Studies with a reconstituted muscle glycolytic system. The anaerobic glycolytic response to simulated tetanic contraction.
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ABSTRACT:
SUBMITTER: Scopes RK
PROVIDER: S-EPMC1166181 | biostudies-other | 1974 Jan
REPOSITORIES: biostudies-other
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Project description:A mixture of purified muscle glycolytic enzymes was reconstituted and the mixture shown to behave in a fashion analogous to that occurring in vivo. Glycolysis leads to ATP production in muscle and results in the phosphorylation of creatine. The extent of this phosphorylation by anaerobic glycolysis was shown to depend to a small extent on the relative proportions of available P(i) and creatine initially, but more importantly on the first step in glycolysis, in this case the enzyme phosphorylase. With less than 0.1% of the phosphorylase in the a form, only about one-third of the creatine was phosphorylated in 30min, whereas with 4% or more of phosphorylase a, 90% of the creatine was phosphorylated within this time. Inclusion of an adenosine triphosphatase decreased the steady-state concentration of phosphocreatine in the system. Calculations of the theoretical concentrations of ADP and AMP showed that phosphorylase b was almost inactive even in the presence of 9mum-AMP, because of ATP inhibition. With phosphorylase a present, glycolysis was able to continue at least until the calculated concentration of MgADP(-) was only 7mum, and AMP in the sub-mumolar range. The relation of these values to measured concentrations of nucleotides and to phosphorylase a percentages in intact muscle is discussed.
| S-EPMC1177800 | biostudies-other
Project description:The reconstituted glycolytic system described previously (Scopes, 1973) was used to simulate post-mortem glycolytic metabolism in muscle. The effects of the following factors have been investigated: ATPase (adenosine triphosphatase) amount, AMP deaminase amount, percentage of the phosphorylase in the a form and the effect of diluting the glycolytic enzyme complex as a whole. It was confirmed that the rate of metabolism was solely dependent on the amount of ATPase present and that various concentrations of the glycolytic enzymes had no effect over a wide range encompassing the variation found in anatomically different muscles. The extent of metabolism, represented by the value of the ;ultimate' pH, depended markedly on the amount of phosphorylase in the a form; as little as 1% of the a form resulted in a considerably lower pH than in its absence. To a lesser extent the amount of AMP deaminase also affected the ultimate pH, but this was probably only significant for comparisons of genetically distinct muscles with widely differing amounts of AMP deaminase. The reconstituted system behaved almost identically with regard to post-mortem glycolytic metabolism compared with intact muscle tissue. It is concluded that the controlling effectors found with the reconstituted system apply to intact muscle also.
| S-EPMC1168213 | biostudies-other
Project description:1. Gated 31P-n.m.r. spectra were obtained from the ankle flexor muscles of the rat at various times after 3 s isometric tetanic contraction. This allowed the time course of changes in phosphocreatine (PCr), Pi and free ADP concentrations and intracellular pH to be monitored in skeletal muscle in vivo with 1 s time resolution. 2. ATP concentration did not change significantly, either during the recovery from a 3 s tetanus or during the overall protocol. 3. The calculated rate of recovery of ADP towards pre-stimulation levels was very rapid (t1/2 less than 5 s). The rate of Pi disappearance (t1/2 = 14 s) was more rapid than the rate of PCr synthesis (t1/2 = 24 s), resulting in a significant transient decrease in n.m.r.-visible PCr + Pi between 25 and 45 s after tetanic contraction. 4. The rates of PCr, Pi and ADP recovery are higher than those previously reported for recovery from steady-state exercise in humans or twitch isometric contraction in animals.
| S-EPMC1138549 | biostudies-other
Project description:The dynamic computer model of oxidative phosphorylation developed previously and successfully tested for large-scale changes in fluxes and metabolite concentrations was used to study the question of how the rate of ATP production by oxidative phosphorylation is adjusted to meet the energy demand during muscle contraction, which causes a great increase in ATP consumption in relation to the resting state. The changes in the respiration rate and ATP/ADP ratio after the onset of maximal work measured experimentally were compared with simulated changes in the respiration rate and ATP/ADP in several different cases, assuming direct activation of different steps by an external effector. On the basis of the computer simulations performed, it was possible to conclude which enzymes/metabolic blocks should be directly activated to cause the experimentally observable changes in fluxes and metabolite concentrations. The theoretical results obtained suggest that the parallel direct activation of actinomyosin-ATP-ase and oxidative phosphorylation by an external effector (for example calcium ions) is the main mechanism responsible for fitting of ATP production to ATP consumption, while the negative feedback via an increase in ADP concentration (decrease in ATP/ADP), which indirectly activates the ATP supply, plays only a minor role. Additionally, the conclusion is drawn that most of the oxidative phosphorylation steps should be directly activated in order to explain the observed changes in the respiration rate and ATP/ADP ratio (and also in other parameters) during muscle contraction. It is suggested that there should exist a universal external activator/regulatory mechanism which causes a parallel stimulation of different enzymes/processes. A possible nature of such an activator is shortly discussed.
