ATP,creatine phosphate,and mechanical activity in rainbow trout myocardium under inhibition of glycolysis and cell respiration

Summary Twitch force and resting tension of electrically stimulated ventricular strips of rainbow trout were compared with tissue contents of phosphocreatine, creatine, and ATP. The phosphocreatine/total creatine ratio, which was used to assess the cytoplasmic phosphorylation potential, fell with the fraction of cell respiration that was inhibited by sodium cyanide and N₂. Concomitantly, twitch force decreased while resting tension tended to increase. This relation between phosphocreatine/total creatine and mechanical parameters became more prominent as glycolysis was increasingly inhibited by sodium iodoacetate. Furthermore, glycolytic inhibition was followed by a decrease in the ATP/phosphocreatine ratio. The latter effect was the same in 1% and 6% CO₂. Thus, it cannot be ascribed to an action of intracellular pH on the creatine kinase catalyzed reaction. Notably, resting tension as well as twitch force relative to ATP was augmented by glycolytic inhibition. The main conclusions are that in the presence of a decreased mitochondrial activity, glycolysis protects contractility not only by counteracting a lowering in high energy phosphates but also by supporting the ATP/phosphocreatine ratio. Apparently, the creatine kinase activity is insufficient to maintain ATP in equilibrium with phosphocreatine. In addition, glycolysis seems to elevate the level of free phosphate relative to ATP, so that twitch force development as well as rigor complex formation is counteracted.     

Acidosis counteracts the negative inotropic effect of K+ on ventricular muscle strips from the toad Bufo marinus

Strenuous activity is associated with acidosis, increased extracellular potassium concentration ([K+]o), and elevated levels of circulating catecholamines. Acidosis and elevated [K+]o are normally considered harmful to cardiac function, and a high sympathetic tone on the heart may lead to arrhythmia. During activity, however, the heart must be able to increase rate and strength of contraction. While the individual effects of [K+]o, acidosis, and adrenaline on contractile properties of cardiac muscle have been characterized for some ectothermic species, less information is available on their interactions. Here we examine the isolated and combined effects of [K+]o, acidosis, and adrenaline on ventricular muscle strips from the toad Bufo marinus. This study showed that increased [K+]o significantly reduced twitch force, while lactic acid significantly increased twitch force and more than counteracted the negative inotropic effects of elevated [K+]o. There was no inotropic effect of Na-lactate (neutralized lactic acid), which suggests that lactic acid stimulated twitch force through reduced pH and not by serving as a substrate. Adrenaline had a positive effect on twitch force in all preparations. Irrespective of treatment, twitch force decreased as stimulation rate increased. During high [K+]o, there was a severe reduction in maximal frequency of toad ventricular strips that was not alleviated by lactic acidosis and/or adrenaline, which suggests that high [K+]o influences twitch force and maximal rate by different mechanisms. In vivo levels of lactic acid, [K+]o, adrenaline, and heart rate previously observed during forced activity in Bufo did not significantly affect the contractile properties of heart muscle strips in vitro. Thus, although [K+]o significantly decreased twitch force, this detrimental effect was more than counteracted by the positive inotropic effect of lactic acid and adrenaline.     

Temperature,contractility and high energy phosphates in anoxic fish heart muscle

Summary Isolated, electrically paced ventricular tissue of rainbow trout, Oncorhynchus mykiss, was examined at 20 and 10°C for the effects of different metabolic inhibitions on isometric force development and cellular content of phosphocreatine, creatine, ATP, ADP and AMP. At 20 relative to 10°C, twitch force was the same, but both twitch development and relaxation occurred over a shorter time and at a considerably higher maximal rate. Inhibition of cellular respiration caused twitch force and phosphocreatine to decrease, both about twice as fast at 20 as at 10°C. This doubling of energy degradation, i.e. in decrease of phosphocreatine, ATP, and loss of twitch force also occurred in preparations in which the energy liberation was totally blocked by iodoacetate in combination with N₂ and cyanide; both anaerobic energy degradation and anaerobic energy liberation expressed as lactate production were doubled. The similar effect of temperature on degradation and liberation of energy might explain why loss of twitch force during a 1-h period of anoxia was the same at both temperatures. The latter result was also found in the myocardium of eel Anguilla anguilla. In spite of its large influence on the time-course of twitch force development, the difference in temperature had no evident effects on the relationship between twitch force and phosphocreatine.Abbreviation Cr_t total creatine (creatine and phosphocreatine) - EDTA ethylenediminetetra-acetate - IAA iodoacetate - PCr phosphocreatine - TPT time-to-peak force - TR ₇₅ time for relaxation - V _F maximal rate of force development - V _R maximal rate of relaxation     

