasing number of oxyethylene residues up to a certain length of the polyoxyethylene chain. For most compounds there was a substantial drop in surface tension with the increasing concentration of the salt. However, some compounds containing only one oxyethylene residue showed practically no surface tension dependence on concentration although the critical micelle concentrations were apparent in the conductivity vs. concentration curve. The energy to transfer one methylene group from the aqueous to the micellar phase was found to vary from −0.57 kT to −0.84 kT. The alkylene oxylated bisquaternary bromides studied appear to have unusual physical chemical properties.

The thermodynamic potential for homogeneous nucleation in a two-dimensional lattice gas

The Bethe or quasichemical approximation, is applied to the two-dimensional, triangular lattice gas in order to compute the probability of liquid drop formation in a supersaturated vapor. Comparison is made with the classical theory of homogeneous nucleation of Becker and Doring. The probability is of the form ρl exp(−Δψ/kT), where ρl is the density of bulk liquid (instead of the density of supersaturated vapor, which appears in the classical theory) and Δψ is a potential which approaches the classical form in the large drop limit. The potential for well-characterized, compact drops does not exist for sufficiently small drops, which we interpret to mean that such drops do not exist in the supersaturated vapor. When the limiting compact drop size is smaller than the classically predicted critical drop, the classical theory holds; however, in the opposite case large discrepancies occur. The error increases with increasing degree of supersaturation. Surface tensions were calculated in the large drop limit, showing a significant drop in surface tension with increasing supersaturation.

The time course of the latency relaxation as a function of the sarcomere length in frog and mammalian muscle

In a comparative study the isometric twitch tension and the latency relaxation were correlated to the sarcomere length in frog and mammalian muscle, the latter only in the length range from 2.4 to 3.1 μm since at higher degrees of stretch the sarcomere lengths became increasingly non‐uniform along the fibres. The location of the triads in mammalian muscle fibres was examined by means of electron microscopy. During stretch the location of the triads was gradually changed from the overlap zone at sarcomere lengths below 2.6 to 2.7 jim to the I‐band at sarcomere lengths above 3.0 to 3.1 μm, their centres (T‐tubules) being equally distributed between the overlap zone and the I‐band at sarcomere lengths around 2.9 μm. In both types of muscle the maximum amplitude of the latency relaxation (of about equal relative size) occurred at a sarcomere length of about 3.1 μm; and both twitch tension and latency relaxation were dependent upon the presence of a zone of overlap between the thin and thick filaments. In neither of the two types of muscles did the time, t1, from stimulation to the onset of tension drop depend upon the sarcomere length. At room temperature (22oC) t1 was about 1 ms in mammalian muscle and 2 ms in frog muscle. In mammalian muscle the time, t2, from the stimulus to the maximum drop in tension and the time, t3, to positive tension development were both substantially uninfluenced by changes in sarcomere length in the range 2.4 to 2.9 μm, whereas in frog muscle both t2 and t3 increased linearly with increasing sarcomere length in the above range. These findings are discussed in the light of the different locations of the triads in frog and mammalian muscle. It is concluded that the theory of Sandow (1966)–extended by Mulieri (1972)–and that of Haugen &amp; Sten‐Knudsen (1976), which both have the virtue of being able to account for the increase of the latent period with stretch in frog muscle, also would be applicable to mammalian muscle provided that a time lag of 0.5 to 1.0 ms exists from the time of the binding of Ca2+‐ions to the troponin molecules inside the zone of overlap until the attached cross bridges start to move and develop tension.

Latency-relaxation in single muscle fibres.

1. Latency relaxation and twitch tension were recorded simultaneously in single isolated muscle fibres of Xenopus laevis. 2. During low frequency (0.6 or 1 pulse/sec) repetitive stimulation, three successive phases of twitch tension were observed: negative staricase (a slight drop in tension), positive staircase (about 15% increase in tension) and fatigue. At the same time the amplitude of latency relaxation decreased monotonically, and near the peak of positive staircase, the amplitude decreased almost to an undetectable level. 3. The application of caffeine (0.1--1.5 mM) increased peak twitch tension by 15--200%, but decreased the latency relaxation amplitude by 30--93%. 4. The application of Ca-release inhibitors, deuterium oxide and dantrolene sodium, caused a 43--89% decline in peak twitch tension but no change in latency relaxation amplitude. 5. The lack of correlation between changes in peak twitch tension and latency relaxation amplitude suggests that latency relaxation is associated with the mechanism which triggers Ca2+ relase rather than with Ca2+ release itself.

An effectiveness study of a relaxation training tape with hyperactive children

A relaxation tape was compared with a control tape for effectiveness in reducing muscle tension. The experimental tape, obtained commercially, consisted of instructions for Jacobson-type sequential tightening and loosening of muscles; the control tape consisted of boys' adventure stories. Twenty hyperactive boys, aged 7 to 13, listened to either the relaxation or the story tape daily for 2 weeks. Forehead muscle tension was measured periodically, with a 10-day post-test. We found a significant drop in muscle tension for both groups (average 34%) and no significant difference between them at any point. This suggests that, at least for children, relaxation tapes may be no more effective than recorded stories for inducing a state of physical relaxation.

Effect of hyperosmolarity on resting and developed tension in heart muscle.

Simultaneous changes in weight, tension, and electrical activity were studied in the isolated perfused rabbit heart when the Ringer solution perfusion fluid was made hypertonic by the addition of sucrose, urea, glycerol, ethylene glycol, or formamide. The typical responses to each of the molecules was an initial drop in weight and tension followed by a return toward the base-line level. A 0.4 M concentration of sucrose, urea, or glycerol reduced the weight to 40 +/- 4.6, 48 +/- 3, and 52.2 +/- 3% of the initial value, respectively. The tension was simultaneously reduced to 23 +/- 3.5, 31 +/- 2, and 41 +/- 4% of its initial value. The tension drop produced by the solutes tested was linearly related to the amount of water lost by the heart. The falling phases of both tension and weight loss were closely correlated phases of both tension and weight loss were closely correlated in time a magnitude and were both related to the effectiveness of a particular molecule to move water out of the cells. In contrast, the subsequent rising phases of tension and weight were not as well correlated in time and magnitude. Whereas for most of the molecules used, the tension recovery was incomplete; urea, in contrast, caused an overshoot of the control tension level, thus pointing toward a unique inotropic effect of this compound. Resting tension rose for both urea and sucrose but not for the other compounds.

Idiopathic pulmonary fibrosis. Clinical, histologic, radiographic, physiologic, scintigraphic, cytologic, and biochemical aspects.

Idiopathic pulmonary fibrosis is a fatal disorder that starts as an alveolitis and progresses to interstitial fibrosis. Correlative morphologic, physiologic, and biochemical studies in 29 patients have shown that the inflammatory process in best followed by serial bronchoalveolar lavage and 67 Ga citrate scanning, and the fibrotic process is best followed by quantitation of the exercise-induced drop in arterial oxygen tension per unit of oxygen consumed. Although biopsies in idiopathic pulmonary fibrosis seem to show increased amounts of fibrotic tissue, biochemical studies suggest that the disease is probably one of collagen rearrangement rather than collagen increase. Perhaps becasue of this, peripheral lymphocytes of these patients recognize collagen as "non-self" and, when exposed to it in vitro, produce lymphokines and cell lysis. The fibrotic process is probably irreversible, but the inflammatory and immune processes that cause it may be amenable to therapy if diagnosed early.