The time-course of energy balance in an isometric tetanus.

Homsher, Earl; Kean, C. J. C.; Wallner, A; Garibian-Sarian,

doi:10.1085/jgp.73.5.553

Cited by 36 publications

(34 citation statements)

References 20 publications

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“…The present design has another advantage. The heat production in excess of that expected from PCr splitting which has been observed during rapid shortening (Rall et al 1976) occurred very early in the tetanus, when a similar 'unexplained' heat production is seen in isometric tetani (Gilbert, Kretzschmar, Wilkie & Woledge, 1971;Curtin & Woledge, 1979;Homsher, Kean, Wallner & Garibian-Sarian, 1979). This ambiguity may be removed by delaying the start of shortening until after 2 sec of isometric contraction, since heat plus work production 424 ENERGETICS OF MUSCLE SHORTENING from sources other than PCr splitting is insignificant after this time in R. pipiens muscles (as calculated by Curtin & Woledge (1978) from the results of Homsher, Rall, Wallner & Ricchiuti (1975) (Rall et al 1976).…”

Section: Introductionmentioning

confidence: 93%

“…Measurements of energy liberation were made in the 1st, 7th and 8th week of the 9 week experimental period. Heat production was measured with an electroplated thermopile (E-10, of Homsher et al 1979) from a 20 mm region near the pelvic end of each muscle pair. A 10 mm protecting region of the thermocouples (Hill, 1938), adjacent to the recording region, ensured that the heat measurements would not be affected by the type of longitudinal temperature gradients in the muscles described by Irving, Woledge & Yamada (1979).…”

Section: Introductionmentioning

confidence: 99%

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High‐energy phosphate metabolism and energy liberation associated with rapid shortening in frog skeletal muscle

Homsher

Irving

Wallner

1981

The Journal of Physiology

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SUMMARY1. High-energy phosphate metabolism and energy liberated as heat and work were measured in 3 sec tetani of frog sartorius muscles at 0 OC.2. Three contraction periods were studied: (a) shortening at near-maximum velocity for 0-3 sec from sarcomere length 2-6 to 18 sum, beginning after 2 sec of isometric stimulation, (b) the 0 7 sec isometric period immediately following such rapid shortening, (c) the period from 2 to 3 sec in an isometric tetanus at sarcomere length 1P8 um.3. There were no significant changes in levels of ATP, ADP or AMP in any contraction period. The observed changes in inorganic phosphate and creatine levels indicated that the only significant reaction occurring was phosphocreatine splitting.4. The mean rate of high-energy phosphate splitting during rapid shortening, 0-48 + 0-24 ,imole/g . sec (mean + S.E. of mean, n = 29; 'g' refers to blotted muscle weight), was not significantly different from that in the 1 sec period in the isometric tetanus, 0-32 +011 smole/g. sec (n = 17). The mean rate in the post-shortening period, 0 71 +0 10 ,umole/g . sec (n = 22), was greater than that in the 1 sec period in the isometric tetanus, and this difference is significant (P < 0-02, t test).5. A large quantity of heat plus work was produced during the rapid shortening period, but less than half of this could be accounted for by simultaneous chemical reactions. The unexplained enthalpy production was 6-5 + 26 mJ/g (mean +S.E. of mean). No significant unexplained enthalpy was produced in the 1 sec period in the isometric tetanus.6. In the post-shortening period the observed enthalpy was less, by 6-2 + 2-6 mJ/g, than that expected from the simultaneous chemical reactions.7. The results are interpreted in terms of an exothermic shift in the population of cross-bridge states during rapid shortening. It is suggested that a relatively slow subsequent step prevents many of these cross-bridges from completing the cycle and splitting ATP until after the end of shortening.