Energy metabolism of fast- and slow-twitch skeletal muscle in the rat: Thyroid hormone induced changes

Summary Male Wistar rats were made hypothyroid or hyperthyroid over a period of six weeks, by administration of carbimazole or triiodothyronine (T₃). Serial frozen sections of soleus and extensor digitorum longus (EDL) muscle were stained histochemically for myosin ATPase, succinic dehydrogenase and phosphorylase. Muscle fibres were classified as either slow twitch oxidative (SO), fast twitch oxidative glycolytic (FOG) or fast twitch glycolytic (FG). In addition the activities of phosphorylase, phosphofructokinase (PFK), fructose-1,6-diphosphatase (FDP), lactate dehydrogenase (LDH), hexokinase, citrate synthetase, cytochrome oxidase, 3-hydroxyacyl-CoA dehydrogenase (HAD) and 5-AMP aminohydrolase were measured in both muscles.Increasing plasma levels of T₃ are associated with marked alterations in the fibre type populations in both muscles. In the soleus there is conversion of SO to FOG fibres while in the EDL, FG fibres are converted to FOG fibres. The quantitative changes in metabolic enzyme activity however, are in the main restricted to the soleus. Increased T₃ levels result in an increased capacity for the aerobic metabolism of both fat and carbohydrate and an increase in anaerobic glycolytic activity in the soleus muscle which parallels the change in fibre types. However, the extent of these increases cannot be explained solely on this basis and there is also an overall increase in aerobic activity in all fibres including slow oxidative ones. It is concluded that the effects of thyroid hormone on muscle phenotype and respiratory capacity involve both primary and secondary sites of action and the possible mechanisms are discussed.Abbreviations EDL extensor digitorum longus - FDP fructose-1,6-diphosphatase - FG fast twitch glycolytic - FOG fast twitch oxidative glycolytic - HAD 3-hydroxyacyl-CoA-dehydrogenase - LDH lactate dehydrogenase - PFK phosphofructokinase - SO slow twitch oxidative - T ₃ triiodothyronine - T ₄ thyroxine     

Catabolic enzyme activities in relation to premigratory fattening and muscle hypertrophy in the gray catbird (Dumetella carolinensis)

Summary The flight muscles of the gray catbird (Dumetella carolinensis) were examined to determine if short term adjustments occur in the activity of key catabolic enzymes during preparation for long distance migration. The aerobic capacity of the pectoralis muscle as indicated by citrate synthase activity (CS) is among the highest reported for skeletal muscle (200 moles [min·g fresh mass]^–1 at 25°C). The mass specific aerobic capacity as indicated by CS activity or cytochromec concentration does not change during premigratory fattening (Fig. 2) or in relation to the muscle hypertrophy that occurs concomitantly. The maintenance of mass specific aerobic capacity indicates that the total aerobic capacity increases in proportion to the increase in muscle size. The augmented potential for total aerobic power output is considered an adaptation to meet the increased power requirements of flight due to the increased body mass. Additionally, the capacity to oxidize fatty acids, as indicated by -hydroxyacyl-CoA dehydrogenase activity, approximately doubles during premigratory fattening (from 35 to 70 moles [min·g fresh mass]^–1 at 25°C; Fig. 1A). This adaptation should favor fatty acid oxidation, thereby sparing carbohydrate and prolonging endurance. The activity of phosphofructokinase, a key glycolytic enzyme, does not change before migration.Abbreviations CPT carnitine palmitoyl transferase - CS citrate synthase - HOAD -hydroxyacyl-CoA-dehydrogenase - PFK phosphofructokinase     

