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Albadrani H, Ammar T, Bader M, Renaud JM. Angiotensin 1-7 prevents the excessive force loss resulting from 14- and 28-day denervation in mouse EDL and soleus muscle. J Gen Physiol 2021; 153:212748. [PMID: 34739541 PMCID: PMC8576869 DOI: 10.1085/jgp.201912556] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2019] [Revised: 06/30/2021] [Accepted: 08/11/2021] [Indexed: 11/20/2022] Open
Abstract
Denervation leads to muscle atrophy, which is described as muscle mass and force loss, the latter exceeding expectation from mass loss. The objective of this study was to determine the efficiency of angiotensin (Ang) 1–7 at reducing muscle atrophy in mouse extensor digitorum longus (EDL) and soleus following 14- and 28-d denervation periods. Some denervated mice were treated with Ang 1–7 or diminazene aceturate (DIZE), an ACE2 activator, to increase Ang 1–7 levels. Ang 1–7/DIZE treatment had little effect on muscle mass loss and fiber cross-sectional area reduction. Ang 1–7 and DIZE fully prevented the loss of tetanic force normalized to cross-sectional area and accentuated the increase in twitch force in denervated muscle. However, they did not prevent the shift of the force–frequency relationship toward lower stimulation frequencies. The Ang 1–7/DIZE effects on twitch and tetanic force were completely blocked by A779, a MasR antagonist, and were not observed in MasR−/− muscles. Ang 1–7 reduced the extent of membrane depolarization, fully prevented the loss of membrane excitability, and maintained the action potential overshoot in denervated muscles. Ang 1–7 had no effect on the changes in α-actin, myosin, or MuRF-1, atrogin-1 protein content or the content of total or phosphorylated Akt, S6, and 4EPB. This is the first study that provides evidence that Ang 1–7 maintains normal muscle function in terms of maximum force and membrane excitability during 14- and 28-d periods after denervation.
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Affiliation(s)
- Hind Albadrani
- University of Ottawa, Department of Cellular and Molecular Medicine, Ottawa, Ontario, Canada.,Majmaah University, Department of Medical Laboratory Sciences, Al Majma'ah, Saudi Arabia
| | - T Ammar
- University of Ottawa, Department of Cellular and Molecular Medicine, Ottawa, Ontario, Canada
| | - Michael Bader
- Max-Delbrück Center for Molecular Medicine, Berlin-Buch, Germany.,University of Lübeck, Institute for Biology, Lübeck, Germany.,Charité University Medicine, Berlin, Germany.,German Center for Cardiovascular Research, Berlin, Germany
| | - Jean-Marc Renaud
- University of Ottawa, Department of Cellular and Molecular Medicine, Ottawa, Ontario, Canada
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Ehmsen JT, Höke A. Cellular and molecular features of neurogenic skeletal muscle atrophy. Exp Neurol 2020; 331:113379. [PMID: 32533969 DOI: 10.1016/j.expneurol.2020.113379] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2019] [Revised: 05/26/2020] [Accepted: 06/08/2020] [Indexed: 12/28/2022]
Abstract
Neurogenic atrophy refers to the loss of muscle mass and function that results directly from injury or disease of the peripheral nervous system. Individuals with neurogenic atrophy may experience reduced functional status and quality of life and, in some circumstances, reduced survival. Distinct pathological findings on muscle histology can aid in diagnosis of a neurogenic cause for muscle dysfunction, and provide indicators for the chronicity of denervation. Denervation induces pleiotypic responses in skeletal muscle, and the molecular mechanisms underlying neurogenic muscle atrophy appear to share common features with other causes of muscle atrophy, including activation of FOXO transcription factors and corresponding induction of ubiquitin-proteasomal and lysosomal degradation. In this review, we provide an overview of histologic features of neurogenic atrophy and a summary of current understanding of underlying mechanisms.
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Affiliation(s)
- Jeffrey T Ehmsen
- Department of Neurology, Neuromuscular Division, Johns Hopkins School of Medicine, Baltimore, MD 21205, USA
| | - Ahmet Höke
- Department of Neurology, Neuromuscular Division, Johns Hopkins School of Medicine, Baltimore, MD 21205, USA.
