Na+-K+-ATPase in rat skeletal muscle: muscle fiber-specific differences in exercise-induced changes in ion affinity and maximal activity

2009 ◽  
Vol 296 (1) ◽  
pp. R125-R132 ◽  
Author(s):  
Carsten Juel
Keyword(s):  
Skeletal Muscle ◽  
Atpase Activity ◽  
Muscle Fiber ◽  
Muscle Activity ◽  
Fiber Type ◽  
Treadmill Running ◽  
Vitro Activity ◽  
In Vitro Activity ◽  
Rat Skeletal Muscle

It is unclear whether muscle activity reduces or increases Na+-K+-ATPase maximal in vitro activity in rat skeletal muscle, and it is not known whether muscle activity changes the Na+-K+-ATPase ion affinity. The present study uses quantification of ATP hydrolysis to characterize muscle fiber type-specific changes in Na+-K+-ATPase activity in sarcolemmal membranes and in total membranes obtained from control rats and after 30 min of treadmill running. ATPase activity was measured at Na+ concentrations of 0–80 mM and K+ concentrations of 0–10 mM. Km and Vmax values were obtained from a Hill plot. Km for Na+ was higher (lower affinity) in total membranes of glycolytic muscle (extensor digitorum longus and white vastus lateralis), when compared with oxidative muscle (red gastrocnemius and soleus). Treadmill running induced a significant decrease in Km for Na+ in total membranes of glycolytic muscle, which abolished the fiber-type difference in Na+ affinity. Km for K+ (in the presence of Na+) was not influenced by running. Running only increased the maximal in vitro activity ( Vmax) in total membranes from soleus, whereas Vmax remained constant in the three other muscles tested. In conclusion, muscle activity induces fiber type-specific changes both in Na+ affinity and maximal in vitro activity of the Na+-K+-ATPase. The underlying mechanisms may involve translocation of subunits and increased association between PLM units and the αβ complex. The changes in Na+-K+-ATPase ion affinity are expected to influence muscle ion balance during muscle contraction.

AMP-activated protein kinase activity and glucose uptake in rat skeletal muscle

2001 ◽  
Vol 280 (5) ◽  
pp. E677-E684 ◽  
Author(s):  
Nicolas Musi ◽  
Tatsuya Hayashi ◽  
Nobuharu Fujii ◽  
Michael F. Hirshman ◽  
Lee A. Witters ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Protein Kinase ◽  
Glucose Uptake ◽  
Muscle Contractions ◽  
Treadmill Running ◽  
Dependent Manner ◽  
Rat Skeletal Muscle ◽  
Amp Activated Protein Kinase ◽  
Dose Dependent

The AMP-activated protein kinase (AMPK) has been hypothesized to mediate contraction and 5-aminoimidazole-4-carboxamide 1-β-d-ribonucleoside (AICAR)-induced increases in glucose uptake in skeletal muscle. The purpose of the current study was to determine whether treadmill exercise and isolated muscle contractions in rat skeletal muscle increase the activity of the AMPKα1 and AMPKα2 catalytic subunits in a dose-dependent manner and to evaluate the effects of the putative AMPK inhibitors adenine 9-β-d-arabinofuranoside (ara-A), 8-bromo-AMP, and iodotubercidin on AMPK activity and 3- O-methyl-d-glucose (3-MG) uptake. There were dose-dependent increases in AMPKα2 activity and 3-MG uptake in rat epitrochlearis muscles with treadmill running exercise but no effect of exercise on AMPKα1 activity. Tetanic contractions of isolated epitrochlearis muscles in vitro significantly increased the activity of both AMPK isoforms in a dose-dependent manner and at a similar rate compared with increases in 3-MG uptake. In isolated muscles, the putative AMPK inhibitors ara-A, 8-bromo-AMP, and iodotubercidin fully inhibited AICAR-stimulated AMPKα2 activity and 3-MG uptake but had little effect on AMPKα1 activity. In contrast, these compounds had absent or minimal effects on contraction-stimulated AMPKα1 and -α2 activity and 3-MG uptake. Although the AMPKα1 and -α2 isoforms are activated during tetanic muscle contractions in vitro, in fast-glycolytic fibers, the activation of AMPKα2-containing complexes may be more important in regulating exercise-mediated skeletal muscle metabolism in vivo. Development of new compounds will be required to study contraction regulation of AMPK by pharmacological inhibition.