Extracellular determinants of cardiac contractility in the cold anoxic turtle

Painted turtles (Chrysemys picta) survive months of anoxic submergence, which is associated with large changes in the extracellular milieu where pH falls by 1, while extracellular K+, Ca++, and adrenaline levels all increase massively. While the effect of each of these changes in the extracellular environment on the heart has been previously characterized in isolation, little is known about their interactions and combined effects. Here we examine the isolated and combined effects of hyperkalemia, acidosis, hypercalcemia, high adrenergic stimulation, and anoxia on twitch force during isometric contractions in isolated ventricular strip preparations from turtles. Experiments were performed on turtles that had been previously acclimated to warm (25 degrees C), cold (5 degrees C), or cold anoxia (submerged in anoxic water at 5 degrees C). The differences between acclimation groups suggest that cold acclimation, but not anoxic acclimation per se, results in a downregulation of processes in the excitation-contraction coupling. Hyperkalemia (10 mmol L(-1) K+) exerted a strong negative inotropic effect and caused irregular contractions; the effect was most pronounced at low temperature (57%-97% reductions in twitch force). Anoxia reduced twitch force at both temperatures (14%-38%), while acidosis reduced force only at 5 degrees C (15%-50%). Adrenergic stimulation (10 micromol L(-1)) increased twitch force by 5%-19%, but increasing extracellular [Ca++] from 2 to 6 mmol L(-1) had only small effects. When all treatments were combined with anoxia, twitch force was higher at 5 degrees C than at 25 degrees C, whereas in normoxia twitch force was higher at 25 degrees C. We propose that hyperkalemia may account for a large part of the depressed cardiac contractility during long-term anoxic submergence.     

Maintenance of resting tension in the american eel (Anguilla rostrata L.) heart is dependent upon exogenous fuel and the sarcoplasmic reticulum

The relationship between extracellular glucose and management of cell Ca(2+) in the heart of the American eel (Anguilla rostrata) was indirectly assessed by monitoring the performance of isolated ventricular strips at 20 degrees C. Twitch force increased in ventricular strips under specific conditions of 30 bpm pacing and an extracellular Ca(2+) challenge from 1.5 to 9.5 mM. The response was independent of any exogenous metabolic fuel in the medium. Resting tension was maintained when glucose was available, but in the absence of a metabolic fuel, resting tension increased in response to the increase in extracellular Ca(2+) level. When ventricular strips were treated with iodoacetate to inhibit glycolysis, a Ca(2+) challenge resulted in a decrease in twitch force in association with an approximately equivalent increase in resting tension even in the presence of exogenous glucose. However, when pyruvate (5 mM) was substituted as a metabolic fuel, twitch force increased as a function of extracellular Ca(2+), and resting tension was maintained in the presence of iodoacetate. Therefore, there is a need for an extracellular fuel but not a specific metabolic requirement for glucose to maintain the performance characteristics, which are presumably related to the management of intracellular Ca(2+) levels. Ventricular strips were treated with ryanodine to inhibit Ca(2+) release and uptake by the sarcoplasmic reticulum (SR). Ryanodine treatment impaired postrest potentiation at high extracellular Ca(2+) levels. In the presence of ryanodine, the protective effect of glucose on the increase in resting tension in the face of an extracellular Ca(2+) challenge was eliminated. Considered together, the results reveal that the heart of the American eel has a requirement for an extracellular fuel to manage intracellular Ca(2+) at high Ca(2+) loads, and that the SR plays a role in the beat-to-beat regulation of Ca(2+) at a frequency of 30 bpm, high Ca(2+) load, and 20 degrees C.     

Reproducible measurement of voluntary activation of human elbow flexors with motor cortical stimulation.