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Section: Introductionmentioning

confidence: 93%

Section: Introductionmentioning

confidence: 99%

High‐energy phosphate metabolism and energy liberation associated with rapid shortening in frog skeletal muscle

Homsher

Irving

Wallner

1981

The Journal of Physiology

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“…The following observations suggest that the labile heat is connected with processes other than actin-myosin interaction: the labile heat rate is enhanced by substances which potentiate excitation-contraction coupling (Godfraind-deBecker, 1965) and the labile heat is independent of muscle length between lo and 1-3 10 (Aubert, 1956). The labile h + w and unexplained h + w are similar in size and have similar (though not identical) time courses (Curtin & Woledge, 1979;Homsher et al 1979). Both quantities are much smaller in the second of two closely spaced tetani, whereas the tension is not much reduced (Curtin & Woledge, 1977).…”

Section: Unexplained Energy At Tmaxmentioning

confidence: 92%

“…Thus it is not surprising that the observations ofphosphocreatine give a relatively inaccurate estimate ofthe ATP usage. The value of -APCr + AATP is 9-85 + 3-58 #mol g'l dry weight for lo and 2-27 + 1-69,umol g'l dry weight for lmax If (Infante & Davies, 1965;Kushmerick & Paul, 1976;Kushmerick, 1977;Dawson, Gadian & Wilkie, 1978;Curtin & Woledge, 1979;Homsher, Kean, Wallner & Garibian-Sarian, 1979 been 802 + 35-5 mJ g-1 dry weight, which is still significantly different from zero (P < 0-05). The difference between the unexplained energy at 10 and Imax then becomes 87-9 + 46-6 mJ g-1 dry weight (P < 0 1).…”

Section: Heat and Workmentioning

confidence: 93%

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Effect of muscle length on energy balance in frog skeletal muscle.

Curtin¹,

Woledge²

1981

The Journal of Physiology

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SUMMARY1. Measurements were made of the extents of ATP splitting and the creatine kinase reaction and the heat + work (h + w) produced during 5s isometric tetani of frog semitendinosus muscle at 0'C. A comparison was made of tetani at two different muscle lengths. These lengths were lo (sarcomere length 2 3 jtm before stimulation), which is near the optimum for interaction of actin and myosin, and Imax (sarcomere length 3 8/jm) at which actin-myosin interaction is largely prevented.2. As in earlier studies of muscle at lo, the observed h + w was significantly greater than the amount explained by the energy from ATP splitting and the creatine kinase reaction. Our main new finding is that a significant amount of unexplained energy is also produced at Imax where there is a negligible amount of actin-myosin interaction.This suggests that the unexplained energy cannot be due solely to actin-myosin interaction.3. On average less unexplained energy is produced at Imax than at lo. Thus it seems likely that the process (or one of the processes) producing this energy is dependent on muscle length.4. The observed h + w was divided on the basis of its time course into the two parts, labile and stable, which were defined by Aubert (1956). The labile part of the h + w has an exponentially declining rate, and the stable part has a constant rate. The production oflabile h + w is influenced by muscle length in two ways: the total amount and the rate of its production are significantly smaller at lmax than at lo.5. At both lengths the labile h + w is equal, within experimental error, to the unexplained h + w.

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Energetics of Contraction

Barclay

2015

Comprehensive Physiology

108

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Muscles convert energy from ATP into useful work, which can be used to move limbs and to transport ions across membranes. The energy not converted into work appears as heat. At the start of contraction heat is also produced when Ca(2+) binds to troponin-C and to parvalbumin. Muscles use ATP throughout an isometric contraction at a rate that depends on duration of stimulation, muscle type, temperature and muscle length. Between 30% and 40% of the ATP used during isometric contraction fuels the pumping Ca(2+) and Na(+) out of the myoplasm. When shortening, muscles produce less force than in an isometric contraction but use ATP at a higher rate and when lengthening force output is higher than the isometric force but rate of ATP splitting is lower. Efficiency quantifies the fraction of the energy provided by ATP that is converted into external work. Each ATP molecule provides 100 zJ of energy that can potentially be converted into work. The mechanics of the myosin cross-bridge are such that at most 50 zJ of work can be done in one ATP consuming cycle; that is, the maximum efficiency of a cross-bridge is ∼50%. Cross-bridges in tortoise muscle approach this limit, producing over 90% of the possible work per cycle. Other muscles are less efficient but contract more rapidly and produce more power.

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The time-course of energy balance in an isometric tetanus.

Cited by 36 publications

References 20 publications

High‐energy phosphate metabolism and energy liberation associated with rapid shortening in frog skeletal muscle

High‐energy phosphate metabolism and energy liberation associated with rapid shortening in frog skeletal muscle

Effect of muscle length on energy balance in frog skeletal muscle.

Energetics of Contraction

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