Oscillatory Work Research Articles

On the influence of adsorbates on heteroepitaxy: work function oscillations during deposition of copper on platinum (111)

In the present paper we show results of dynamical work function measurements during the growth of multilayer films of Cu on Pt(111). The obtained data show in the temperature range between 350–450 K a slightly temperature dependent work function decrease due to Cu deposition. Intermittant coadsorption of oxygen on a previously deposited Cu film of 2 ML thickness results in an oscillatory work function change (ΔФ) during further Cu deposition. The amplitude of the ΔФ oscillations depends significantly on substrate temperature and deposition rate. These experimental results are discussed in terms of a growth model which considers the influence of surface morphology on the work function via the so-called Smoluchowski effect.

Negative viscosity and nonlinear elasticity of muscle cross-bridges

Negative viscosity is found in active fibrillar insect flight muscle when it is stretched, and this nonlinear phenomenon of ‘stretch activation’ allows the muscle to perform oscillatory mechanical work. We show that stretch activation may be a consequence of quite simple cross-bridge kinetics. In the first place, we consider an elementary but instructive two-state model in which cross-bridge attachment depends on stretching a series spring by thermal activation. This model exhibits a mechanical yield point, and the elastic properties are nonlinear. In particular, we show that the two-state system becomes more lossy and unstable as the yield point is approached, although the loss remains positive, so the system cannot perform oscillatory work. A three-state model incorporating tilting of the attached cross-bridge represents the next step towards a more realistic cross-bridge model. Attachment and detachment at the start of the power stroke are treated as in the two-state model, and we assume that tilting is also thermally activated in a manner similar to that suggested by Huxley and Simmons. Detachment at the end of the power stroke is assumed to be completely irreversible, and it is therefore this one non-equilibrium step which is coupled to the ATP hydrolysis that drives the cross-bridge cycle. This simple three-state model displays many of the characteristics of fibrillar insect flight muscle.

Modeling red muscle power output during steady and unsteady swimming in largemouth bass

We recorded electromyograms of slow-twitch (red) muscle fibers and videotaped swimming in the largemouth bass (Micropterus salmoides) during cruise, burst-and-glide, and C-start maneuvers. By use of in vivo patterns of stimulation and estimates of strain, in vitro power output was measured at 20 degrees C with the oscillatory work loop technique on slow-twitch fiber bundles from the midbody area near the soft dorsal fin. Power output increased slightly with cycle frequency to a plateau of approximately 10 W/kg at 3-5 Hz, encompassing the normal range of tail-beat frequencies for steady swimming (approximately 2-4 Hz). Power output declined at cycle frequencies simulating unsteady swimming (burst-and-glide, 10 Hz; C-start, 15 Hz). However, activating the muscle at 10 Hz did significantly increase the net work done compared with the work produced by the inactive muscle (work done by the viscous and elastic components). Thus this study provides further insight into the apparently paradoxical observation that red muscle can contribute little or no power and yet continues to show some recruitment during unsteady swimming. Comparison with published values of power requirements from oxygen consumption measurements indicates a limit to steady swimming speed imposed by the maximum power available from red muscle.

Effect of temperature and stimulus train duration on the departure from theoretical maximum work in fish muscle

The goal of the present study was to compare the effect of temperature on contraction kinetic parameters of fish muscle with its effect on oscillatory work. In particular we studied the effect of stimulus train duration or duty cycle (the fraction of the imposed length change that the muscle was stimulated). We compared the actual work done by the muscle with a theoretical maximum work loop that would be achieved if it were fully and instantaneously relaxed at the onset of shortening and fully and instantaneously relaxed at the onset of lengthening. Temperature had a small effect on force but a marked effect on contraction and relaxation times. Thus, work was more temperature sensitive than force. The effect of temperature on work could not be predicted by its effect on any one contraction kinetic parameter. To achieve maximum work at lower temperatures, the duty cycle must be decreased because of the longer relaxation time.

