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Biomedical subjects

C L Gibbs

Publications and source records attributed to C L Gibbs.

At least 37 records · Page 2Linked to original sources
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↗
PubMed1992

Is there a shortening-heat component in mammalian cardiac muscle contraction?

It has been suggested that there is a shortening-heat component that is an extra liberation of heat on shortening above that due to the external work, which contributes to the total energy expenditure of the beating heart. The presence of a shortening heat component was studied in isolated papillary muscles from the right ventricle of rabbits killed by cervical dislocation. At the onset of a contraction, muscles were shortened from various initial lengths through fixed distances at near maximum velocity before being allowed to develop force at the new length; the heat production accompanying such contractions was measured. The measured heat was compared with heat values predicted from previously established heat-stress curves obtained by using either preshortening or latency release methods. There was no shortening-related increment in heat output per contraction when comparison was made to a control heat-stress curve, obtained using the latency release method. An increase in heat production of 10% was observed with long shortening distances when comparison was made to a control heat-stress curve obtained by preshortening the muscles; however, this difference is most likely due to an underestimate of the magnitude of the activation heat component in these control heat-stress curves. An increase in isometric heat production due to maintained stretch per se was observed. The present data indicate that it is unlikely that there is a significant shortening heat component when cardiac muscle shortens. The absence of such a metabolic component may account for the rapid fall off in total enthalpy output in isotonic contractions at low to medium afterloads when compared with the skeletal muscle data.

Analysis of Variance↗
PubMed1992

Mechanical, energetic, and biochemical changes in long-term volume overload of rabbit heart.

The mechanical and energetic consequences of long-term volume-overload (VOL) hypertrophy have been investigated in rabbits and compared with the consequence in sham-operated controls (SOC). Hypertrophy was induced by creating an aortocaval shunt, and the mechanical, biochemical, and energetic properties of the compensated heart were examined approximately 12 wk later. At 27 degrees C and a stimulus frequency of 1 Hz there were no significant changes in peak stress development, 10-90% rise times, shortening velocity, work, and mechanical power output. There was, however, a prolongation of contractile duration. The inverse relationship between peak stress and cross-sectional area was unchanged in the VOL and SOC groups. Polarographic and myothermic experiments were made on papillary muscles. Hypertrophy produced a small increment in basal metabolism. In isometric studies there were no significant changes in either the activation heat magnitude or the slope of the heat-stress relationship. In isotonic contractions there was no change in work output or total enthalpy (heat + work), and as a result mechanical efficiency was unchanged. A force-length-area (FLA) analysis of the isotonic data showed no significant change in intercept or FLA contractile efficiency. Biochemical studies showed no significant difference in the myosin isoenzyme profile at the time of death. The Ca(2+)-stimulated adenosinetriphosphatase activity of the sarcoplasmic reticulum was unchanged as were the enzymatic activities of mitochondrial citrate synthase and alpha-ketoglutarate dehydrogenase. Interestingly essentially the same data were obtained from the hearts of four animals in failure and from the hearts of seven compensated animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Altered pattern of post-rest contractions in hypertrophied rabbit ventricle.

The pattern of contractions elicited after rest periods of 0.25-10 min duration was investigated in right ventricular papillary muscles from control and hypertrophied rabbit hearts. Hypertrophy was induced by pressure overload following coarctation of the pulmonary artery. In control hearts, the first post-rest contraction was always of a smaller amplitude than the preceding steady-state (0.5 Hz stimulation) contractions, and the amplitude of this first post-rest contraction decreased as the rest interval increased. In contrast, the amplitude of the first post-rest contraction of muscles from hypertrophied hearts exceeded the steady-state amplitude for rest durations of up to at least 2 min. In the hypertrophied muscles, force in the first post-rest contraction (expressed as a percentage of the pre-rest steady-state) was potentiated compared to the control muscles at all rest intervals studied. There was no significant difference in the second post-rest contraction between control and hypertrophied muscles at any rest interval. Following the second post-rest contraction, force increased monotonically toward the steady-state levels in all the muscles. The recovery of force was, however, somewhat faster in the hypertrophied muscles. Upon resumption of 1-Hz stimulation following rest intervals of 2 min or greater, pulsus alternans were invariably observed in the hypertrophied muscles but never in the control muscles. These differences in the non-steady-state contractile behavior of ventricular muscle from normal and hypertrophied hearts are suggestive of some alteration in the normal pattern of Ca2+ translocation in pressure overload hypertrophy of rabbit ventricle.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Molecular mechanisms of memory formation.

