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N A Curtin

Publications and source records attributed to N A Curtin.

At least 19 recordsLinked to original sources
PubMed2005

Influence of ionic strength on the time course of force development and phosphate release by dogfish muscle fibres.

We measured the effects of ionic strength (IS), 200 (standard) and 400 mmol l(-1) (high), on force and ATP hydrolysis during isometric contractions of permeabilized white fibres from dogfish myotomal muscle at their physiological temperature, 12 degrees C. One goal was to test the validity of our kinetic scheme that accounts for energy release, work production and ATP hydrolysis. Fibres were activated by flash photolysis of the P(3)-1-(2 nitrophenyl) ethyl ester of ATP (NPE-caged ATP), and time-resolved phosphate (P(i)) release was detected with the fluorescent protein MDCC-PBP, N-(2[1-maleimidyl]ethyl)-7-diethylamino-coumarin-3-carboxamide phosphate binding protein. High IS slowed the transition from rest to contraction, but as the fibres approached the isometric force plateau they showed little IS sensitivity. By 0.5 s of contraction, the force and the rate of P(i) release at standard and high IS values were not significantly different. A five-step reaction mechanism was used to account for the observed time courses of force and P(i) release in all conditions explored here. Only the rate constants for reactions of ATP, ADP and P(i) with the contractile proteins varied with IS, thus suggesting that the actin-myosin interactions are largely non-ionic. Our reaction scheme also fits previous results for intact fibres.

Actomyosin↗
PubMed2003

Actomyosin energy turnover declines while force remains constant during isometric muscle contraction.

Energy turnover was measured during isometric contractions of intact and Triton-permeabilized white fibres from dogfish (Scyliorhinus canicula) at 12 degrees C. Heat + work from actomyosin in intact fibres was determined from the dependence of heat + work output on filament overlap. Inorganic phosphate (Pi) release by permeabilized fibres was recorded using the fluorescent protein MDCC-PBP, N-(2-[1-maleimidyl]ethyl)-7-diethylamino-coumarin-3 carboxamide phosphate binding protein. The steady-state ADP release rate was measured using a linked enzyme assay. The rates decreased five-fold during contraction in both intact and permeabilized fibres. In intact fibres the rate of heat + work output by actomyosin decreased from 134 +/-s.e.m. 28 microW mg(-1) (n = 17) at 0.055 s to 42% of this value at 0.25 s, and to 20% at 3.5 s. The force remained constant between 0.25 and 3.5 s. Similarly in permeabilized fibres the Pi release rate decreased from 5.00 +/- 0.39 mmol l(-1) s(-1) at 0.055 s to 39% of this value at 0.25 s and to 19% at 0.5 s. The steady-state ADP release rate at 15 s was 21% of the Pi rate at 0.055 s. Using a single set of rate constants, the time courses of force, heat + work and Pi release were described by an actomyosin model that took account of the transition from the initial state (rest or rigor) to the contracting state, shortening and the consequent work against series elasticity, and reaction heats. The model suggests that increasing Pi concentration slows the cycle in intact fibres, and that changes in ATP and ADP slow the cycle in permeabilized fibres.

Actomyosin↗
PubMed2003

Energy storage during stretch of active single fibres from frog skeletal muscle.

Heat production and force were measured during tetani of single muscle fibres from anterior tibialis of frog. During stimulation fibres were either kept under isometric conditions, or were stretched or allowed to shorten (at constant velocity) after isometric force had reached its plateau value. The energy change was evaluated as the sum of heat and work (work = integral of force with respect to length change). Net energy absorption occurred during stretch at velocities greater than about 0.35 L0 s-1 (L0 is fibre length at resting sarcomere length 2.10 microm). Heat produced by 1 mm segments of the fibre was measured simultaneously and separately; energy absorption is not an artefact due to patchy heat production. The maximum energy absorption, 0.092 +/- 0.002 P0L0 (mean +/- S.E.M., n = 8; where P0 is isometric force at L0), occurred during the fastest stretches (1.64 L0 s-1) and amounted to more than half of the work done on the fibre. Energy absorption occurred in two phases. The amount in the first phase, 0.027 +/- 0.003 P0L0 (n = 32), was independent of velocity beyond 0.18 L0 s-1. The quantity absorbed in the second phase increased with velocity and did not reach a limiting value in the range of velocities used. After stretch, energy was produced in excess of the isometric rate, probably from dissipation of the stored energy. About 34 % (0.031 P0L0/0.092 P0L0) of the maximum absorbed energy could be stored elastically (in crossbridges, tendons, thick, thin and titin filaments) and by redistribution of crossbridge states. The remaining energy could have been stored in stretching transverse, elastic connections between myofibrils.

