PubMed Health⌕ Search

Biomedical subjects

C L Gibbs

Publications and source records attributed to C L Gibbs.

At least 19 recordsLinked to original sources
PubMed1998

Efficiency of skeletal and cardiac muscle.

In the human physiology literature values for skeletal and cardiac mechanical efficiency are being reported that seem to be much higher than are found in isolated tissue studies. We consider some of the different efficiency definitions and explore some possible reasons for low isolated tissue values, these include the experimental protocols used, the time at which measurements are made, afterloaded versus sinusoidal contractions, the effects of varying activation levels and recovery heat uncertainty. We examine some of the mechanical and energetic differences between cardiac and skeletal muscle--the absence of shortening heat, the linear relationship between energy per beat and pressure-volume area, constant contractile efficiency, and a larger crossbridge (CB) working stroke. Some observations are made on muscle energetics and loose and tight coupling CB models.

Biomechanical Phenomena↗
PubMed1997

Energetics of lengthening in mouse and toad skeletal muscles.

1. The energetics of lengthening were studied in amphibian and mammalian skeletal muscle. The aims were to determine whether energy absorption during stretch is a general property of skeletal muscle and to investigate the influence of lengthening velocity on energy absorption. 2. Experiments were performed in vitro (21 degrees C) using bundles of muscle fibres from fast-twitch extensor digitorum longus and slow-twitch soleus muscles of the mouse and tibialis anterior muscles of a toad, Bufo marinus. Initial heat production and mechanical work done on muscles were measured during isovelocity lengthening. Enthalpy output during lengthening was calculated as the difference between the amount of heat produced and the work done. 3. For all three muscle types, more energy was put into muscles as work than was produced as heat. Thus, part of the energy put into muscles to stretch them must have been absorbed. 4. For all three muscle types, the amount of energy absorbed was constant at velocities exceeding approximately 0.5 Vmax (Vmax is the maximum shortening velocity), but was significantly lower at slow velocities of lengthening. The same amount of energy was absorbed by all three muscles when lengthened at > or = 0.5 Vmax. 5. It was concluded that absorption of energy during lengthening occurs in mammalian as well as amphibian muscle and that lengthening velocity has only a small effect on the amount of energy absorbed.

Animals↗
PubMed1997

Age-related decline in murine macrophage production of nitric oxide.

Since certain functions mediated by nitric oxide (NO) decline with age, the age dependence of NO production by macrophages from BALB/c mice was investigated. Lipopolysaccharide-, peptidoglycan-polysaccharide-, or interferon-gamma-stimulated splenic and peritoneal macrophages from young (1 month old), middle-aged (4-5 months old), and old (6-20 months old) BALB/c mice showed a progressive and marked decline in NO production. This age-related decline in inducible NO extended to C57/BL6 and CB6F1 mice. mRNA for inducible NO synthase (iNOS), the enzyme responsible for inducible NO production by macrophages, also declined with age. Importantly, the reduced NO production by macrophages from old mice could be up-regulated by pretreating the mice with either cholera toxin or concanavalin A. These findings indicate that reduced production of NO by murine macrophages correlates directly with advancing age, likely due to deficient signals or signal transduction responsible for iNOS mRNA and protein generation.

Age Factors↗
PubMed1997

Skeletal muscle resting metabolism in cold-acclimated rats: effect of age, noradrenaline and hyperosmolarity.

1. A myothermic technique has been used to measure the resting metabolism of small bundles of a fast twitch muscle, extensor digitorum longus (EDL), and a slow twitch muscle, soleus (SOL), in 7-week-old rats. At 27 degrees C, mean (+/-SEM) resting heat rates were 2.33 +/- 0.41 and 2.09 +/- 0.37 mW/g in EDL and SOL, respectively (n = 16). 2. Seven-week-old rats were cold acclimatized at 4 degrees C for 1-4 weeks and the metabolic rates of the fast and slow twitch muscles were monitored and compared with 7- and 11-week-old controls. There was a 160% increase in metabolic rate from week 7 to week 11, but the increase also occurred in the control group. 3. In accordance with several literature reports, noradrenaline at concentrations of 10(-7) and 10(-6) mol/L had no effect on either the control or cold-acclimatized resting heat rate. 4. The osmolarity of the physiological solution bathing the muscle bundles was increased by 100 mosmol using sodium sulphate. Basal metabolism increased by similar amounts (approximately 250%) in both the fast and slow muscle bundles. Periods of cold exposure had no significant effect on the magnitude of the increment. 5. Bumetanide, a potent inhibitor of Na(+)-Cl- co-transport, produced only a slight reduction in the heat increments caused by hyperosmolar challenge.