Studies with neonate chicks, trained on a passive avoidance task, suggest that at least two shorter-term memory stages precede long-term, protein synthesis-dependent memory consolidation. Posttetanic neuronal hyperpolarization arising from two distinct mechanisms is postulated to underlie formation of these two early memory stages. Maintenance of the second of these stages may involve a prolonged period of hyperpolarization brought about by phosphorylation of particular proteins. A triggering mechanism for long-term consolidation is postulated to occur at a specific time during the second stage, and may involve reinforcement-contingent release of neuronal noradrenaline stimulating cAMP-dependent intracellular processes. The possibility that astroglia may have a critical role to play in these early stages of memory processing is raised.

Animals↗
PubMed1990

The effect of increasing extracellular potassium concentration on the resting heart rate of the isolated rat papillary muscle.

The effect of elevating extracellular K+ concentration on the basal metabolism of the isolated rat left ventricular papillary muscle has been investigated. The preparation was mounted on a thermopile and connected to a force transducer, to allow simultaneous measurement of muscle heat production and force. The resting heat rate (RHR) of the quiescent preparation was measured as an index of basal metabolism. Throughout all of the experiments, the muscles were maintained under a resting force of 10 mN and all measurements of RHR were made at times when there was no active force present above this passive level. Elevating the extracellular K+ concentration from 5.9 to 20, 40, then 80 mM produced graded increases in the RHR. The increase in RHR produced by 40 mM K+ was observed to be time-dependent, its effect being significantly greater at 5-7 h than at 2-4 h after cardiectomy. Averaged over all times, the percentage increases in RHR produced by 20, 40, and 80 mM K+ in the presence of 2 mM Ca2+ were 6.4 +/- 2.0%, 28.7 +/- 2.3%, and 51.3 +/- 8.9% (mean +/- SEM) respectively. The high K(+)-induced increase in basal metabolism was also shown to be Ca2(+)-dependent, the increase in RHR produced by 40 mM K+ being greater the higher the extracellular Ca2+ concentration (0.5-8.0 mM). The addition of verapamil was found to partially inhibit the K(+)-induced increase in resting metabolism. These results show that elevation of the extracellular K+ concentration produces a graded increase in the RHR that is Ca2(+)-dependent.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

The energy cost of relaxation in control and hypertrophic rabbit papillary muscles.

The energy cost of the onset and relaxation phases of cardiac isometric contractions has been investigated by ergometer controlled-length releases occurring at different times during the contraction cycle, to test the hypothesis that the energy cost of relaxation is normally small. Energy flux has been measured myothermically in 20 or 30 contractions of rabbit papillary muscles. The ergometer releases took place after different delays, starting during the latency period and incrementing in 50 ms steps, until eventually, releases were occurring late into the relaxation phase. The release step was kept constant and of a magnitude sufficient to prevent significant redevelopment of active stress at any release interval. The rate of release was several times greater than the maximum shortening velocity of the papillary muscle preparations. The heat production in each train of contractions was measured, but in order to estimate the total energy output, the elastic energy in the muscle-lever system which was removed by the ergometer release had to be added to the heat. This was estimated by integration of the stress-strain relationship found for each muscle. In normal animals the contraction peak, at 27 degrees C and a 1.0 Hz stimulus rate, was located between the 215 and 265 ms release times, at which point the total energy flux was estimated to be 80%-90% of that measured in a normal isometric contraction. Additional experiments were performed in a group of volume-overloaded hearts and the data were compared with results from sham-operated controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Mechanical, energetic, and biochemical changes in long-term pressure overload of rabbit heart.

The mechanical and energetic consequences of long-term pressure-overload (POL) hypertrophy have been investigated in rabbits and compared with sham-operated controls (SOC). Hypertrophy was induced by banding the pulmonary artery of young rabbits and examining the mechanical, biochemical, and energetic properties of the compensated heart 10-16 wk later. Experiments were undertaken on papillary muscles from the hypertrophic hearts. At 27 degrees C and a stimulus frequency of 1 Hz there was a modest depression of peak stress development but no significant changes in isometric rise times and one-half widths or in isotonic maximum velocity of shortening and power output. The inverse relationship between peak stress and cross-sectional area (CSA) was practically identical in the POL and SOC groups. Both polarographic and myothermic investigations were made on papillary muscles. Hypertrophy nearly halved basal metabolism, and in isometric contractions there was increased isometric economy due to a combination of a lower stress cost and a reduced activation heat. Hypertrophy did significantly depress the extent of shortening leading to a reduced work output per beat. In isotonic contractions the reduced work output was offset by a reduced energy output such that there was no significant change in suprabasal mechanical efficiency. Biochemical studies showed that the transition of myosin isoenzymes to the V3 form was essentially complete in the POL group, but that the SOC group was also predominantly V3 when the animals were killed. There was a significant 30% decline in the Ca2(+)-stimulated adenosinetriphosphatase activity of the sarcoplasmic reticulum. It is concluded that in long-term compensated hypertrophy of rabbit hearts there are only a few mechanical and energetic differences between control and hypertrophic muscles. The changes that can be detected appear to predominantly reflect disturbances in cellular Ca2+ regulation.