Voluntary activation of muscle is commonly quantified by comparison of the extra force added by motor nerve stimulation during a contraction [superimposed twitch (SIT)] with that produced at rest by the same stimulus (resting twitch). An inability to achieve 100% voluntary activation implies that failure to produce maximal force output from the muscle must have occurred at a site at or above the level of the motoneurons. We have used cortical stimulation to quantify voluntary activation. Here, incomplete activation implies a failure at or above the level of motor cortical output. With cortical stimulation, it is inappropriate to compare extra force evoked during a contraction with the twitch evoked in resting muscle because motor cortical and spinal cord excitability both increase with activity. However, an appropriate "resting twitch" can be estimated. We previously estimated its amplitude by extrapolation of the linear relation between SIT amplitude and voluntary torque calculated from 35 contractions of >50% maximum (Todd G, Taylor JL, and Gandevia SC. J Physiol 551: 661-671, 2003). In this study, we improved the utility of this method to enable evaluation of voluntary activation when it may be changing over time, such as during the development of fatigue, or in patients who may be unable to perform large numbers of contractions. We have reduced the number of contractions required to only three. Estimation of the resting twitch from three contractions was reliable over time with low variability. Furthermore, its reliability and variability were similar to the resting twitch estimated from 30 contractions and to that evoked by conventional motor nerve stimulation.     

Differential effects of fatty acids on glycolysis and glycogen metabolism in vascular smooth muscle

The effects of fatty acids of different chain lengths on aerobic glycolysis, lactic acid production, glycogen metabolism and contractile function of vascular smooth muscle were investigated. Porcine carotid artery segments were treated with 50 microM iodoacetate and perchloric acid tissue extracts were then analyzed by 31P-NMR spectroscopy to observe the accumulation of phosphorylated glycolytic intermediates so that the activity of the Embden-Myerhof pathway could be tracked under various experimental paradigms. Aerobic glycolysis and lactate production in resting arteries were almost completely inhibited with 0.5 mM octanoate, partially inhibited with 0.5 mM acetate and unaffected by 0.5 mM palmitate. Inhibition of glycolysis by octanoate was not attributable to inhibition of glucose uptake or glucose phosphorylation. Basal glycogen synthesis was unchanged with palmitate and acetate, but was inhibited by 52% with octanoate incubation. The characteristic glycogenolysis which occurs upon isometric contraction with 80 mM KCl in the absence of fatty acid in the medium was not demonstrable in the presence of any of the fatty acids tested. Glycogen sparing was also demonstrable in norepinephrine contractions with octanoate and acetate, but not with palmitate. Additionally, norepinephrine-stimulated isometric contraction was associated with enhanced synthesis of glycogen amounting to 6-times the basal rate in medium containing octanoate. Contractile responses to norepinephrine were attenuated by 20% in media containing fatty acids. Thus, fatty acids significantly alter metabolism and contractility of vascular smooth muscle. Fatty acids of different chain lengths affect smooth muscle differentially; the pattern of substrate utilization during contraction depends on the contractile agonist and the fatty acid present in the medium.     

Role of glycolysis in the relaxation process in mammalian cardiac muscle: comparison of the influence of glucose and 2-deoxyglucose on maintenance of resting tension

This study explores the effect of glucose on resting tension in mammalian cardiac muscle. Exogenous glucose (5 mM) ameliorates the increase in resting tension seen in severely hypoxic cardiac muscle. This effect of glucose is independent of any influence on total adenosine triphosphate (ATP) concentration, and cannot be duplicated with 2-deoxyglucose. Resting tension remains stable in muscles exposed to 1 mM iodoacetate (IAA) under aerobic conditions; contracture occurs rapidly when IAA exposed preparations are made severely hypoxic. These observations suggest that glycolysis is sufficient but not necessary for the maintenance of stable resting tension under our experimental conditions. While it is not clear from these data that glycolytically produced ATP is used preferentially, the possibility that a small compartment of ATP is supplied to the relaxing system is clearly suggested.     

Glucose catabolism during aging and differentiation in hypocotyls ofPhaseolus mungo seedlings