Effect of stimulus duty cycle and cycle frequency on power output during fatigue in rat diaphragm muscle doing oscillatory work.

Isolated rat diaphragm muscle was stimulated repetitively to induce fatigue, and the work done during each contraction was measured. Work per cycle was calculated by measuring force as the activated muscle was subjected to sinusoidal length changes (from 97 to 103% of L0, where L0 is rest length). Work was calculated from the loop formed when force was plotted against length. Work done was positive when the muscle was shortening and was negative when it was lengthening; net work was the difference. Work output was varied by changing the stimulus duty cycle (4, 8, or 16% of the total cycle duration) and cycle frequency (1, 2, or 4 Hz). The rate and extent of the decrease in power was influenced much more by changes in cycle frequency than by changes in duty cycle. Duty cycle and cycle frequency combinations that resulted in greater power in the prefatigue trials were associated with a more rapid rate of fatigue. However, net positive power at the end of the 15-min fatigue period was greater under these same conditions (i.e., high duty cycle and high cycle frequency). Fatigue in working diaphragm muscle depends more on cycle frequency than on duty cycle.

Surfactant induced layer-by-layer growth of Cu on Ru(0001) as revealed by oscillatory work function changes

Dynamical work function change measurements (Δφ), during the growth of thin heteroepitaxial films, have been performed using a special Kelvin probe. As a model system the deposition of thin Cu films on Ru(0001) and, especially, the influence of preadsorbed oxygen as a “surfactant” for layer-by-layer growth was studied in a wide range of temperature and oxygen precoverage (θ O). For appropriate conditions ( T = 400 K, θ O ≈ 0.4 ML) the Δφ-curves exhibit a remarkable oscillatory behavior of high amplitude which is clearly resolved up to at least 80 periods, the limiting fact being mainly an inhomogeneous deposition. Each period is demonstrated to correspond to the deposition of just one complete Cu layer clearly indicating a layer-by-layer growth mode. The origin of these oscillations is discussed in terms of existing models of growth mechanisms. Furthermore, it is emphasized that the so-called “pendulum” Kelvin probe is a very useful and inexpensive instrument for such in-situ film-growth investigations.

Relation between work and power calculated from force-velocity curves to that done during oscillatory work.

The force-velocity relation during oscillatory work was compared with that measured in the traditional way with quick release and force clamps using toad sartorius, frog sartorius, and mouse soleus muscles. Plotting the force and corresponding velocity data in this way produces a 'power-loop'. The 'power-loop' has less intuitive value than the frequently reported 'work-loops' but it is useful because it permits comparison with the force-velocity curve produced using traditional methods. The force/velocity combinations for oscillatory work during a contraction often exceed those that would be predicted from the force-velocity curve. Although it has been known for many years that more force is developed by stimulated muscle when it is being stretched than can be developed during an isometric contraction, my results show that the increase in force is of importance at stretch velocities that probably occur in vivo during locomotion.

Temperature and the energy cost of oscillatory work in teleost fast muscle fibres

Bundles of 20-30 fast muscle fibres were isolated from the abdominal myotomes of the short-horned sculpin (Myoxocephalus scorpius L.). The energy cost of contraction was measured during oscillatory work at 4 degrees C and 15 degrees C following treatment with iodoacetate and nitrogen gas to block glycolysis and aerobic metabolism. Isolated fibres were subjected to sinusoidal length changes about in situ resting length and stimulated at a selected phase in the strain cycle. Preliminary experiments with untreated preparations established the strain amplitude and stimulation parameters required to maximize work output over a range of cycle frequencies at 4 degrees C and 15 degrees C. Following oscillatory work, treated preparations were rapidly frozen, freeze-dried and the concentrations of phosphocreatine (PCr), creatine, adenosine 5'-triphosphate (ATP), adenosine 5'-di- and mono-phosphate and inosine 5-monophosphate measured by high performance liquid chromatography. The concentration of PCr declined in proportion to the total work done for up to 64 cycles without a significant change in ATP. Maximum power output was produced at a cycle frequency of 5 Hz at 4 degrees C (14-18 W/kg) and 17 Hz at 15 degrees C (23-27 W/kg). The rate of utilization of PCr per cycle was independent of temperature. However, since work per cycle was higher at 4 degrees C (2.7-3.7 mJ/g wet weight) than 15 degrees C (1.2-1.6 mJ/g wet weight), the energetic cost of contraction decreased with increasing temperature.

