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R C Woledge

Publications and source records attributed to R C Woledge.

At least 55 records · Page 3Linked to original sources
PubMed1991

In mice, the muscle weakness due to age is absent during stretching.

1. The contractile force was compared in isolated soleus muscles from young (2.5-8 months old) and aged (28-31 months old) mice. Force was measured at 25 degrees C during isometric tetanic contractions during isovelocity stretching and shortening contractions. 2. The normalized isometric force was lower by 13.3% in muscles from aged mice. Muscles from young and aged mice produced 0.951 +/- 0.031 N mg-1 (n = 12) and 0.824 +/- 0.048 N mg-1 (n = 9) respectively. The relaxation time, from 90 to 10% of the tetanic force, of muscles from aged mice was 102.1 +/- 3.7 ms (n = 6), which was longer than that for muscles from young mice, 84.4 +/- 3.8 ms (n = 6) (means +/- S.E.M.). 3. The force during shortening was also reduced in muscles from aged animals by the same proportion as the isometric force. Therefore the force during shortening relative to the isometric force was the same in muscles from young and aged mice. 4. During rapid stretching soleus muscles from aged mice produced a similar force to those from young mice. Therefore stretch can remove the weakness in muscles of aged mice. 5. These changes in muscles from aged mice are similar to those produced when inorganic phosphate (Pi) levels are raised, in skinned rabbit psoas fibres, or during fatigue or with low intracellular pH (pHi), in frog muscle. It is possible therefore that the force loss due to ageing may be due to a higher Pi level or a lower pHi.

Aging↗
PubMed1991

Efficiency of energy conversion during shortening of muscle fibres from the dogfish Scyliorhinus canicula.

Force and heat production were measured during isovelocity shortening of tetanized white myotomal muscle fibres from the dogfish at 12 degrees C. For each fibre preparation a range of velocities was used. Mechanical power was calculated from force X velocity of shortening. The rate of total energy output during shortening was evaluated as the sum of mechanical power and the rate of heat production. The ratio of mechanical power to total energy rate was taken as a measure of efficiency of energy conversion to mechanical power during shortening. Efficiency was maximal and varied little in the range of shortening velocities 0.42-0.89 fibres lengths s-1 (0.11-0.23 Vmax); maximal efficiency was 0.33 +/- 0.01 (+/- S.E.M., N = 23 measurements on seven fibre bundles). The efficiency of the white fibres from dogfish was less than that measured in the same way in earlier experiments on frog muscle and tortoise muscle.

Animals↗
PubMed1990

Analysis of thermopile records from contracting isolated cardiac muscle.

Recovery heat production after contraction in rabbit papillary muscle at 20 degrees C occurs at an exponentially declining rate. The time constant describing this decline is 25 s; it is not different when 10 twitches or when a steady-state twitch train is studied, and it is unaltered by changing stimulus frequency from 0.125 to 0.2 Hz. The same value has previously been found after single twitches. If it is assumed that phosphocreatine (PCr) resynthesis is the cause of recovery heat production and that it occurs also during contractions at a rate proportional to the amount of PCr depletion, it is possible to divide the total heat production for any period of stimulation into that caused by this recovery process (R) and that caused by initial (I) processes (presumed to be PCr splitting). The value of R/I obtained by using this method is 1.10 +/- 0.04 (means +/- SE, n = 27 muscles), close to the theoretical value of 1.13. The correspondence between the measured and the predicted ratio supports the assumptions underlying the measurement. Thus in heart muscle the heat produced during and after contraction can be explained by PCr splitting and reformation. The older Bugnard method of analysis applied to the same data gives an R/I value of 1.5; the reasons for the discrepancy are described.

Animals↗
PubMed1990

Influence of temperature on mechanics and energetics of muscle contraction.

Results gleaned from use of temperature as a probe to study skeletal muscle performance and mechanisms of activation and contraction are reviewed. Steady-state and non-steady-state responses to changes in temperature are considered. Temperature sensitivities, Q10 values, of mechanical and energetic parameters range from nearly 1 to greater than 5 in frog skeletal muscle. Factors that are less temperature sensitive (Q10 less than or equal to 1.5) are peak tetanic force, instantaneous stiffness, curvature of force-velocity relation, magnitude of labile heat, and mechanical efficiency. Rates with intermediate temperature sensitivities (Q10 greater than 2 but less than 3) include rate of isometric force development, maximum shortening velocity, and relaxation from a brief tetanus. Rates with high temperature sensitivities (Q10 greater than 3) include cross-bridge turnover during an isometric tetanus, isometric economy, maximum power output, Ca2+ sequestration by sarcoplasmic reticulum, relaxation from a prolonged tetanus, and recovery metabolism. The observation that the Q10 for relaxation rate depends on tetanic duration can be explained in terms of the possible role of parvalbumin as a soluble relaxing factor.