Changes in activities of the glycolytic and pentose phosphate (PP) pathways in glucose catabolism in various parts of the hypocotyls obtained from 4-day-old etiolatedPhaseolus mungo seedlings were investigated by measuring the inhibition rates of respiration by iodoacetate and malonate, and the release of¹⁴CO₂ from [1-¹⁴C]- and [6-¹⁴C]glucose. The relative activity of the PP pathway in glucose catabolism was higher in the immature part (Part I) and the aged part (Part V) of the hypocotyls than in the intermediary one (Part III), while the activity of the glycolytic pathway decreased with aging. On a fresh weight basis, the enzyme activities of the glycolytic and PP pathways were higher in Part I than in Parts III and V. On a protein content basis, however, activities of the enzymes of the PP pathway increased with aging and differentiation of the hypocotyls whereas those of the glycolytic pathway decreased. Levels of nicotinamide adenine nucleotides were found to be in the following order: Part I>Part III> Part V for NAD⁺+NADH; Part I>Part V>Part III for NADP⁺+NADPH. The stimulative effect of methylene blue on decreasing the C₆/C₁ ratio was greater in Part III than in Part I, and No effect was observed in Part V. These data suggest that a decrease in the activity of the glycolytic pathway with aging and differentiation may be due to the decreasing glycolytic enzyme activities and NAD(H) content. The higher activity of the PP pathway in the immature part is attributable to larger amounts of NADP(H) and enzymes of the PP pathway. The greater contribution of the PP pathway to glucose catabolism in the aged part than in the intermediary part seems to results from a more active turnover of NADP and the relatively higher activity of the enzymes of the PP pathway than those of the glycolytic pathway.     

Glyceraldehyde-3-phosphate dehydrogenase has no control over glycolytic flux in Lactococcus lactis MG1363

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) has previously been suggested to have almost absolute control over the glycolytic flux in Lactococcus lactis (B. Poolman, B. Bosman, J. Kiers, and W. N. Konings, J. Bacteriol. 169:5887-5890, 1987). Those studies were based on inhibitor titrations with iodoacetate, which specifically inhibits GAPDH, and the data suggested that it should be possible to increase the glycolytic flux by overproducing GAPDH activity. To test this hypothesis, we constructed a series of mutants with GAPDH activities from 14 to 210% of that of the reference strain MG1363. We found that the glycolytic flux was unchanged in the mutants overproducing GAPDH. Also, a decrease in the GAPDH activity had very little effect on the growth rate and the glycolytic flux until 25% activity was reached. Below this activity level, the glycolytic flux decreased proportionally with decreasing GAPDH activity. These data show that GAPDH activity has no control over the glycolytic flux (flux control coefficient = 0.0) at the wild-type enzyme level and that the enzyme is present in excess capacity by a factor of 3 to 4. The early experiments by Poolman and coworkers were performed with cells resuspended in buffer, i.e., nongrowing cells, and we therefore analyzed the control by GAPDH under similar conditions. We found that the glycolytic flux in resting cells was even more insensitive to changes in the GAPDH activity; in this case GAPDH was also present in a large excess and had no control over the glycolytic flux.     

Microbial sensors for determination of aromatics and their chloroderivatives. Part II: Determination of chlorinated phenols using a Rhodococcus-containing biosensor

An amperometric biosensor for determination of phenol and chlorophenols using Rhodococcus has been developed. This sensor is more sensitive to phenol and chlorophenols, especially to mono- and dichlorinated phenol, than to benzoate and monochlorobenzoates. The incubation of the sensor with phenol and its chlorinated derivatives enhanced the activity of the microbial sensor for these compounds. A linear relationship between the current range and the concentration of phenol, 2-, 3- and 4-chlorophenol was observed up to 20 mol/l. The detection limit for all studied substrates was 4 mol/l. The current difference was reproducible within 5.5% when the test solution contained 40 mol phenol/l. Correspondence to: K. Riedel     

Tungstate does not support synthesis of active formylmethanofuran dehydrogenase in Methanosarcina barkeri

Cell extracts of Methanosarcina barkeri grown on methanol in media supplemented with molybdate exhibited a specific activity of formylmethanofuran dehydrogenase of approximately 1 U (1 mol/min)/mg protein. When the growth medium was supplemented with tungstate rather than with molybdate, the specific activity was only 0.04 U/mg. Despite this reduction in specific activity growth on methanol was not inhibited. An inhibition of both growth and synthesis of active formylmethanofuran dehydrogenase was observed, however, when H₂ and CO₂ were the energy substrates. The results indicate that, in contrast to Methanobacterium wolfei and Methanobacterium thermoautotrophicum, M. barkeri possesses only a molybdenum containing formylmethanofuran dehydrogenase and not in addition a tungsten isoenzyme.     