Energetics and Power Output of Isolated Fish Fast Muscle Fibres Performing Oscillatory Work

Fast myotomal muscle fibres were isolated from the cod (Gadus morhua L.) and the energy cost of contraction was measured under conditions simulating swimming. Fibre bundles were subjected to sinusoidal cycles of shortening and lengthening about their in situ fibre length, and stimulated at selected phases in each cycle. The preparations were poisoned with iodoacetic acid and bubbled with nitrogen to block the synthesis of ATP. After an initial rapid decline over the first 10 cycles, force and net work remained steady in some cases for up to 64 oscillatory length cycles, but more commonly declined slowly after about 30 cycles. The total mechanical work performed increased largely in proportion to the number of work cycles. At the end of each experiment fibres were frozen in isopentane cooled in liquid nitrogen and metabolite concentrations determined by high performance liquid chromatography (HPLC) and enzymatic analysis. Concentrations of adenylates did not differ significantly from control values, although a significant increase in IMP concentrations at 64 cycles accounted for the maintenance of relatively high energy charge values. Creatine (C) concentrations increased and creatine phosphate (CP) concentrations decreased, implying a tight coupling of the ATP/ADP reaction to the CP/C reaction. Muscle economy was calculated as the positive work performed during a work cycle divided by the total chemical energy expended. These values (approx. 7 mJ mumol-1) were found to be independent of the number of work cycles performed, although a trend to increase was observed. Muscle efficiency values, calculated assuming a Gibb's force free energy change for CP splitting in vivo of 55 kJ mol-1, were in the range 12-23%.

Power Output of Fish Muscle Fibres Performing Oscillatory Work: Effects of Acute and Seasonal Temperature Change

ABSTRACT Fast muscle fibres were isolated from the abdominal myotomes of the short-horned sculpin Myoxocephalus scorpius L. Sinusoidal length changes were imposed about resting muscle length and fibres were stimulated at a selected phase during the strain cycle. The work output per cycle was calculated from the area of the resulting force-position loops. The strain amplitude required for maximum work per cycle had a distinct optimum at ±5 % of resting length, which was independent of temperature. Maximum positive work loops were obtained by retarding the stimulus relative to the start of the length-change cycle by 30° (full cycle=360°). The maximum negative work output was obtained with a 210° stimulus phase shift. At intermediate stimulus phase shifts, work loops became complex with both positive (anticlockwise) and negative (clockwise) components. The number and timing of stimuli were adjusted, at constant strain amplitude (±5 % of resting muscle length), to optimize net positive work output over a range of cycle frequencies. The cycle frequency required for maximum power output (work per cycle times cycle frequency) increased from around 5-7 Hz at 4°C to 9-13 Hz at 15°C. The maximum tension generated per cycle at 15 °C was around two times higher at all cycle frequencies in summer-relative to winter-acclimatized fish. Fast muscle fibres from summer fish produced consistently higher tensions at 4°C, but the differences were only significant at 15 Hz. Acclimatization also modified the relationship between peak length and peak force at 4 °C and 15 °C. The maximum power output of muscle fibres showed little seasonal variation at 4°C and was in the range 20-25Wkg-1. In contrast, at 15°C, maximum muscle power output increased from 9 Wkg-1 in the winter-to 30 Wkg-1 in the summer-acclimatized fish.