Acclimatization↗
PubMed1996

Shortening heat in slow- and fast-twitch muscles of the rat.

Shortening heat has been reported in several amphibian skeletal muscles. In this investigation, shortening heat has been investigated in both soleus and extensor digitorum longus (EDL) muscles of young rats. The procedure involved shortening the muscles through two different distances, at near maximum velocity and at the onset of a summated twitch from different initial lengths. At the end of the shortening period, the muscle contracted isometrically, and the stress and associated heat production were recorded. These heat-stress data were compared with heat-stress data of isometric twitches at different initial lengths. There was a parallel upward shift in energy output when shortening occurred, indicating the presence of a shortening heat. Shortening heat increased with the distance shortened in soleus, but this was not the case for EDL. The values for the shortening heat coefficient for both muscle types are slightly higher than those reported for amphibian skeletal muscle and suggest that shortening heat is a significant component of the energy output of mammalian skeletal muscle.

Animals↗
PubMed1996

Mechanisms contributing to pulsus alternans in pressure-overload cardiac hypertrophy.

The mechanisms underlying pulsus alternans in pressure-over-load (POL) cardiac hypertrophy were investigated. Simultaneous measurements of force and intracellular Ca2+ (using fura 2) in right ventricular papillary muscles under conditions that produced mechanical alternans, revealed alternation of the amplitude of the Ca2+ transient together with alternation of force in some POL muscles. Instances when alternation of force occurred without any apparent alternation of the Ca2+ transient were also observed. Exposure of muscles to 5 microM ryanodine significantly attenuated mechanical alternans, thereby implicating a role for the sarcoplasmic reticulum (SR) in this process. The time course of restitution of force and the intracellular Ca2+ transient were, however, unchanged in POL hearts, indicating that SR Ca2+ cycling was not appreciably slowed. The fraction of Ca2+ recirculated intracellularly was derived from studies of postextrasystolic potentiation and was significantly reduced in the POL hearts, suggesting additional differences in cellular Ca2+ regulation. We conclude that changes in Ca2+ handling play an important role in the onset of mechanical alternans in POL hypertrophy, but that additional factors, most likely a slowing of crossbridge cycling rate, are also likely to be important.

Animals↗
PubMed1995

Fatigue and heat production in repeated contractions of mouse skeletal muscle.

1. This study tested the hypothesis that moderate fatigue of skeletal muscle arises from a mismatch between energy demand and energy supply. Fatigue was defined as the decline in isometric force. Energy supply and demand were assessed from measurements of muscle heat production. 2. Experiments were performed in vitro (21 degrees C) with bundles of muscle fibres from mouse fast-twitch extensor digitorum longus muscle and slow-twitch soleus muscle. Fibre bundles were fatigued using a series of thirty isometric tetani. Cycle duration (time between successive tetani) was 5 s. The amount of fatigue that occurred during a series of tetani was varied by varying contraction duty cycle (tetanus duration/cycle duration) by varying tetanus duration. 3. Peak isometric force and total heat production in each cycle were measured. For each cycle, the amounts of initial heat (H(i)) and recovery heat (Hr) produced were calculated and used as indices of energy use and supply, respectively. H(i) and Hr were used to estimate the net initial chemical breakdown (in energy units) in each cycle (H(i,net)). 4. The magnitude of H(i,net) was greatest in the early stages of the contraction protocol when Hr was still increasing towards a steady value. The magnitude of decline in force between successive tetani was proportional to H(i,net) for both muscles. 5. The results are consistent with the idea that the development of moderate levels of fatigue at the start of a series of contractions is due to the rate of energy supply being inadequate to match the rate of energy use.

Animals↗
PubMed1995

Mechanical determinants of myocardial oxygen consumption.

1. Recent developments which attempt to identify the mechanical determinants of myocardial oxygen consumption (mVO2) are considered, with emphasis being placed on the pressure-work and pressure-volume area (PVA) indices. 2. The difficulty of establishing a realistic in vivo basal mVO2 value is explained and the experimental reasons for the controversy over the magnitude of the activation metabolism are outlined. 3. The time varying elastance model of the heart is discussed including some current problems. The evidence for PVA as a satisfactory index of mVO2 under all physiological and pharmacological conditions is examined. Most pharmacological agents alter the intercept of the mVO2:PVA relationship but do not effect its slope: this result is interpreted to mean that the majority of current inotropic agents alter the energetic cost of calcium release/retrieval but not crossbridge efficiency. 4. An attempt is made to establish the likely cost of a cardiac contraction in man. The use of newer technology (i) to estimate mVO2 via positron emission tomography and (ii) to measure the work and potential energy output of the heart per beat with conductance catheters, is explained.