Cardiac force-interval relationship,adrenaline and sarcoplasmic reticulum in rainbow trout

The force-interval relationship was examined at 20 and 10 °C in electrically paced atrial and ventricular tissue of rainbow trout,Oncorhynchus mykiss, regarding dependence on the sarcoplasmic reticulum and influence of adrenaline. In both tissues, adrenaline (10^-6 mol·l^-1) doubled control force developed at 0.5 Hz. In atrial but not in ventricular tissue it also shortened the diastolic interval needed for recovery of a given fraction of the control force. In atrial tissue and in ventricular tissue at 20 °C, the fraction of force recovered in the presence of adrenaline was diminished by 10 mol·l^-1 of ryanodine, a specific inhibitor of the sarcoplasmic reticulum. In atrial tissue not exposed to adrenaline and in ventricular tissue at 10 °C irrespective of adrenaline, ryanodine did not affect recovery. In atrial but not in ventricular tissue it also diminished control force. In conclusion, the cardiac sarcoplasmic reticulum of trout seems to support force development during adrenaline dependent increases in heart rate, and in atrial tissue also the force at steady state.Abbreviations E-C coupling excitation-contraction coupling - P-R potential - SR sarcoplasmic reticulum - SE standard error of the mean     

Integrating the Physiology, Mechanics and Behavior of Rapid Running Ghost Crabs: Slow and Steady Doesn't Always Win the Race

In 1979 Bliss predicted that, "land crabs are and will undoubtedlycontinue to be promising objects of scientific research." Studiesof rapid running ghost crabs support her contention and haveresulted in several general findings relating to locomotionand activity. 1) Energy exchange mechanisms during walking aregeneral and not restricted to quadrupedal and bipedal morphologies.2) "Equivalent gaits," such as trots and gallops, may existin 4-, 6- and 8-legged animals that differ greatly in leg andskeletal (i.e., exo- vs. endoskeletal) design. These findingssupport the hypothesis that terrestrial locomotion in many speciescan modeled by an inverted pendulum or spring-mass system. 3)An open circulatory system and chitin-covered gills do not necessarilylimit the rate at which oxygen consumption can be increasedor the factorial increase oxygen consumption over resting rates.4) Interspecific and intraspecific i.e., ontogenetic) scalingof sub-maximal oxygen consumption and maximal aerobic speedcan differ significantly. 5) Locomotion at speeds above themaximal aerobic speed requiring non-aerobic contributions maybe far more costly than can be predicted from aerobic costsalone. The cost transport may attain a minimum at less thanmaximum speed. 6) The speed which elicits maximal oxygen consumptionduring continuous exercise is attained at moderate walking speedsin crabs and probably other ectotherms. Speeds 15- to 20-foldfaster are possible, but cannot be sustained. 7) The low enduranceassociated with the low maximal oxygen consumption and maximalaerobic speed of ectotherms moving continuously can be increasedor decreased by altering locomotor behavior and moving intermittently.Ectotherms can locomote at high speeds and travel for considerabledistances or remain active for long periods by including restpauses. Alternatively, intense activity with extended exerciseperiods with short pause periods may actually reduce behavioralcapacity or work accomplished relative to continuous activityduring which the behavior is carried out at a lower intensitylevel without pauses.     

Relationship between exogenous fuel availability and performance by teleost and elasmobranch hearts

Summary Performance by perfused isolated hearts of sea raven (Hemitripterus americanus) and skate (Raja erinecea), representatives of teleost and elasmobranch fishes, respectively, was monitored over a 30 min period under conditions of variable metabolic fuel availability. In both preparations initial cardiac output and hence fuel delivery to the myocardia were comparable to in vivo levels. Pressure development and hence overall work rate of the sea raven heart was also similar to in vivo levels.Fuel deprived sea raven hearts entered into a modest but significant contractile failure which could be prevented by the inclusion of 10 mM glucose or 1.0 mM palmitate in the perfusion medium. Addition of the glycolytic inhibitor iodoacetate to the medium resulted in rapid heart failure. Performance in the presence of iodoacetate could be improved by the inclusion of palmitate, lactate, or acetoacetate in the perfusion media but only high physiological levels of palmitate could completely alleviate the effect of iodoacetate.The inclusion of 1.0 mM palmitate in the perfusion medium of skate hearts resulted in a significant decrease in performance relative to fuel deprived hearts. Addition of iodoacetate to the medium resulted in rapid contractile failure. Hearts perfused with medium containing both iodoacetate and acetoacetate performed as well as fuel deprived hearts, indicating that this ketone body is an effective metabolic fuel.The performance data reported here are consistent with a previously established biochemical framework. The teleost heart has the capability of utilizing exogenous fatty acid as a metabolic fuel and this substrate may be able to support the contractile process independently. In contrast, fatty acid metabolism in the elasmobranch heart is poorly developed and appears to be more dependent upon the catabolism of blood borne ketone bodies.     