Power Output and the Frequency of Oscillatory Work in Mammalian Diaphragm Muscle: the Effects of Animal Size

Bundles of muscle fibres were isolated from the diaphragm of mouse, rat and rabbit. Mean oscillatory power output was determined during phasic stimulation and imposed sinusoidal length changes. Maximum power output was measured over a range of cycle frequencies. The cycle frequency for maximum power output (fopt) decreased with increasing body mass and was described by the equation, fopt = 4.42M-0.16, where M is body mass. A very similar relationship has been reported between body mass and the frequency of the trot-gallop transition in terrestrial, quadrupedal mammals [Heglund et al. (1974), Science 186, 1112-1113), and the significance of this similarity is discussed.

Comparison of crossbridge dynamics between intact and skinned myocardium from ferret right ventricles.

This study compares the crossbridge kinetics of intact and skinned preparations from ferret cardiac muscles at 20 degrees C to determine whether skinning causes any alteration in the crossbridge response to an imposed length change. A papillary or trabecular muscle was isolated from the right ventricle, the muscle length adjusted to give the maximum twitch tension (Lmax), and the preparation was subjected to Ba2+ contracture. When steady tension developed, the length of the preparation was perturbed sinusoidally in 19 discrete frequencies, ranging from 0.13 to 135 Hz, and at a small peak-to-peak amplitude (0.25% Lmax). We identified three exponential processes in the sinusodial force-response to the imposed length oscillation, and these were labeled processes B, C, and D in order of increasing speed. A slow process, A, normally present in fast-twitch skeletal muscles, is very small or absent in cardiac muscles. Process B is an exponential delay, and the muscle produces oscillatory work on the forcing apparatus; processes C and D are exponential advances in which the muscle absorbs work. The preparation was chemically skinned and activated in the presence of (mM) CaEGTA 6 (pCa 4.55), MgATP 5, magnesium propionate 1, and phosphate 1, pH 7.0, with ionic strength adjusted to 200 mM with potassium propionate. We found that the crossbridge kinetics were not altered by the skinning procedure. The apparent rate constants extracted from the sinusoidal analysis were nearly identical in Ba2+ contracture (intact preparation) and in Ca2+ activation (skinned preparation), and the Nyquist plots were similar. Because the rate constants changed sensitively with the substrate (MgATP) concentrations, we concluded that the substrate is adequately supplied during Ba2+ contracture in the intact preparation. Our study demonstrates the compatibility of results obtained from an intact and from a skinned preparation.

Scaling Effects on Muscle Function: Power Output of Isolated Fish Muscle Fibres Performing Oscillatory Work

ABSTRACT Bundles of 3–10 live fast fibres were isolated from the abdominal myotomes of cod (Gadus morhua L.) 13–67 cm in length. The preparations performed work under conditions simulating their activity during swimming: sinusoidal length changes were imposed about in situ fibre length, and the fibres were stimulated at a selected phase in each cycle. Strain amplitude, and the number and timing of stimuli were chosen to give maximum power output over a wide range of cycle/tailbeat frequencies. For each preparation power output was maximal at a particular frequency, although the peaks were rather broad. As the size of the fish increased the cycle frequency for maximum power output (fopt) decreased, from 12.5 Hz (13 cm fish) to 5 Hz (67 cm fish) (fopt=1.67 L−0.52, where L is body length).

Covalent cross-linking of single fibers from rabbit psoas increases oscillatory power