scholarly journals Tissue-Engineered Skeletal Muscle Models to Study Muscle Function, Plasticity, and Disease

2021 ◽  
Vol 12 ◽  
Author(s):  
Alastair Khodabukus
Keyword(s):  
Skeletal Muscle ◽  
Animal Models ◽  
Muscle Fiber ◽  
Muscle Function ◽  
Fiber Type ◽  
Small Animal ◽  
Muscle Fiber Type ◽  
Small Animal Models ◽  
Muscle Models

Skeletal muscle possesses remarkable plasticity that permits functional adaptations to a wide range of signals such as motor input, exercise, and disease. Small animal models have been pivotal in elucidating the molecular mechanisms regulating skeletal muscle adaptation and plasticity. However, these small animal models fail to accurately model human muscle disease resulting in poor clinical success of therapies. Here, we review the potential of in vitro three-dimensional tissue-engineered skeletal muscle models to study muscle function, plasticity, and disease. First, we discuss the generation and function of in vitro skeletal muscle models. We then discuss the genetic, neural, and hormonal factors regulating skeletal muscle fiber-type in vivo and the ability of current in vitro models to study muscle fiber-type regulation. We also evaluate the potential of these systems to be utilized in a patient-specific manner to accurately model and gain novel insights into diseases such as Duchenne muscular dystrophy (DMD) and volumetric muscle loss. We conclude with a discussion on future developments required for tissue-engineered skeletal muscle models to become more mature, biomimetic, and widely utilized for studying muscle physiology, disease, and clinical use.

Carnitine delays rat skeletal muscle fatigue in vitro

1993 ◽  
Vol 75 (4) ◽  
pp. 1595-1600 ◽  
Author(s):  
E. P. Brass ◽  
A. M. Scarrow ◽  
L. J. Ruff ◽  
K. A. Masterson ◽  
E. Van Lunteren
Keyword(s):  
Skeletal Muscle ◽  
Soleus Muscle ◽  
Fiber Type ◽  
Type I ◽  
Glycogen Depletion ◽  
Rat Skeletal Muscle ◽  
Skeletal Muscle Function ◽  
Total Carnitine ◽  
Initial Force

Carnitine has been used to enhance human exercise performance. To test the hypothesis that carnitine can directly modify skeletal muscle function, fatigue of isolated rat skeletal muscle strips was studied in vitro. Carnitine (10 mM) did not modify the initial force of soleus contraction. The time over which force declined by 50% during repetitive electrical stimulation of the soleus muscle (fiber type I) was prolonged 25% in the presence of 10 mM carnitine. In contrast, carnitine had no effect on the fatigue of extensor digitorum longus muscle strips (fiber type II). The beneficial effect of carnitine on soleus muscle strips was not observed if the routine 30-min preincubation in the presence of carnitine was decreased to 5 min; it was associated with a five- to sixfold increase in muscle total carnitine content and a 50#x2013;150% increase in muscle long-chain acylcarnitine content. Carnitine did not consistently modify lactate accumulation or glycogen depletion during the fatigue protocol. Incubation with propionyl-L-carnitine resulted in a decreased initial force of contraction and a delay in reaching maximal contractile force. Thus, carnitine can directly improve the fatigue characteristics of muscles enriched in type I fibers.

Single fiber analyses of glycogen-related proteins reveal their differential association with glycogen in rat skeletal muscle

2012 ◽  
Vol 303 (11) ◽  
pp. C1146-C1155 ◽  
Author(s):  
Robyn M. Murphy ◽  
Hongyang Xu ◽  
Heidy Latchman ◽  
Noni T. Larkins ◽  
Paul R. Gooley ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Fiber Type ◽  
Glycogen Synthesis ◽  
Glycogen Metabolism ◽  
Muscle Physiology ◽  
Rat Skeletal Muscle ◽  
Muscle Glycogen Synthesis ◽  
Triton X ◽  
Fast Twitch

