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R C Woledge

Publications and source records attributed to R C Woledge.

87 records · Page 5Linked to original sources
PubMed1975

Energy balance in DNFB-treated and untreated frog muscle.

1. Heat production and chemical changes were measured in untreated and dinitrofluorobenzene (DNFB)-treated muscles during isometric tetani. Levels of total creatine (Ct), free creatine, ATP, ADP, AMP, inorganic phosphate, glucose-1-phosphate, glucose-6-phosphate, fructose-6-phosphate, fructose-1,6-diphosphate, pyruvate, phosphoenolpyruvate, and lactate were measured. Changes in inosinic acid (IMP) were also measured. 2. DNFB effectively inhibited the creatine kinase reaction (Lohmann reaction). 3. Our major finding is that even after effective treatment with DNFB the observed heat plus work after 2 sec and 5 sec of stimulation is significantly greater than the enthalpy change produced by the measured chemical changes. This confirms that an unidentified exothermic process occurs during muscle contraction; this conclusion was reached previously from studies of untreated muscle. 4. The unexplained heat plus work is unlikely to be derived from glycolytic reactions since under anaerobic conditions no formation of lactate, pyruvate, phosphoenolpyruvate or fructose-1,6-diphosphate could be detected in either untreated or DNFB-treated muscles even 34 sec after a series of three 5 sec isometric tetani. 5. In the first 2 sec of stimulation the unexplained heat plus work is less in DNFB-treated muscles than in untreated muscles. However from 2 to 5 sec of stimulation the unexplained heat plus work is the same in treated and untreated muscles.

Adenosine Diphosphate↗
PubMed1974

Energetics of relaxation in frog muscle.

1. Changes in the levels of phosphocreatine (PCr) and ATP during relaxation after tetanic contraction have been observed and compared with the heat + work production during the same period.2. The results were the same using 2 sec or 15 sec tetani and using 15 or 30 Hz stimulation.3. During relaxation the mean chemical change (of ATP + PCr) was -0.105 +/- 0.078 mumol/g muscle (n = 53). This change is less than would be required to explain the heat + work produced.4. The PCr split during both 2 sec and 15 sec tetani (up to the last stimulus) was less than would be required to explain the heat + work produced. This confirms previous experiments.5. It is concluded that the discrepancy between chemical change and heat + work production does not diminish during relaxation but actually increases.

Adenosine Triphosphate↗
PubMed1973

The thermal effects of shortening in tetanic contractions of frog muscle.

1. In tetanic contractions during which shortening has occurred the total heat produced is greater than in isometric controls.2. The amount of this excess, measured after relaxation, is less than the shortening heat measured before relaxation. In other words relaxation heat is less after contractions with shortening.3. Only a small part of this reduction in relaxation heat can be explained by the reduced thermoelastic heat and work dissipation due to the lower tension maintained after shortening.4. In the few experiments in which the full tension is redeveloped after shortening the relaxation heat is still reduced.5. Decreases in the tension redeveloped after shortening, caused by using shorter tetani, or slower shortening, are not accompanied by decreases in the relaxation heat greater than can be accounted for by the assumed physical results of the lower tension.6. It is suggested that the reduction in relaxation heat after shortening is due to the occurrence of a reaction in which the exothermic process causing the shortening heat is reversed.

Animals↗
PubMed1971

Chemical change and energy output during muscular contraction.

1. The production of heat and (internal) work and the changes in the amount of phosphocreatine (PCr), ATP, inorganic phosphate (Pi) and sometimes lactate have been measured from moment to moment during and after tetanic isometric contractions of isolated frog muscles at 0 degrees C.2. Heat production was measured by thermopiles and a novel apparatus was employed for freezing the muscles rapidly at a chosen instant so as to halt the chemical processes before analysis.3. Using unpoisoned muscles in oxygen, it was shown that neither oxidative recovery processes nor glycolytic ones led to appreciable restitution of PCr or ATP during 15 sec of contraction. However, clear signs of recovery processes could be seen within a minute. In our preparations artificial ;ageing' by storage at low temperature did not interfere with the capacity for glycolysis.4. Our clearest result was that the break-down of PCr was not nearly large enough to account for the rapid heat production during the first few sec of contraction. By the end of a 15 sec tetanus as much as 10 mcal/g remained unaccounted for.5. The source of this heat is not clear. At no time is there any sign of net break-down of ATP; indeed there appears to be a slight increase of ATP in the stimulated muscle.6. Break-down of PCr continues both during relaxation and during the minute following, while the muscle is at rest. Thus during contraction there is heat production without PCr break-down, while subsequently there is PCr break-down without heat production.