Adenosine Triphosphate↗
PubMed2002

Excess recovery heat production by isolated muscles from mice overexpressing uncoupling protein-3.

Contractile and energetic performance of bundles of muscle fibres from the soleus of mice overexpressing uncoupling protein 3 (UCP-3tg) were compared with the performance of bundles from wild-type mice. Force and heat production were measured during a series of thirty 0.2 s isometric tetani at L(o), the length optimal for force. UCP-3tg fibres were as strong as the wild-type and maintained force in the series equally well; in the first tetanus force was 116.9 +/- 15.1 and 133.3 +/- 19.7 mN x mm(-2) respectively (all values means +/- S.E.M., n = 6 for UCP-3tg and n = 5 for wild-type). Heat production was partitioned into initial heat (due to contractile ATPases and the creatine kinase reaction) and recovery heat (due to other ATP-supplying processes) and expressed relative to the first cycle total heat. Initial heat production was similar for the UCP-3tg and wild-type fibres, decreasing during the series from 0.799 +/- 0.052 to 0.661 +/- 0.061 relative units (UCP-3tg), and from 0.806 +/- 0.024 to 0.729 +/- 0.039 relative units (wild-type). In both types the recovery heat was small at the start of the series and increased as the series progressed. At the end of the series, recovery heat production by UCP-3tg fibres, 1.575 +/- 0.246 relative units, was twice that of the wild-type fibres, 0.729 +/- 0.072 relative units. The extra recovery heat represents inefficient recovery in UCP-3tg fibres. This is the first direct evidence of enhanced energy dissipation as heat when UCP-3tg is overexpressed.

Adenosine Triphosphate↗
PubMed2002

Isometric and isovelocity contractile performance of red muscle fibres from the dogfish Scyliorhinus canicula.

Maximum isometric tetanic force produced by bundles of red muscle fibres from dogfish, Scyliorhinus canicula (L.), was 142.4+/-10.3 kN m(-2) (N=35 fibre bundles); this was significantly less than that produced by white fibres 289.2+/-8.4 kN m(-2) (N=25 fibre bundles) (means +/- S.E.M.). Part, but not all, of the difference is due to mitochondrial content. The maximum unloaded shortening velocity, 1.693+/-0.108 L(0) s(-1) (N=6 fibre bundles), was measured by the slack-test method. L(0) is the length giving maximum isometric force. The force/velocity relationship was investigated using a step-and-ramp protocol in seven red fibre bundles. The following equation was fitted to the data: [(P/P(0))+(a/P(0))](V+b)=[(P(0)(*)/P(0))+(a/P(0))]b, where P is force during shortening at velocity V, P(0) is the isometric force before shortening, and a, b and P(0)(*) are fitted constants. The fitted values were P(0)(*)/P(0)=1.228+/-0.053, V(max)=1.814+/-0.071 L(0) s(-1), a/P(0)=0.269+/-0.024 and b=0.404+/-0.041 L(0) s(-1) (N=7 for all values). The maximum power was 0.107+/-0.005P(0)V(max) and was produced during shortening at 0.297+/-0.012V(max). Compared with white fibres from dogfish, the red fibres have a lower P(0) (49%) and V(max) (48%), but the shapes of the force/velocity curves are similar. Thus, the white and red fibres have equal capacities to produce power within the limits set by the isometric force and maximum velocity of shortening of each fibre type. A step shortening of 0.050+/-0.003L(0) (N=7) reduced the maximum isometric force in the red fibres' series elasticity to zero. The series elasticity includes all elastic structures acting in series with the attached cross-bridges. Three red fibre bundles were stretched at a constant velocity, and force (measured when length reached L(0)) was 1.519+/-0.032P(0). In the range of velocities used here, -0.28 to -0.63V(max), force varied little with the velocity.