| S-EPMC1219260 | biostudies-other
Project description:Time-resolved X-ray diffraction of isolated fast-twitch muscles of mice was used to show how structural changes in the myosin-containing thick filaments contribute to the regulation of muscle contraction, extending the previous focus on regulation by the actin-containing thin filaments. This study shows that muscle activation involves the following sequence of structural changes: thin filament activation, disruption of the helical array of myosin motors characteristic of resting muscle, release of myosin motor domains from the folded conformation on the filament backbone, and actin attachment. Physiological force generation in the 'twitch' response of skeletal muscle to single action potential stimulation is limited by incomplete activation of the thick filament and the rapid inactivation of both filaments. Muscle relaxation after repetitive stimulation is accompanied by a complete recovery of the folded motor conformation on the filament backbone but by incomplete reformation of the helical array, revealing a structural basis for post-tetanic potentiation in isolated muscles.
| S-EPMC8275128 | biostudies-literature
Project description:Spinal cord injury (SCI) causes severe bone loss and disrupts connections between higher centers in the central nervous system (CNS) and bone. Muscle contraction elicited by functional electrical stimulation (FES) partially protects against loss of bone but cellular and molecular events by which this occurs are unknown. Here, using a rat model, we characterized effects of 7 days of contraction-induced loading of tibia and fibula due to FES when begun 16 weeks after SCI. SCI reduced tibial and femoral BMD by 12-17% and promoted bone resorption, as indicated by increased serum CTX; SCI-related changes in CTX were reversed by FES. In cultures of bone marrow cell-derived cells, SCI increased the number of osteoclasts and mRNA levels of the several osteoclast differentiation markers; these changes were significantly reversed by FES. The number of osteoblasts was also reduced by SCI as was the ratio of OPG/RANKL mRNAs therein; the unfavorable change in OPG/RANKL ratio was partially reversed by FES. cDNA microarray analysis revealed that alterations in genes involved in signaling through Wnt, FSH/LH, PTH and calcineurin/NFAT pathways may be linked to the favorable action of FES on SCI-induced bone resorption. In particular, SCI increased levels of the Wnt inhibitors DKK1, sFRP2 and SOST in osteoblasts, These effects were completely or partially reversed by FES. Our results demonstrate an anti-bone resorptive activity of acute FES in bone loss after SCI and suggest potential underlying mechanisms, among them involving increased Wnt signaling to cause more favorable ratios of OPG and RANKL for the inhibition of osteoclastogenesis. The present study indicates that the effects of bone reloading on SCI- related bone remodeling occurred independently of the effects of higher CNS centers on bone. Implantation of the FES microstimulators was performed 14 weeks after SCI. The FES was begun during the 16th week following spinal cord transection. Stimulation was provided for 60 minutes on each training day and consisted of brief periods of contraction (2 seconds) at 40 Hz at 1.5 V with longer periods of rest (18 seconds). Animals received FES on 7 consecutive days; collection of blood and tissues occurred at day at after initiating FES, as described below. The SCI-Sham FES animals received the implant surgery and gastrocnemius ablation during the 14th week after the spinal cord transection, but did not have a stimulator unit inserted; samples were collected from these animals at week 17. To provide age-matched non-SCI controls, additional animals underwent a sham-SCI surgery identical to that for the SCI animals, except that the spinal cord was not transected. Tissues were collected from these animals at 12-14 weeks after surgery. Of note, at this age, animals were sexually mature and their growth minimal. To collect blood and tissues, animals were anesthetized by inhalation of isofluorane followed by removal of the soleus and plantaris muscles after careful dissection and collection of blood by ventricular puncture and aspiration. Animals were euthanized by aortic transaction and tibia and femur were removed as a single piece, leaving the knee joint intact, and placed in a-MEM for isolation of bone marrow cells. Muscles were weighed; weights are expressed after being normalized to body weight before SCI or sham-SCI surgeries to control for individual variations in size.
2012-06-27 | E-GEOD-30301 | biostudies-arrayexpress
Project description:Spinal cord injury (SCI) causes severe bone loss and disrupts connections between higher centers in the central nervous system (CNS) and bone. Muscle contraction elicited by functional electrical stimulation (FES) partially protects against loss of bone but cellular and molecular events by which this occurs are unknown. Here, using a rat model, we characterized effects of 7 days of contraction-induced loading of tibia and fibula due to FES when begun 16 weeks after SCI. SCI reduced tibial and femoral BMD by 12-17% and promoted bone resorption, as indicated by increased serum CTX; SCI-related changes in CTX were reversed by FES. In cultures of bone marrow cell-derived cells, SCI increased the number of osteoclasts and mRNA levels of the several osteoclast differentiation markers; these changes were significantly reversed by FES. The number of osteoblasts was also reduced by SCI as was the ratio of OPG/RANKL mRNAs therein; the unfavorable change in OPG/RANKL ratio was partially reversed by FES. cDNA microarray analysis revealed that alterations in genes involved in signaling through Wnt, FSH/LH, PTH and calcineurin/NFAT pathways may be linked to the favorable action of FES on SCI-induced bone resorption. In particular, SCI increased levels of the Wnt inhibitors DKK1, sFRP2 and SOST in osteoblasts, These effects were completely or partially reversed by FES. Our results demonstrate an anti-bone resorptive activity of acute FES in bone loss after SCI and suggest potential underlying mechanisms, among them involving increased Wnt signaling to cause more favorable ratios of OPG and RANKL for the inhibition of osteoclastogenesis. The present study indicates that the effects of bone reloading on SCI- related bone remodeling occurred independently of the effects of higher CNS centers on bone.