Adenosine Triphosphate↗
PubMed1970

Heat production and chemical change in tortoise muscle.

1. Measurements have been made of heat production and changes in levels of phosphorylcreatine (PC), ATP and lactic acid resulting from contraction of tortoise muscle under anaerobic conditions.2. The only significant chemical change found was a break-down of PC.3. The amount of heat produced per mole of PC split (-DeltaH) was 13.18 +/- 1.04 kcal/mole (mean and S.E. from thirty-five observations).4. (-DeltaH) is probably rather greater in tortoise than in frog muscle. The value of (-DeltaH) cannot easily be accounted for by the known processes accompanying PC splitting in either type of muscle.

Adenosine Triphosphate↗
PubMed1968

The energetics of tortoise muscle.

1. A study has been made of the mechanical behaviour and the heat production of tortoise skeletal muscle during tetanic contractions.2. The relation between force (P) and velocity (v) is more curved than that of frog muscle. It can be fitted by Hill's equation (v/v(max) = (1 - P/P(0))/(1 + P/a)) using a value of P(0)/a considerably less than for frog muscle.3. The value of the shortening heat constant is less than in frog muscle. It is about a half of a. No evidence was found that the value depended on the load.4. The maintenance heat rate is much less than in frog muscle and, as in frog muscle, is roughly equal to a.b (where b = v(max).a/P(0)). The maintenance heat rate does not diminish during a long tetanus as it does in frog muscle.5. The ratio of work/(work + initial heat) is greater in tortoise muscle than in frog muscle. As in frog muscle, the recovery heat is about equal to (work + initial heat). It follows that tortoise muscle is more efficient than frog muscle at converting free energy into work.6. Possible theoretical bases for connexions between the shape of the force-velocity curve of a muscle and its efficiency are discussed.

Animals↗
PubMedDate not supplied

The effects of the level of activation and shortening velocity on energy output in type 3 muscle fibres from Xenopus laevis.

We investigated the effect of shortening velocity on the efficiency of single intact slow-twitch muscle fibres (type 3) of Xenopus laevis, at different levels of activation (10, 15, 20 and 40 Hz). Fused contractions were obtained at 40 Hz stimulation. When maximal isometric force had been reached, the fibres were shortened by 10% of the fibre length (L0) at 0.4, 1 and 2 L0/s. To investigate whether the oscillating force at low stimulation frequencies influenced power output and the rate of heat production, we also performed these experiments with the fibre bathed in dantrolene. The results with fused contractions in the presence of dantrolene were the same as with unfused contractions. At 40 Hz stimulation during shortening the rate of heat production increased above that measured during isometric contractions, while at the lower stimulation frequencies the rate of heat production was less than that during isometric contractions. Mechanical efficiency was highest at low activation, and increased more with shortening velocity than at high activation. The actomyosin efficiency (i.e. the efficiency corrected for "activation heat") was also highest at 10 Hz stimulation. We conclude that in slow-twitch muscle fibres of X. laevis, near the optimum shortening velocity, cross-bridge efficiency is highest for partially activated muscle.

Animals↗
PubMedDate not supplied

Activity in three parts of the quadriceps recorded isometrically at two different knee angles and during a functional exercise.

The purpose of this study was to evaluate individual differences in three parts of the quadriceps activated isometrically at 60 degrees and 90 degrees of knee flexion, and during a functional activity involving both concentric and eccentric muscle work. Surface EMG amplitudes were therefore recorded from oblique parts of vastus medialis (VMO) and vastus lateralis (VLO) and from rectus femoris (RF). VMO and VLO showed less activation at 60 degrees than at 90 degrees, but in RF there was no difference between the two angles. In the second experiment, where 11 subjects stepped on and off a stool; these amplitudes were compared with those from a maximal isometric voluntary contraction at 90 degrees of knee flexion. For VMO & VLO the normalised peak amplitude in stepping up was 1.41 +/- 0.12, & 1.46 +/- 0.15 respectively, showing that higher activity is necessary during concentric contractions. These two results suggest that the motor control of VMO/VLO may be different from the bulk of quadriceps. Our findings have implications for patellofemoral function.

Adult↗