Animals↗
PubMed2001

Synchronous oscillations of length and stiffness during loaded shortening of frog muscle fibres.

1. A study was made of the damped oscillations in fibre length that are observed when isolated muscle fibres from the frog are released during the plateau of an isometric tetanus to shorten against a constant load (force clamp recording) near the isometric level (temperature, 1.0-11.0 degrees C; initial sarcomere length, 2.25 microm). 2. The oscillatory length changes of the whole fibre were associated with similar length changes of marked consecutive segments along the fibre. The segmental length changes were initially in synchrony with the whole-fibre movements but became gradually more disordered. At the same time the length oscillation of the whole fibre was progressively damped. 3. The fast length step that normally occurs at the outset of the load-clamp manoeuvre was essential for initiating the oscillatory behaviour. Accordingly, no length oscillation occurred when the load clamp was arranged to start as soon as the selected tension level was reached during the rising phase of the tetanus. 4. The instantaneous stiffness was measured as the change in force that occurred in response to a high-frequency (2-4 kHz) length oscillation of the fibre. During the load-clamp manoeuvre, when the tension was kept constant, the stiffness underwent periodic changes that correlated well in time with the damped oscillatory changes in fibre length. However, there was a phase shift between the stiffness oscillation and the oscillation of shortening velocity, the latter being in the lead of the stiffness response by 21.4 +/- 0.8 ms (n = 19) at 1.8 +/- 0.1 degrees C. 5. A mechanism is proposed to explain the oscillatory behaviour of the muscle fibre based on the idea that the quick length step at the outset of the load clamp leads to synchronous activity of the myosin cross-bridges along the length of the fibre.

Acids↗
PubMed2001

Mechanical properties of red and white swimming muscles as a function of the position along the body of the eel Anguilla anguilla.

The way in which muscles power steady swimming depends on a number of factors, including fibre type and recruitment, muscle strain, stimulation pattern and intensity, and the intrinsic mechanical properties of the muscle fibres. For a number of undulatory swimming fish species, in vivo studies have shown that muscles at different positions along the body are stimulated during different phases of the strain cycle. Moreover, some intrinsic contractile properties of the muscles have been found to vary according to their position along the body. We report the first results on the mechanical properties of the red and white muscles of an anguilliform swimmer, Anguilla anguilla. Small preparations (0.147-1.335 mg dry mass) were dissected from positions at fractions of 0.2, 0.4, 0.6 and 0.8 of total body length (BL). We determined the time to 50% and 100% peak force and from the last stimulus to 50% relaxation for isometric contractions; we measured the sarcomere lengths that coincided with in situ resting length. None of these quantities varied significantly with the longitudinal position from which the fibres were taken. We also measured power and work output during contractions under conditions approximating those used in vivo (cycle frequency, 1Hz; strain amplitude, +/- 10%L(0), where L(0) is the length giving maximum isometric force). During these experiments, work output was affected by stimulation phase, but did not depend on the longitudinal position in the body from which the muscles were taken. Our results indicate that red and white eel muscles have uniform properties along the body. In this respect, they differ from the muscle of most non-anguilliforms, in which muscle kinetics varies in a systematic way along the body. Uniform properties may be beneficial for anguilliform swimmers, in which the amplitude of the travelling wave can be pronounced over the entire body length.

Anguilla↗
PubMed2000

Energy storage by passive elastic structures in the mantle of sepia officinalis.