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Witt A, Kristensen R, Fuglsang-Frederiksen A, Pedersen T, Finnerup N, Kasch H, Tankisi H. Muscle velocity recovery cycles in neurogenic muscles. Clin Neurophysiol 2019; 130:1520-1527. [DOI: 10.1016/j.clinph.2019.05.030] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2019] [Revised: 04/17/2019] [Accepted: 05/19/2019] [Indexed: 12/01/2022]
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Pond A, Marcante A, Zanato R, Martino L, Stramare R, Vindigni V, Zampieri S, Hofer C, Kern H, Masiero S, Piccione F. History, Mechanisms and Clinical Value of Fibrillation Analyses in Muscle Denervation and Reinnervation by Single Fiber Electromyography and Dynamic Echomyography. Eur J Transl Myol 2014; 24:3297. [PMID: 26913128 PMCID: PMC4749004 DOI: 10.4081/ejtm.2014.3297] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
This work reviews history, current clinical relevance and future of fibrillation, a functional marker of skeletal muscle denervated fibers. Fibrillations, i.e., spontaneous contraction, in denervated muscle were first described during the nineteenth century. It is known that alterations in membrane potential are responsible for the phenomenon and that they are related to changes in electrophysiological factors, cellular metabolism, cell turnover and gene expression. They are known to inhibit muscle atrophy to some degree and are used to diagnose neural injury and reinnervation that are occurring in patients. Electromyography (EMG) is useful in determining progress, prognosis and efficacy of therapeutic interventions and their eventual change. For patients with peripheral nerve injury, and thus without the option of volitional contractions, electrical muscle stimulation may be helpful in preserving the contractility and extensibility of denervated muscle tissue and in retarding/counteracting muscle atrophy. It is obvious from the paucity of recent literature that research in this area has declined over the years. This is likely a consequence of the decrease in funding available for research and the fact that the fibrillations do not appear to cause serious health issues. Nonetheless, further exploration of them as diagnostic tools in long-term denervation is merited, in particular if Single Fiber EMG (SFEMG) is combined with Dynamic Echomyography (DyEM), an Ultra Sound muscle approach we recently designed and developed to explore denervated and reinnervating muscles.
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Affiliation(s)
- Amber Pond
- Anatomy Department, Southern Illinois University School of Medicine, Carbondale, IL USA
| | - Andrea Marcante
- CIR-Myo, Rehabilitation and Physical Medicine Unit, Department of Neurosciences, University of Padova, Italy
| | - Riccardo Zanato
- CIR-Myo, Radiology, Department of Medicine, University of Padova, Italy
| | - Leonora Martino
- CIR-Myo, Radiology, Department of Medicine, University of Padova, Italy
| | - Roberto Stramare
- CIR-Myo, Radiology, Department of Medicine, University of Padova, Italy
| | - Vincenzo Vindigni
- CIR-Myo, Plastic Surgery, Department of Neuroscience, University of Padova, Italy
| | | | - Christian Hofer
- Ludwig Boltzmann Institute of Electrical Stimulation and Physical Rehabilitation, Vienna, Austria
| | | | - Stefano Masiero
- CIR-Myo, Rehabilitation and Physical Medicine Unit, Department of Neurosciences, University of Padova, Italy
| | - Francesco Piccione
- Clinical Neurophysiology, San Camillo Hospital I.R.C.C.S., Venezia-Lido, Italy
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Payne AM, Jimenez-Moreno R, Wang ZM, Messi ML, Delbono O. Role of Ca2+, membrane excitability, and Ca2+ stores in failing muscle contraction with aging. Exp Gerontol 2008; 44:261-73. [PMID: 18948183 DOI: 10.1016/j.exger.2008.09.013] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2008] [Revised: 09/18/2008] [Accepted: 09/21/2008] [Indexed: 10/21/2022]
Abstract
Excitation-contraction (EC) coupling in a population of skeletal muscle fibers of aged mice becomes dependent on the presence of external Ca(2+) ions (Payne, A.M., Zheng, Z., Gonzalez, E., Wang, Z.M., Messi, M.L., Delbono, O., 2004b. External Ca(2+)-dependent excitation - contraction coupling in a population of aging mouse skeletal muscle fibers. J. Physiol. 560, 137-155.). However, the mechanism(s) underlying this process remain unknown. In this work, we examined the role of (1) extracellular Ca(2+); (2) voltage-induced influx of external Ca(2+) ions; (3) sarcoplasmic reticulum (SR) Ca(2+) depletion during repeated contractions; (4) store-operated Ca(2+) entry (SOCE); (5) SR ultrastructure; (6) SR subdomain localization of the ryanodine receptor; and (7) sarcolemmal excitability in muscle force decline with aging. These experiments show that external Ca(2+), but not Ca(2+) influx, is needed to maintain force upon repetitive fiber electrical stimulation. Decline in fiber force is associated with depressed SR Ca(2+) release. SR Ca(2+) depletion, SOCE, and the putative segregated Ca(2+) release store do not play a significant role in external Ca(2+)-dependent contraction. More importantly, a significant number of action potentials fail in senescent mouse muscle fibers subjected to a stimulation frequency. These results indicate that failure to generate action potentials accounts for decreased intracellular Ca(2+) mobilization and tetanic force in aging muscle exposed to a Ca(2+)-free medium.