Animals↗
PubMed1989

Effect of subnutrition on normalized muscle force and relaxation rate in human subjects using voluntary contractions.

1. Muscle weakness and wasting are well-known consequences of subnutrition, but there have been no published comparisons of these variables in a single muscle or muscle group. We report voluntary force measurements of adductor pollicis muscle in 11 subnourished patients normalized for their cross-sectional areas. We also report normalized relaxation rates of these contractions and the results are compared with those obtained in 40 healthy normally nourished subjects. 2. Normalized muscle force was no different in the subnourished group. However, relaxation rate was significantly slower than in the control group.

Adult↗
PubMed1989

Effect of age on voluntary force and cross-sectional area of human adductor pollicis muscle.

Muscle weakness accompanies ageing but its causes are still uncertain. We report maximum voluntary force measurements of adductor pollicis muscle, normalized for cross-sectional area, in twenty-three elderly subjects. Normalized force was lower in the elderly compared with a group of fifty-five young adult subjects by 27 +/- 4% (S.E.M.). This shows that atrophy alone is not the cause of the weakness of old age.

Adult↗
PubMed1989

Variation in the normalized tetanic force of single frog muscle fibres.

1. The forces produced in maximal fixed-end tetani of single fibres isolated from the anterior tibialis muscle of the frog Rana temporaria have been measured at sarcomere lengths of 2.2 microns and temperatures near 0 and 10 degrees C. 2. When normalized by either cross-sectional area or dry weight per unit length at a sarcomere length of 2.2 microns, the forces vary over a twofold range. 3. The normalized force is not significantly correlated with the velocity of unloaded shortening or the twitch characteristics of the fibres. Lack of variability of these two quantities (together with histochemical evidence) suggest that only one fibre type is present in the experimental sample. 4. The steady rate of energy liberation (stable, heart rate) of the fibres during isometric tetani is positively correlated with the normalized force, indicating that extra ATP splitting is required to produce higher forces. 5. Fibres with a higher ratio of dry weight per unit length to cross-sectional area ('dry density') show a higher force when normalized by area, but not when normalized by dry weight per unit length. 6. Fibres with a more circular cross-sectional profile produce more force when normalized by either cross-sectional area or dry weight per unit length. The significance of this correlation is unclear. 7. The contribution of various sources to the total overall variation in normalized force is assessed. It is suggested that a diffusible substance or substances may be involved in modulating fibre force.

Adenosine Triphosphatases↗
PubMed1988

Molar enthalpy change for hydrolysis of phosphorylcreatine under conditions in muscle cells.

The enthalpy change for the hydrolysis of phosphorylcreatine (PCr) by hydrochloric acid or by alkaline phosphatase was observed at 0, 25, and 37 degrees C. The value for delta H is -44 kJ mol-1 under alkaline, Mg2+-free conditions and is almost independent of temperature, ionic strength, and concentration of reactants. In muscle the reaction is accompanied by a transfer of protons from the buffers (largely histidine) to orthophosphate, release of Mg2+ from PCr, and binding of Mg2+ to orthophosphate. Measurements are reported of the heats of these processes. The calculated value of the overall heat of hydrolysis of PCr (including these processes) at pH 7, pMg 3 is -35 kJ mol-1.

Calorimetry↗
PubMed1988

Effect of intracellular pH on force and heat production in isometric contraction of frog muscle fibres.

1. The intracellular pH (pHi) of live fibres from the anterior tibialis of the frog Rana temporaria was measured at 10 degrees C (using pH-sensitive microelectrodes) in Ringer solutions containing a fixed bicarbonate concentration (20 mM) and varying PCO2 concentrations of 0.5-54%. As extracellular pH was changed from 7.99 to 6.00, mean pHi changed from 7.24 to 5.97. Similar results were obtained at 20 degrees C. 2. In parallel experiments force and rate of heat production in 4 s isometric tetani at 10 degrees C were measured, and compared to control observations (5% CO2, pHi 6.80). 3. As the fibres became more acid (to pHi 5.95), force and heat rate were progressively reduced (to 0.75 and 0.71 of the control values, respectively). 4. As the fibres became more alkaline (to pHi 7.26), force increased slightly (by a maximum of 0.03 of the control value) but heat rate did not increase. 5. When the dependence on pH of the molar enthalpy change for phosphocreatine splitting is taken into account, these results indicate that the force-time integral per cross-bridge cycle increases with pHi over this range.

Animals↗
PubMed1988

The energetics of work and heat production by single muscle fibres from the frog.