The passive elastic properties of the mantle of the cuttlefish Sepia officinalis have been characterized in experiments on intact mantle and on pieces cut from the mantle. The mantle was found to be very compliant over a wide range of circumferential strains, corresponding to a change in mantle circumferential strain of 0.45. Beyond this range of strain, the mantle was much stiffer, in both the circumferential direction, 0.542+/-0.025 MPa (mean +/- s.e.m., N=51) and through the thickness of the mantle wall, 0.152+/-0.041 MPa (N=11). Almost 80 % of the work done on the tissue during compression in the circumferential direction was recovered during elastic recoil of the tissue; this elastic work could contribute to refilling the mantle after a jet. Our estimates of the work done during a cycle of jetting and refilling show that such elastic work is small (approximately 1 %) compared with the contractile work done by the circular muscle fibres. However, although the elastic work is almost negligible in the overall energy budget, it is probably sufficient to power refilling of the mantle.

Animals↗
PubMed2000

Heat production and oxygen consumption during metabolic recovery of white muscle fibres from the dogfish Scyliorhinus canicula.

Oxygen consumption and heat production were measured during contraction and recovery of isolated, white muscle fibres from dogfish (Scyliorhinus canicula) at 19 degrees C. The contraction period consisted of 20 isometric twitches at 3 Hz; this was followed by a recovery period of 2 h without stimulation. We tested the hypothesis that recovery is wholly oxidative (not glycolytic) in these fibres. The following features support this hypothesis. (i) The ratio of total heat produced to oxygen consumed, 451+/-34 kJ mol(-)(1) (mean +/- s.e.m., N=29), was close to that expected for either the oxidation of carbohydrate, 473 kJ mol(-)(1), or the oxidation of fat, 439 kJ mol(-)(1). Even assuming the maximum value (95 % confidence limit) of the observed heat production, glycolysis could account for resynthesis of at most 18 % of the ATP used during the contractions. (ii) When the difference in rates of diffusion of oxygen and heat within the muscle are taken into account, the time courses of oxygen consumption and heat production match each other well during the entire recovery period. The efficiency of recovery (=energy used for ATP synthesis/energy available for ATP synthesis) was estimated from the results. This value, 84.0+/-20.1 % (mean +/- s.e.m., N=29), is relatively high and represents the first such measurement in functioning muscle.

Animals↗
PubMed1998

Contraction with shortening during stimulation or during relaxation: how do the energetic costs compare?

White muscle fibres from dogfish were used to compare the energetic costs of shortening by fully active muscle and by relaxing muscle. The muscle preparation was tetanized for 0.6 s and shortened either during stimulation or during relaxation. The distance shortened was 1 mm (about 15% L0, the muscle length optimum for force) and the velocity was 3.5 or 7.0 mm s-1 (about 15 or 30% V0, the maximum velocity of shortening). Isometric tetani at L0 were also investigated. Mechanical work and heat production were measured, and work + heat was taken as a measure of energetic cost. Both work and the energetic cost were higher with shortening during stimulation than with shortening during relaxation. The results suggest that shortening during relaxation, which is known to occur during locomotion in vivo, may be an energy-saving strategy.

Adenosine Triphosphatases↗
PubMed1998

Predictions of the time course of force and power output by dogfish white muscle fibres during brief tetani.

The aim of this study was to identify the principal factors that determine the time course of force and power output by muscle during patterns of stimulation and movement similar to those during fish swimming. Fully activated, white muscle fibres isolated from dogfish Scyliorhinus canicula were used to characterize the force-velocity relationship of the contractile component (CC) and the stress-strain relationship of the passive, elastic component (SEC) in series with the CC. A simple model of the time course of crossbridge activation during brief contractions was devised. Using the mechanical properties of the CC and SEC and the activation time course, force and power were predicted for brief contractions with constant-velocity movement and also for brief contractions starting at various times during sinusoidal movement. The predicted force and power were compared with observations for these patterns of stimulation and movement. The predictions matched the observations well for the period during stimulation. Matching of force was much less good for some specific conditions during relaxation, the period during which force persists after the end of stimulation. If either the slow rise of activation or the SEC was omitted from the calculation, the predictions were poor, even during stimulation. Additional factors which may influence force are discussed. These include the after-effects of shortening and stretch, the variation of force during constant-velocity stretch and non-uniform behaviour within the muscle.