2012-06-28 | GSE30301 | GEO
Project description:All eukaryotes carry out glycolysis, interestingly, not all using the same enzymes. Anaerobic eukaryotes face the challenge of fewer molecules of ATP extracted per molecule of glucose due to their lack of a complete tricarboxylic acid cycle. This may have pressured anaerobic eukaryotes to acquire the more ATP-efficient alternative glycolytic enzymes, such as pyrophosphate-fructose 6-phosphate phosphotransferase and pyruvate orthophosphate dikinase, through lateral gene transfers from bacteria and other eukaryotes. Most studies of these enzymes in eukaryotes involve pathogenic anaerobes; Monocercomonoides, an oxymonad belonging to the eukaryotic supergroup Excavata, is a nonpathogenic anaerobe representing an evolutionarily and ecologically distinct sampling of an anaerobic glycolytic pathway. We sequenced cDNA encoding glycolytic enzymes from a previously established cDNA library of Monocercomonoides and analyzed the relationships of these enzymes to those from other organisms spanning the major groups of Eukaryota, Bacteria, and Archaea. We established that, firstly, Monocercomonoides possesses alternative versions of glycolytic enzymes: fructose-6-phosphate phosphotransferase, both pyruvate kinase and pyruvate orthophosphate dikinase, cofactor-independent phosphoglycerate mutase, and fructose-bisphosphate aldolase (class II, type B). Secondly, we found evidence for the monophyly of oxymonads, kinetoplastids, diplomonads, and parabasalids, the major representatives of the Excavata. We also found several prokaryote-to-eukaryote as well as eukaryote-to-eukaryote lateral gene transfers involving glycolytic enzymes from anaerobic eukaryotes, further suggesting that lateral gene transfer was an important factor in the evolution of this pathway for denizens of this environment.
| S-EPMC1694820 | biostudies-literature
Project description:Pulmonary vasoconstriction and increased vascular resistance are common features in pulmonary hypertension (PH). One of the contributing factors in the development of pulmonary vasoconstriction is increased pulmonary artery smooth muscle cell (PASMC) contraction. Here we report that CCN1, an extracellular matrix molecule, suppressed PASMC contraction in response to hypoxia. CCN1 (Cyr61), discovered in past decade, belongs to the Cyr61-CTGF-Nov (CCN) family. It carries a variety of cellular functions, including angiogenesis and cell adhesion, death, and proliferation. Hypoxia robustly upregulated the expression of CCN1 in the pulmonary vessels and lung parenchyma. Given that CCN1 is a secreted protein and functions in a paracine manner, we examined the potential effects of CCN1 on the adjacent smooth muscle cells. Interestingly, bioactive recombinant CCN1 significantly suppressed hypoxia-induced contraction in human PASMCs in vitro. Consistently, in the in vivo functional studies, administration of bioactive CCN1 protein significantly decreased right ventricular pressure in three different PH animal models. Mechanistically, protein kinase A-pathway inhibitors abolished the effects of CCN1 in suppressing PASMC contraction. Furthermore, CCN1-inhibited smooth muscle contraction was independent of the known vasodilators, such as nitric oxide. Taken together, our studies indicated a novel cellular function of CCN1, potentially regulating the pathogenesis of PH.
| S-EPMC4671746 | biostudies-other
Project description:Although Caenorhabditis elegans has been utilized extensively to study synapse formation and function, relatively little is known about synaptic plasticity in C. elegans. We show that a brief treatment with the cholinesterase inhibitor aldicarb induces a form of presynaptic potentiation whereby ACh release at neuromuscular junctions (NMJs) is doubled. Aldicarb-induced potentiation was eliminated by mutations that block processing of proneuropeptides, by mutations inactivating a single proneuropeptide (NLP-12), and by those inactivating an NLP-12 receptor (CKR-2). NLP-12 expression is limited to a single stretch-activated neuron, DVA. Analysis of a YFP-tagged NLP-12 suggests that aldicarb stimulates DVA secretion of NLP-12. Mutations disrupting the DVA mechanoreceptor (TRP-4) decreased aldicarb-induced NLP-12 secretion and blocked aldicarb-induced synaptic potentiation. Mutants lacking NLP-12 or CKR-2 have decreased locomotion rates. Collectively, these results suggest that NLP-12 mediates a mechanosensory feedback loop that couples muscle contraction to changes in presynaptic release, thereby providing a mechanism for proprioceptive control of locomotion.
| S-EPMC3134788 | biostudies-literature