Animals↗
PubMed1995

Papillary muscles split in the presence of 2,3-butanedione monoxime have normal energetic and mechanical properties.

A number of studies have used 2,3-butanedione monoxime (BDM) to avoid myocardial damage when small muscle preparations were cut from large hearts. The present study investigates the mechanical and energetic effects of varying muscle cross-sectional area (CSA) by dissection in physiological saline containing BDM. By use of adult rat hearts, three muscle groups were obtained: whole left ventricular papillary muscles (Whole) and left ventricular papillary muscles split longitudinally in the presence of 30 mM BDM, with removal of approximately 10% (BDMSP1) or 40-50% (BDMSP2) of the muscle (5 animals in each group). The isolated muscle preparations were studied at 27 degrees C and stimulated at 0.167 Hz. The Whole and BDMSP1 preparations had comparable CSAs; in isotonically contracting muscles working against a range of afterloads, work, enthalpy (energy use), and mechanical efficiency (work/enthalpy x 100%) were similar for the two groups. In addition, isometric performance [e.g., developed stress (force/CSA), length-tension relationship, and contraction time course] was also similar for the two groups. The thinner BDMSP2 preparations showed an enhanced mechanical performance compared with the Whole and BDMSP1 groups. This outcome was in accordance with data in the literature documenting a negative correlation between stress and CSA. The results suggest that BDM-split and intact papillary muscles of similar CSA have comparable energetic and mechanical properties.

Animals↗
PubMed1993

Intracellular Ca2+, force and activation heat in rabbit papillary muscle: effects of 2,3-butanedione monoxime.

We have investigated the effects of 2,3-butanedione monoxime (BDM) and mannitol on Ca2+ metabolism in rabbit cardiac muscle. Simultaneous measurements of force and intracellular Ca2+ were made in right ventricular papillary muscles loaded with the fluorescent Ca2+ indicator fura-2. At a BDM concentration of 2 mM, peak isometric force was only 52% of control values and this was reduced to 18% at a concentration of 5 mM. The peak of the Ca2+ transient decreased by 8% at 2 mM BDM and by 18% at the higher concentration. In the presence of 362 mM mannitol peak isometric force decreased by 78% and there was a tendency for the peak of the Ca2+ transient to increase. A combination of 362 mM mannitol with 5 mM BDM completely inhibited force production despite peak Ca2+ levels that were no different from control values. In myothermic experiments under similar conditions the latency release protocol of Gibbs et al. (1988) and the BDM protocol of Alpert et al. (1989) were used to derive independent estimates of tension-independent (activation) heat in the same muscle. For both protocols the heat-stress relationship was well fitted by first-order linear regression. The activation heat estimate was significantly higher when measured with the latency release technique (2.31 mJ/g) compared with the BDM protocol (1.24 mJ/g). Our results confirm that in rabbit cardiac muscle low concentrations of BDM (2 mM) cause a marked inhibition of force development with little apparent effect on peak Ca2+ levels. Therefore, the lower activation heat estimates under these conditions may not be due to a reduced intracellular Ca2+ concentration. It is possible that the higher activation heat values obtained with protocols not involving chemical interventions may include the energy usage contributed by cellular processes that presumably do not occur in the presence of BDM and mannitol.

Analysis of Variance↗
PubMed1993

The energetics of shortening amphibian cardiac muscle.

An isolated amphibian cardiac muscle preparation, toad ventricular strip, was used to examine the energetics of shortening. Simultaneous measurements of force and length changes and the associated heat production were made. Both the isometric heat/stress and the enthalpy (heat+work)/load relationships were similar to those previously reported in mammalian cardiac muscle. The activation metabolism was higher in this preparation and, like its mammalian counterpart, was length dependent. The heat production measured in an isometric contraction was approximately 50% higher than that observed at the same stress level in rodent mammalian cardiac muscle. This did not affect the maximum isotonic mechanical efficiency (work divided by enthalpy) of the preparation which, at an afterload of 20% of the maximum stress was 18.1 +/- 1.7% (n = 8). There was no evidence for a shortening heat component in this preparation during isotonic contractions. It appears therefore that the energetics of shortening amphibian cardiac muscle closely resemble the energetics of mammalian cardiac tissue.

Animals↗
PubMed1993

Energetics of fast- and slow-twitch muscles of the mouse.