Single fibers from chemically skinned rabbit psoas muscle were treated with 1-ethyl-3-[3-dimethyl-amino)proyl]-carbodiimide (EDC) at 20 degrees C after rigor was induced. A 22-min treatment resulted in 18% covalent cross-linking between myosin heads and the thin filament as determined by stiffness measurements. This treatment also results in covalent cross-linking among rod portions of myosin molecules in the backbone of the thick filament. The fibers thus prepared are stable and do not dissolve in solutions at ionic strengths as high as 1,000 mM. The preparation was subjected to sinusoidal analysis, and the resulting complex modulus data were analyzed in terms of three exponential processes, (A), (B), and (C). Oscillatory work (process B) was much greater in the cross-linked fibers than in untreated ones in activating solutions of physiological ionic strength (200 mM); this difference was attributed to the decline of process (A) with EDC treatment. Consequently, the Nyquist plot of the EDC-treated preparation exhibited an insect-type response. We conclude that, under these conditions, both cross-linked and non-cross-linked myosin heads contribute to the production of oscillatory power. The cross-linked preparations also exhibited oscillatory work in high ionic strength (500-1,000 mM) solutions, indicating that cross-linked myosin heads are capable of utilizing ATP to produce work. We conclude that process (A) does not relate to an elementary step in a cross-bridge cycle, but it may relate to dynamics outside the cross-bridge such as filament sliding or sarcomere rearrangement.

Changes in muscle stiffness produced by motor units of different types in peroneus longus muscle of cat

1. The effects of maximal tetanic contractions of varying numbers of motor units of the same type [slow (S), fast fatigue-resistant (FR), or fast fatigable (FF)] on the mechanical responses to muscle stretch were studied in the peroneus longus muscle of anesthetized cats. 2. Two types of stiffness measurements were made: 1) an average stiffness, defined as the tension change from the beginning to end of a 0.5-mm ramp stretch; and 2) a dynamic stiffness, defined as the ratio of peak-to-peak tension to amplitude of a maintained 85-microns sinusoidal stretch at frequencies of 10-80 Hz. 3. Contractions of slow and fast units elicited different increases in average stiffness. Type S units, although developing much smaller tetanic tensions than fast ones, produced a resistance to stretch comparable with or greater than that of fast units developing much higher tensions. 4. For comparable tetanic tensions, slow units also elicited a greater dynamic stiffness than fast units. During sinusoidal stretch, changes in muscle tension led changes in muscle length during contraction of S units, but the reverse was observed for frequencies 30-50 Hz during contraction of FF units. This suggests that the latter perform oscillatory work on the driving apparatus. 5. Type S units, whose low-threshold motoneurons are the first to be recruited, appear well adapted to play a role in posture and in slow movements because of the resistance they offer to forces tending to change joint position or to oppose the progression of slow movements.

Changes in the ATPase activity of insect fibrillar flight muscle during sinusoidal length oscillation probed by phosphate-water oxygen exchange.

Extensive phosphate-water oxygen exchange occurs when ATP is hydrolyzed in an [18O]water medium by length oscillated and Ca2+-activated, chemically skinned fibers from the flight muscle of the giant waterbug Lethocerus indicus. For fibers which are length oscillated under conditions not optimal for ATPase activity or oscillatory work, the pattern of exchange shows two pathways for hydrolysis. One pathway has low exchange, because steps controlling Pi release are rapid; the other pathway has high exchange and slow Pi release. Steps controlling Pi release appear rate-limiting for changes in the high-exchange ATPase activity that occur on varying the frequency and amplitude of oscillation. On length oscillation under conditions of optimal ATPase activity or work, only the high-exchange pathway is present. Cross-bridges following the high-exchange pathway are therefore responsible for oscillatory work, the physiological function of the muscle, and behave uniformly with respect to oxygen exchange. The single pathway and the magnitude of the ATPase activity are both similar to results with isometric strained fibers (Lund, J., Webb, M. R., and White, D. C. S. (1987) J. Biol. Chem. 262, 8584-8590). A qualitative model is suggested for oscillatory work by cross-bridges, arising from the common periodicity of the thick and thin filaments in insect flight muscle.