Animals↗
PubMed1998

Distinguishing metabolic heat from condensation heat during muscle recovery.

When a thermopile is used to measure the heat production of isolated muscle, the muscle is surrounded by gas saturated with water vapour, initially in equilibrium with the muscle. After contraction, the osmolarity of the muscle is raised so that it is no longer in equilibrium with the gas around it, and condensation will occur. When artificial muscles of known osmolarity were placed on a thermopile surrounded by gas in equilibrium with a solution of lower osmolarity, their temperature was found to be raised (by 102.7 mK osmol-1 l). This temperature increase was greatly reduced by covering the artificial muscle with a Teflon film. Experiments on living muscle from the dogfish Scyliorhinus canicula showed that muscle temperature was higher 2 min after a series of 20 twitches at 3 Hz if the muscle was not covered by Teflon than if it was covered. The Teflon covering did not diminish the muscle's contractile performance. We conclude that the condensation of water does contribute to the heat measured during the recovery period, but that when the muscle is covered by Teflon film condensation heat can largely be prevented so that only genuine metabolic recovery heat is produced.

Animals↗
PubMed1998

Shortening during stimulation vs. during relaxation. How do the costs compare?

White muscle fibres from dogfish were used to investigate the energetic cost of shortening by fully active muscle and by relaxing muscle. The muscle preparation was tetanized for 0.6 s and shortened by 1 mm (about 15% L0) at 7 mm/s (about 30% V0) either during stimulation or during relaxation. Isometric tetani at L0 were also investigated. Mechanical work was calculated from force and length change. Work + heat was taken as a measure of energetic cost. Both work and energetic cost were higher for shortening during stimulation than during relaxation. We also evaluated separately the work and heat associated with the contractile component and with the series elastic component. Work stored in the series elasticity could be completely recovered as external work when the shortening occurred during relaxation.

Animals↗
PubMed1997

Recovery after contraction of white muscle fibres from the dogfish Scyliorhinus canicula.

Recovery after contraction of white muscle fibres of dogfish was investigated using 31P-NMR and measurements of heat production. The muscle fibres were stimulated to perform either a single isometric tetanus or a series of brief isometric tetani; the NMR measurements showed that approximately half of the phosphocreatine (PCr) was used. The period of activity was followed by a recovery period without stimulation. Both NMR and heat measurements agreed in showing that recovery was very slow, requiring at least 60 min for PCr resynthesis and for the production of recovery heat. The NMR results showed that changes in intracellular pH and in the concentrations of PCr and intracellular phosphate (Pi) had very similar time courses. Intracellular pH moved in the alkaline direction during the period of activity and then returned monotonically during recovery. The non-phosphate buffer power was 13.0 +/- 3.1 mmol l-1 intracellular water per pH unit (N = 4, mean +/- S.E.M.). The results are consistent with the view that oxidative processes resynthesize PCr during recovery, which is slow because of the low mitochondrial content of these muscle fibres.

Animals↗
PubMed1995

Effects of alpha-cyano-4-hydroxycinnamic acid on fatigue and recovery of isolated mouse muscle.

Fatigue and recovery of mouse soleus and extensor digitorum longus muscles were investigated in standard saline and in saline containing the lactate + hydrogen ion transport blocker, alpha-cyano-4-hydroxycinnamic acid (cinnamate). The fatigue protocol was a series of brief isometric tetani which reduced isometric force by about 25%. Recovery was monitored by test tetani during recovery. Both muscles recovered completely in standard saline. Soleus muscle also recovered completely in the presence of cinnamate, whereas extensor digitorum longus hardly recovered at all. Force during fatigue and recovery can be described in a mathematical simulation in which force depends on intracellular inorganic phosphate and pH, and the only effect of cinnamate is to block lactate + hydrogen ion transport. The results of the simulation suggest that during the fatiguing series of tetani pH changes are small and have a negligible effect on force, but pH is a major determinant of the timecourse of recovery in extensor digitorum longus.

Animals↗