During active shortening the heat rate in isolated muscle fibres is greater than during isometric contraction, and increases with velocity of shortening (V), but at a decreasing rate as the maximum velocity (V0) is approached. For shortening at V less than 0.25 V0 the amount of extra heat produced during a period of shortening is proportional to the distance shortened, but for rapid shortening (V greater than 0.5 V0) the extra heat increases less than proportionally with the distance shortened. After a period of shortening the higher heat rate returns to the isometric level over a period of several hundred milliseconds. A similar period of increased heat rate is seen after a quick release. After shortening 10% of muscles slack length at 0.1 V0 the amount of heat produced during tension redevelopment is similar to that after a quick release. But after more rapid shortening there is less heat production than after a quick release.

Adenosine Triphosphate↗
PubMed1986

Absolute values of myothermic measurements on single muscle fibres from frog.

The heat and force produced in tetanic contraction of single fibres from anterior tibialis muscle of the frog Rana temporaria have been observed at measured temperatures close to 1 and 10 degrees C. Heat was measured using a Hill-Downing type thermopile. In control experiments with a resistor of known heat capacity comparable to a single muscle fibre, it was found that Peltier and Joule heating produced identical thermopile outputs. The Peltier method was used to introduce a known amount of heat into the system in each experiment with a muscle fibre. From the response to this heating the heat capacity of each preparation was obtained and used to calculate the absolute amount of heat production from the thermopile output. The heat produced during tetanic contraction (H) could be described by Aubert's equation [H = Ha (1 - e-t/tau) + hbt]. In some fibres there was no labile heat (Ha), whereas in others it was clearly present. The stable heat rate (hb) was strongly temperature dependent (Q10 = 4.06). At 0 degree C the stable heat rate (normalized by dry weight) in the single fibres was significantly greater than that in whole anterior tibialis muscle.

Animals↗
PubMed1986

Labile heat and changes in rate of relaxation of frog muscles.

Observations were made of the labile heat and the progressive slowing of relaxation as a function of tetanus duration (Abbott effect) during isometric tetani of frog extensor longus digiti IV (e.l.d. iv) and sartorius muscle. Both the labile heat and slowing of relaxation are less marked in e.l.d. iv than in sartorius muscle. Both effects are depressed to the same extent in the second of two closely spaced tetani in sartorius muscle. The repriming of both effects follows the same time course in sartorius muscle. The hypothesis is discussed that both effects result from binding of calcium to parvalbumin during a tetanus, and that their repriming is due to the removal of calcium from parvalbumin by the sarcoplasmic reticulum.

Animals↗
PubMed1985

Thermodynamic analysis of calcium binding to frog parvalbumin.

The enthalpy of calcium binding to frog parvalbumin (Rana temporaria isoenzyme IVb, pI 4.75) has been measured by microcalorimetry. The reaction is exothermic; the heat of the reaction in 100 mM KCl, 50mM Tris, pH 8.0 at 12 degrees C is -19 kJ (mol site)-1 and -33 kJ (mol site)-1 in the presence of 1 mM magnesium. The shape of the titration curve indicates that the properties of the two calcium binding sites are different. The thermodynamic parameters measured for frog parvalbumin are compared with those of related parvalbumins from carp and whiting.

Animals↗
PubMed1984

Microcalorimetric measurement of the enthalpy of binding of rabbit skeletal myosin subfragment 1 and heavy meromyosin to F-actin.

The heat of binding of rabbit skeletal myosin subfragment 1 (myosin-S1) and heavy meromyosin (HMM) to F-actin has been measured by batch calorimetry. Proton release measurements in unbuffered solutions indicate that less than 0.1 mol of protons is absorbed or released per mol of myosin head bound to actin. Hence, the measured heats are approximately equal to the enthalpy of myosin-S1 and HMM binding to actin. The enthalpy of binding of myosin-S1 to actin was +22 +/- 3 and +27 +/- 5 kJ/mol of myosin-S1 in two series of experiments at 12 degrees C and +26 +/- 5 kJ/mol of myosin-S1 at 0 degrees C, indicating that delta Cp for this reaction in the range of 0-12 degrees C is small (-80 J/mol/K). The enthalpy of binding of HMM to actin at 12 degrees C was found to be +26 +/- 1 kJ/mol of myosin head. The enthalpies determined here and the equilibrium constants obtained from the literature for measurements at 20 degrees C under identical solvent conditions were used to estimate the entropy of the association of myosin S1 and HMM with F-actin: +235 J/mol/K for myosin-S1 and +190 J/mol of myosin head/K for HMM. Thermodynamic parameters of the interaction of myosin-S1 with actin and ADP or AMP-PNP can be evaluated using the enthalpy of association of myosin-S1 with actin determined here, together with literature values for the equilibrium constants and enthalpies of binding of these nucleotides to myosin-S1. The calculated enthalpies of binding of ADP or AMP-PNP to actomyosin-S1 are small and negative.

Actins↗