To understand how glycogen affects skeletal muscle physiology, we examined enzymes essential for muscle glycogen synthesis and degradation using single fibers from quiescent and stimulated rat skeletal muscle. Presenting a shift in paradigm, we show these proteins are differentially associated with glycogen granules. Protein diffusibility and/or abundance of glycogenin, glycogen branching enzyme (GBE), debranching enzyme (GDE), phosphorylase (GP), and synthase (GS) were examined in fibers isolated from rat fast-twitch extensor digitorum longus (EDL) and slow-twitch soleus (SOL) muscle. GDE and GP proteins were more abundant (∼10- to 100-fold) in fibers from EDL compared with SOL muscle. GS and glycogenin proteins were similar between muscles while GBE had an approximately fourfold greater abundance in SOL muscle. Mechanically skinned fibers exposed to physiological buffer for 10 min showed ∼70% total pools of GBE and GP were diffusible (nonbound), whereas GDE and GS were considerably less diffusible. Intense in vitro stimulation, sufficient to elicit a ∼50% decrease in intracellular glycogen, increased diffusibility of GDE, GP, and GS (∼15–60%) and decreased GBE diffusibility (∼20%). Amylase treatment, which breaks α-1,4 linkages of glycogen, indicated differential diffusibilities and hence glycogen associations of GDE and GS. Membrane solubilization (1% Triton-X-100) allowed a small additional amount of GDE and GS to diffuse from fibers, suggesting the majority of nonglycogen-associated GDE/GS is associated with myofibrillar/contractile network of muscle rather than membranes. Given differences in enzymes required for glycogen metabolism, the current findings suggest glycogen particles have fiber-type-dependent structures. The greater catabolic potential of glycogen breakdown in fast-twitch fibers may account for different contraction induced rates of glycogen utilization.

Exercise-induced increase in maximal in vitro Na-K-ATPase activity in human skeletal muscle

2013 ◽  
Vol 304 (12) ◽  
pp. R1161-R1165 ◽  
Author(s):  
Carsten Juel ◽  
Nikolai B. Nordsborg ◽  
Jens Bangsbo
Keyword(s):  
Skeletal Muscle ◽  
Atpase Activity ◽  
Muscle Activity ◽  
Human Skeletal Muscle ◽  
Vastus Lateralis ◽  
Acute Hypoxia ◽  
Maximal Velocity ◽  
Atpase Assay ◽  
Before And After

The present study investigated whether maximal in vitro Na-K-ATPase activity in human skeletal muscle is changed with exercise and whether it was altered by acute hypoxia. Needle biopsies from 14 subjects were obtained from vastus lateralis before and after 4 min of intense muscle activity. In addition, six subjects exercised also in hypoxia (12.5% oxygen). The Na-K-ATPase assay revealed a 19% increase ( P < 0.05) in maximal velocity ( Vmax) for Na+-dependent Na-K-ATPase activity after exercise and a tendency ( P < 0.1) toward a decrease in Km for Na+ (increased Na+ affinity) in both normoxia and hypoxia. In contrast, the in vitro Na-K-ATPase activity determined with the 3- O-MFPase technique was 11–32% lower after exercise in normoxia ( P < 0.05) and hypoxia ( P < 0.1). Based on the different results obtained with the Na-K-ATPase assay and the 3- O-MFPase technique, it was suggested that the 3- O-MFPase method is insensitive to changes in Na-K-ATPase activity. To test this possibility, changes in Na-K-ATPase activity was induced by protein kinase C activation. The changes quantified with the Na-K-ATPase assay could not be detected with the 3- O-MFPase method. In addition, purines stimulated Na-K-ATPase activity in rat muscle membranes; these changes could not be detected with the 3- O-MFPase method. Therefore, the 3- O-MFPase technique is not sensitive to changes in Na+ sensitivity, and the method is not suited to detecting changes in Na-K-ATPase activity with exercise. In conclusion, muscle activity in humans induces an increased in vitro Na+-dependent Na-K-ATPase activity, which contributes to the upregulation of the Na-K-ATPase in association with exercise both in normoxia and hypoxia.

In Vitro Activity of Phytocannabinoids from High Potency Cannabis sativa

Planta Medica ◽  
2012 ◽  
Vol 78 (05) ◽  
Author(s):  
A Husni ◽  
S Ross ◽  
O Dale ◽  
C Gemelli ◽  
G Ma ◽  
...  
Keyword(s):  
Cannabis Sativa ◽  
Vitro Activity ◽  
In Vitro Activity ◽  
High Potency
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