Oxygen consumption and force development in turtle and trout cardiac muscle during acidosis and high extracellular potassium

Relative to species such as rainbow trout, freshwater turtle shows a high tolerance to challenges involving acidosis and increases in extracellular K+. Therefore, the effects of acidosis or high K+ on twitch force and oxygen consumption were examined in ventricular ring preparations from these two species. The oxygen consumption associated with force development was estimated by net oxygen consumption (oxygen consumption during twitch force development minus that during rest). For turtle, elevation of CO2 from 2% (pH 7.7) to 12% (pH 6.9) in the gas equilibrating the muscle bath decreased twitch force by 20% without any effects on oxygen consumption. Decreasing pH from 7.7 to 6.9 with 22 mM lactic acid had similar effects. For trout, CO2-induced acidosis decreased twitch force by approximately 60%. Furthermore, force development became energetically less efficient as it fell disproportionately more than net oxygen consumption. This was not observed for lactic acidosis. For trout but not for turtle, acidosis resulted in an increase in oxygen consumption during rest. An increase in extracellular K+ from 2.5 mM to 10 mM depressed force and oxygen consumption proportionately for both species. Adrenaline (10 microM) increased twitch force for both species and oxygen consumption for trout; it attenuated the effects of high extracellular K+. Neither adrenaline nor high K+ influenced the ratio of force to net oxygen consumption. As opposed to high extracellular K+, acidosis appears to increase the energetic cost of contractility, particularly for the trout heart.     

Inotropic effect of chlorpromazine on the frog atrium

The chlorpromazine, a calmodulin inhibitor, has been studied for its action on the contraction force and calcium current of the frog atrium fibres. Chlorpromazine (10(-5) mol/l) was observed to induce maximal increase of the contraction force that 30 min after the agent action amounted to (47.3 + 9.3)% of control. The high concentration of chlorpromazine (10(-4) mol/l) produced irreversible decrease in the contraction force. Chlorpromazine (10(-5) mol/l) increased the calcium current by (27.5 +/- 4.8)%. It is supposed that chlorpromazine increases contraction force and calcium current through the inhibition of calmodulin-dependent phosphodiesterase activity.     

Beneficial effect of fluorocarbon emulsion media on the function of neuromuscular preparations in vitro

The effects of liquid fluorocarbons as bathing media were determined by use of in vitro neuromuscular preparations. Rat hemidiaphragms were bathed in either oxygenated fluorocarbon (FC) emulsion or standard oxygenated Krebs solution. Contractile force in response to simple supramaximal nerve stimuli as well as to high frequency stimulation was greater, while twitch:tetanus ratio was smaller in FC emulsion. With such medium, post-tetanic potentiation of contraction was also more consistently observed. Indirectly stimulated diaphragms survived longer in FC emulsion. After cessation of oxygenation, oxygen tension (ρO(2)) of the medium declined more rapidly with Krebs than with FC emulsion; ρO(2) directly correlated with force of contraction. Similarly, in the chick biventer cervicis preparation, FC emulsion enhanced nerve-stimulated force of contraction; returning the preparation to standard Krebs solution reversed this phenomenon. Dose-resonse curves of muscle contraction in response to acetycholine and KCl administration were shifted upward during FC emulsion superfusion. Frequency of miniature endplate potentials was lower in FC emulsion than that observed in Krebs solution, measured from the same cell of the rat diaphragm. Resting membrane potentials were also greater in muscle cells sampled from FC emulsion-bathed preparations. These data suggest that FC emulsion is superior to standard Krebs solution as a bathing medium for in vitro neuromuscular preparations by virtue of the high solubility of oxygen in it.