Animals↗
PubMed1990

Smooth muscle energetics: testing theories of crossbridge regulation.

Our results indicate that the kinetic "latch" model of Hai & Murphy is not very sensitive to the proportion of ATP assigned to crossbridges relative to that ascribed to MLC phosphorylation/dephosphorylation. Thus the basis for the relatively low efficiency of smooth muscle, attributed to high MLC phosphorylation/dephosphorylation in this model, remains open to question. Moreover, this model, or any model with mixed populations of crossbridges with differing cycle rates and/or high MLC phosphorylation/dephosphorylation rates is unlikely to account for the observed linearity of JATP and stress reported for many smooth muscles. Our studies comparing the heat production of intact and skinned smooth muscle indicate that the ATPase associated with myosin phosphorylation/dephosphorylation is unlikely to be a major factor in the tension cost of intact smooth muscle. Thus it would appear that energetics places considerable constraints on current theories of crossbridge regulation. Our modelling (Paul, 1989) suggests that it may be time to reevaluate Bozler's original hypothesis that a high attachment:detachment rate ratio for smooth muscle actin-myosin interaction may be sufficient to explain the energetics of smooth muscle.

Adenosine Triphosphate↗
PubMed1989

Energy metabolism in the perfused, arrested rabbit heart.

Energy metabolism of quiescent cardiac muscle was studied in the isolated rabbit heart preparation perfused at constant pressure by the Langendorff technique. Oxygen consumption (MVo2), coronary flow rate (CFR) and the steady state concentrations of high energy phosphate compounds were determined in hearts rendered asystolic using modified Krebs-Henseleit (KH) media containing 11 mM glucose as substrate. Basal MVo2 and CFR were significantly higher in hearts arrested by Ca2+ depletion (low Ca KH) compared to K+ excess (high K KH). Substitution of glucose in low Ca KH with a mixture containing glutamate, fumarate and pyruvate (low Ca KH + GFP) resulted in a 25% increase in the basal MVo2 but a 20% decline in CFR. Supplementing the low Ca perfusate with 30 g/l dextran (low Ca KH + dextran) depressed both the basal MVo2 (35%) and CFR (75%). Differences in the basal MVO2 under the different perfusion conditions were not accompanied by significant changes in the tissue levels of ATP, CrP or Cr. Compared to low Ca KH arrested hearts, those perfused with low Ca KH + GFP or low Ca KH + dextran did, however, show significantly lower tissue levels of ADP, AMP and Pi, but higher cytosolic ratios of [ATP]/[ADP][Pi] and [CrP]/[Cr][Pi]. As a consequence of the higher phosphorylation potential the free energy of ATP hydrolysis increased. There was no significant difference in any of these parameters between high K KH and low Ca KH perfused hearts. It is concluded that in the perfused, arrested heart none of the parameters that are used to describe the myocardial energetic state, e.g. free [ADP] or the cytosolic [ATP]/[ADP][Pi] ratio, uniquely correlates with the basal metabolic rate as estimated from MVO2 measurements.

Adenine Nucleotides↗
PubMed1988

Transducing chemical energy into mechanical function: a comparative view.

The energetics of muscle contraction can be understood in terms of the major cellular ATPases. The twitch isometric transduction efficiency is relatively constant across muscle types and species. Although many of the factors that alter the shape of the enthalpy:load relation in isotonic twitch contractions have been identified our molecular understanding is unsatisfactory and more studies are needed of mammalian muscles working closer to 37 degrees C. The thermodynamic efficiency of CB activity seems quite high, probably in excess of 70%. During maintained (tetanic) force there can be greater than a 1000 fold difference in energy usage across muscle types and there are factors that can down regulate CB activity: these factors remain to be fully identified in both skeletal and smooth muscles. The very diversity of muscle types and the different biochemical solutions that have emerged to match energy supply and demand should lead to important insights into the contractile mechanism. The corollary however also applies, it may be dangerous to take results obtained in one muscle type under a particular set of conditions, and extrapolate those findings to muscles in general.

Adenosine Triphosphatases↗