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C L Gibbs

Publications and source records attributed to C L Gibbs.

At least 73 records · Page 4Linked to original sources
PubMed1978

Cardiac energetics.

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Adenosine Triphosphate↗
PubMed1976

Recovery heat production of mammalian fast- and slow-twitch muscles.

Relationships between initial heat and recovery heat in fast-twitch extensor digitorum longus (EDL) and slow-twitch soleus (SOL) muscles of the rat have been investigated by estimating the ratio of total heat (initial + recovery) to estimated initial heat. Results obtained from SOL agreed well with earlier data from amphibian skeletal muscle and indicated that in tetanic contractions of SOL the ratio,total heat/initial heat, was slightly greater than 2. Experiments on EDL revealed complexities not previously reported for amphibian muscle. Anaerobic total heat production by EDL was as much as 75% of aerobic heat production. When the initial heat was estimated under anaerobic conditions and with iodacetate present, the apparent ratio of total heat/initial heat in tetanic contractions of EDL approached a value of 2. The results are discussed in relation to the enzymatic characteristics of these muscles, and it is suggested that the recovery heat of SOL arises mainly from mitochondrial oxidative metabolism while that of EDL arises, to a large extent, from glycolytic activity.

Aerobiosis↗
PubMed1975

Structural, mechanical and myothermic properties of rabbit rectococcygeus muscle.

1. The fine structure of rabbit rectococcygeus muscle has been studied with the electron microscope. 2. The mechanical performance and the heat production of this muscle has been investigated during tetanic contractions at 27 degrees C. 3. In isometric contractions a force of 164 +/- 27 mN/mm2 (mean +/- S.D., n = 17) is developed and the heat production is linearly related to the force. 4. There is a relationship between the duration of stimulation (t) and the total heat production (H) of the type H = A plus bt, where A and b are constants. 5. After-loaded isotonic experiments show that the relationship between force and velocity can be fitted by the 'characteristic equation' of Hill (1938). 6. The value of a/P0 (0-302 +/- 0-093, mean +/- S.D.) is slightly higher than in frog skeletal muscle but the constant b is about 50 times smaller. 7. The ratio of work/total energy production, for the stimulus conditions employed, was maximally 0-185. 8. The ratio of total enthalpy to initial enthalpy is difficult to measure accurately but is probably about 2.

Animals↗
PubMed1975

Fluorometric and myothermic studies of cardiac energetics.

Energy production during isometric and isotonic contractions of cardiac muscle has been studied using the isolated papillary muscle of the rabbit at room temperature. Muscles were mounted on thermopiles to record heat production associated with small numbers of contractions and then were mounted in an organ bath for fluorometric recording of the level of reduction of mitochondrial NAD. After each twitch there was a decrease in the level of fluorescence followed by an exponential return to the resting level, or further decreases after subsequent twitches. The fluorescence-time integral (integral delta Fl-dt), or area enclosed by a fluorometric transient during and after a series of twitches, was found to vary in magnitude in a manner similar to the magnitude of the total heat production when the mechanical conditions of contraction were altered by varying the load. The influence of the metabolic state of the muscle was also studied by using either glucose or sodium pyruvate as the exogenous substrates in the bathing medium. When pyruvate was substituted for glucose, maximum external work, maximum isometric force, and maximum mechanical efficiency were all increased. The kinetics of oxidative recovery metabolism, either measured fluorometrically or derived from the heat production, was accelerated when pyruvate replaced glucose.

Animals↗
PubMed1972

Energetics of isometric and isotonic twitches in toad sartorius.

Contractile energetics have been studied in twitches of toad sartorius muscle at 6-7 degrees C. Isometric and isotonic energy production has been measured and plotted against a wide range of developed tensions and tension-time integrals. These parameters were varied by altering the isotonic load or by changing the preset isometric length. The isometric tension-independent heat was 1.12 +/-0.18 (SD) mcal/g. The isometric heat coefficient Pl(0)/H was 12.0 +/-1.4 in muscles having twitch to tetanus ratios ranging from 0.4 to 0.6. Isometric enthalpy increased monotonically with tension or tension-time integral but the correlation between isometric heat and these parameters was poor. Isotonic enthalpy consumption was always higher than isometric enthalpy for any given tension or tension-time integral; however, isotonic heat production was consistently less than isometric heat production. The isotonic heat for the highest load (3 g) was not significantly different from the isometric tension-independent heat. Thus isotonic heat production first decreased and then increased with increasing tension or tension-time integral. In the discussion it is shown that the results conflict with all current interpretations of muscle energetics.

Animals↗
PubMed1972

An energetic model of muscle contraction.

Initial energy utilization in the twitch is visualized as the result of the activity of two distinct processes. The first is the calcium-pumping activity of the sarcoplasmic reticulum, which has a constant energy requirement under normal conditions. The second is the chemomechanical transduction process consisting of a variable number of quantal contractile events, each with a fixed enthalpy equal to the molecular enthalpy of adenosine triphosphate (ATP) hydrolysis in vivo. This enthalpy appears either as heat or as contractile element work. Total enthalpy varies according to the number of quantal contractile events that occur in the twitch cycle. The basis of the variation is suggested to be velocity-dependent activity of the actomyosin ATPase, allowing more quantal events to occur in a contraction cycle when shortening occurs. The classical designation "activation heat" is held to be appropriate for the first process. The partition of the enthalpy of the second process that is currently in vogue is held to be misleading and a new formulation is suggested in which the properties of the quantal contractile event are reflected in general terms. The formulation of the proposed transduction model represents a conceptual return to the viscoelastic theory, but at a quantal level. The model can explain the results of the preceding paper and is adaptable to different muscles without having to postulate fundamental differences in energy utilization.

Actomyosin↗
PubMed1970

Energy production in cardiac isotonic contractions.

The energy output of rabbit papillary muscle is examined and it is shown that there is more energy liberated in an afterloaded isotonic contraction than in an "equivalent" isometric contraction. This statement holds true regardless of whether equivalence is based on the proposition that tension or the time integral of tension is the best index of muscle energy expenditure. Besides the external work performed there is additional heat production in isotonic contractions and this heat increases as the afterload is decreased. The additional heat is more evident when tension rather than the time integral of tension is made the determinant of energy expenditure. It is shown in single contractions that the rate of isotonic heat production, regardless of afterload size, never exceeds the heat rate recorded in an isometric contraction at the same initial length. Experiments reveal no simple linear correlation between isotonic energy output and contractile element work. Problems associated with the compartmentalization of the energy output of a contraction are discussed.

Analysis of Variance↗