The Acute Effects of Pneumonectomy on Pulmonary Vascular Impedance in the Dog

Pulmonary vascular impedance is a measure of the pulsatile characteristic of pressure and flow that occurs in the proximal pulmonary arteries. Pulmonary vascular resistance (PVR) is most influenced by the distal circulation of the lung. This study was performed to evaluate the changes that occurred in pulmonary vascular impedance, as well as in other hemodynamic variables, following pneumonectomy by a closed-chest method in 10 anesthetized dogs. The following observations were made (numbers compare mean values for the 10 dogs before and after pneumonectomy): (1) PVR increased from 447 to 761 dyne sec cm −5 ( p = .02); (2) the oscillatory work of the right ventricle increased from 1.23 to 1.76 J/min ( p = .006); (3) the mean pulmonary artery pressure increased from 14 to 18.8 mm Hg ( p = .0001); and (4) cardiac output and heart rate remained unchanged. Surprisingly, the estimated characteristic impedance (the impedance to oscillatory flow in the proximal bed) did not change significantly (279 to 296 dyne sec cm −5). This observation cannot be explained by the usual lumped compartmental models classically used to characterize the pulmonary vascular bed.

The ATPase kinetics of insect fibrillar flight muscle myosin subfragment-1.

Myosin subfragment-1 (S1) has been prepared from the fibrillar flight muscles of the giant water bug Lethocerus by chymotryptic digestion of myofibrillar suspensions in the absence of magnesium ions. The S1 obtained has a single light chain and a heavy chain with molecular weights of about 18 kDa and 90 kDa respectively. The kinetics of the elementary steps of the magnesium-dependent ATPase of insect S1 and rabbit S1 are similar, both with ATP and with ATP analogues as substrates. However, the presence of variable amounts of inactive protein within our preparation means that several rate constants cannot be obtained with as much precision in the case of insect S1. The most striking differences between the rabbit and insect S1 are values for the Vmax and the Km of actin during actin-activation of the MgATPase activity, which are up to an order of magnitude lower and greater in the insect than in the rabbit, respectively. The mechanical properties of strain activation and of capacity to do extended oscillatory work are unique to insect fibrillar flight muscle and distinguish it from vertebrate striated muscle. It is likely that these properties reflect differences in the organization of actin and myosin within the respective filament lattices rather than intrinsic differences in the ATPase mechanisms of the isolated myosin molecules from the two types of muscle.

Crossbridge kinetics in chemically skinned rabbit psoas fibres when th actin-myosin lattice spacing is altered by dextran T-500

The actin-myosin lattice spacing of chemically skinned rabbit psoas fibres was osmotically altered by dextran T500, and the transient kinetic response of tension arising from maximally cycling cross-bridges was measured by sinusoidal length perturbations. The lattice spacing was estimated from the width of the fibres measured under a light microscope. As the dextran concentration was increased, the widths during both relaxation and Ca-activation decreased monotonically. The tension increased to a maximum at 7% dextran, and decreased again at further increases in dextran. Dynamic modulus (stiffness) increased monotonically with compression by dextran; this increase is primarily due to the elastic modulus. The rate constants slightly decreased between 0% and 4% dextran, then decreased rapidly at higher concentrations. The rate of oscillatory work output stayed approximately constant between 0% and 4% dextran, and sharply decreased at higher concentrations. Apparently, two independent effects occur as the lattice is compressed by dextran: (1) a compensation for the spacing change through an increase in tension and a decrease in the rate constants (this takes place at low dextran concentrations); and (2) an alteration of the crossbridge kinetics by grossly decreasing both the tension and the rate constants (at high dextran concentrations). The first effect is interpreted as a decrease in the detachment rate, while the second effect is interpreted as a decrease in the rate of the 'power stroke' reaction.

A possible mechanism of length activation in insect fibrillar flight muscle.

When insect fibrillar flight muscle is stretched it becomes more active, as indicated by an increase in oscillatory work output and ATPase activity. Using glycerol-extracted muscle it is demonstrated that this effect is periodic with a repeat of around 3% length change, independent of temperature and ionic strength. This corresponds to 38 nm per half sarcomere, the same repeat as the actin helix. Since there is also a period of 38 nm in the myosin helix the periodic change of activity with muscle length could be caused by filament sliding. This may be the basis of the mechanism of length activation.