1. The energetic cost of work performance by mouse fast- and slow-twitch muscle was assessed by measuring the rates of thermal and mechanical energy liberation of the muscles at 21 degrees C. Thermal energy (heat) liberation was measured using a fast-responding thermopile. 2. Bundles of muscles fibres from the slow-twitch soleus and fast-twitch extensor digitorum longus (EDL) muscles were used. Work output was controlled by performing isovelocity shortenings during the plateau of an isometric tetanus. A range of shortening velocities, spanning the possible range, was used for each muscle. 3. During tetanic contractions, the rate of heat production from EDL muscle was 134.2 +/- 11.4 mW/g. The rate of heat production by soleus muscle was only one-fifth as great (26.8 +/- 2.7 mW/g). 4. The maximum shortening velocity (Vmax) of EDL muscles was 2.5-fold greater than that for soleus muscles and it's force-velocity relationship was less curved. Peak power output from EDL muscles was 3-fold greater than that from soleus muscle. 5. During shortening, the rate of heat output from soleus muscles increased considerably above the isometric heat rate. In contrast to soleus muscle, the rate of heat production by EDL muscle increased by only a small fraction of the isometric heat rate. The magnitude of the increases in rate was proportional to shortening velocity. 6. The total rate of energy liberation (heat rate + power) by EDL muscle, shortening at 0.95 Vmax was 1.62 +/- 0.37 times greater than the isometric heat rate. In contrast, the rate of energy liberation from soleus muscle shortening at 0.95 Vmax was 5.21 +/- 0.58 times greater than its isometric heat rate. The peak mechanical efficiency (power/total energy rate) of the both muscles was approximately 30%.

Animals↗
PubMed1992

Plasmid cDNA-directed protein synthesis in a coupled eukaryotic in vitro transcription-translation system.

A system is described in which transcription of cDNA clones by bacteriophage T7 RNA polymerase is coupled to translation in the micrococcal nuclease treated rabbit reticulocyte lysate in a single reaction of coupled transcription-translation. The monovalent and divalent cation requirements for translation are dominant for optimum expression in this coupled system, so that transcription is relatively inefficient. Nevertheless, the use of appropriate DNA concentrations leads to the synthesis of sufficient RNA to saturate the protein synthesis capacity of the system. The fidelity and efficiency of expression in this coupled system are high, and the degree of purification of the plasmid DNA is relatively uncritical. The system therefore offers very considerable advantages for rapid screening of 'mini-preparations' of cDNA plasmid constructs for retention of the correct reading frame and expression of the desired protein product.

Animals↗
PubMed1992

Mechanical and energetic changes in short-term volume and pressure overload of rabbit heart.

The mechanical and energetic consequences of a short-term volume overload (STVOL) hypertrophy and short-term pressure overload (STPOL) hypertrophy have been investigated in rabbits and compared with short-term sham-operated controls (STSOC). Hypertrophy was induced either by creating an aortocaval shunt (volume overload) or by banding the pulmonary artery (pressure overload). Suitable papillary muscles were excised from the hearts 8-10 days after the surgical procedure. At 27 degrees C and a stimulus frequency of 1.0 Hz, peak stress development of the STVOL preparations was significantly reduced from the control group, whereas no significant difference in peak stress development was evident between the STPOL and STSOC groups. Surprisingly, the STPOL preparations displayed pulsus alternans after only 8-10 days of inducing the overload. At steady-state conditions, the isometric 10%-90% rise times, the 90%-10% relaxation times, and the 1/2-widths were not significantly different between the treated and control groups. In isotonically contracting muscles working against a range of afterloads, the enthalpy (energy) and work output of the STVOL and STPOL preparations were depressed compared to the STSOC preparations; the differences were statistically significant for the STVOL group. Due to the parallel change in work and enthalpy, the mechanical efficiency was unaltered. A force-length-area (FLA) analysis, analogue of the pressure-volume-area (PVA) analysis, was applied to the isotonic data of this study. The isotonic enthalpy at the various load levels was plotted against the measured FLA and the data were fitted by linear regression. It was evident that the FLA correlated closely with the energy used. The STVOL and STPOL mean total energy:FLA regression lines lay parallel to but were below the STSOC line, signifying a drop in the activation heat, although this reduction did not achieve statistical significance. It is concluded that significant mechanical and energetic changes are evident after a short-term volume overload although earlier work has shown that these differences are absent at the later, compensated stage of hypertrophy. Changes associated with the pressure overload model suggest a disturbance in calcium regulation: this effect is also seen in long-term pressure overload.

Animals↗