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Affiliation(s)
- Anthony Michael Payne
- Department of Physiology and Pharmacology, Wake Forest University School of Medicine, Winston-Salem, NC 27157, USA
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Kotsias BA, Venosa RA. Sodium influx during action potential in innervated and denervated rat skeletal muscles. Muscle Nerve 2001; 24:1026-33. [PMID: 11439377 DOI: 10.1002/mus.1106] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Resting Na(+) influx (J(i)(Na)) was measured in innervated and denervated (1-6 days) rat extensor digitorum longus muscle in the absence and presence of 2 micromol/L tetrodotoxin (TTX). The mean value of Na(+) permeability (P(Na)) in innervated muscles was 49.6 +/- 2.6 pm.s(-1). At the second day postdenervation, it decreased by about 45%. This was followed, between the second and fourth days, by a sharp rise, which by the sixth day reached a steady value approximately 2.5 times greater than that of innervated muscles. This, most likely, generated the 30% increase in internal [Na(+)] concentration ([Na(+)](I)) observed at this time. Tetrodotoxin reduced P(Na) of both innervated and denervated muscles by about 25%. In 6-day denervated muscles, virtually all the TTX effect on P(Na) represents the blockage of TTX-resistant Na(+) channels. Denervation produced a depolarization of about 20 mV by the sixth day. The extra J(i)(Na) per action potential (AP) decreased monotonically with time after denervation from 20.0 +/- 3.8 in innervated to 11.1 +/- 1.0 nmol.g(-1).AP(-1) in 6-day denervated muscles. The overshoot of the AP decreased from 15 +/- 1 in innervated to 7 +/- 1 mV in 6-day denervated muscles. Likewise, the maximum rate of rise (+dV/dt), an expression of the inward Na(+) current, fell from 305 +/- 14 in innervated to 188 +/- 18 V.s(-1) in 6-day denervated muscles. The estimated 6-day denervated/innervated ratio of peak Na(+) conductance (g(Na)) was 0.67. The changes in AP parameters promoted by denervation were substantially reduced when both innervated and denervated fibers were hyperpolarized to -90 mV. These results suggest that the depolarization, mainly due to the increase in P(Na) /P(K) ratio, increases Na(+) inactivation and consequently reduces peak g(Na), in spite of the absolute increment in resting TTX-sensitive P(Na). This, in addition to the moderate reduction in the inward driving force on Na(+), decreases the inward Na(+) current and the extra J(i)(Na) per AP.
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Affiliation(s)
- B A Kotsias
- Instituto de Investigaciones Médicas A. Lanari, Universidad de Buenos Aires and Centro de Investigaciones Cardiovasculares, Argentina Universidad de La Plata, La Plata, Argentina.
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Matar W, Lunde JA, Jasmin BJ, Renaud JM. Denervation enhances the physiological effects of the K(ATP) channel during fatigue in EDL and soleus muscle. Am J Physiol Regul Integr Comp Physiol 2001; 281:R56-65. [PMID: 11404279 DOI: 10.1152/ajpregu.2001.281.1.r56] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The objective was to determine whether denervation reduces or enhances the physiological effects of the K(ATP) channel during fatigue in mouse extensor digitorum longus (EDL) and soleus muscle. For this, we measured the effects of 100 microM of pinacidil, a channel opener, and of 10 microM of glibenclamide, a channel blocker, in denervated muscles and compared the data to those observed in innervated muscles from the study of Matar et al. (Matar W, Nosek TM, Wong D, and Renaud JM. Pinacidil suppresses contractility and preserves energy but glibenclamide has no effect during fatigue in skeletal muscle. Am J Physiol Cell Physiol 278: C404-C416, 2000). Pinacidil increased the (86)Rb(+) fractional loss during fatigue, and this effect was 2.6- to 3.4-fold greater in denervated than innervated muscle. Pinacidil also increased the rate of fatigue; for EDL the effect was 2.5-fold greater in denervated than innervated muscle, whereas for soleus the difference was 8.6-fold. A major effect of glibenclamide was an increase in resting tension during fatigue, which was for the EDL and soleus muscle 2.7- and 1.9-fold greater, respectively, in denervated than innervated muscle. A second major effect of glibenclamide was a reduced capacity to recover force after fatigue, an effect observed only in denervated muscle. We therefore suggest that the physiological effects of the K(ATP) channel are enhanced after denervation.
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Affiliation(s)
- W Matar
- Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, Ontario, Canada K1H 8M5
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Abstract
The extracellularly recorded configuration of a single muscle fiber discharge is generally appreciated to be triphasic with an initially positive deflection. However, careful attention to waveform appearance during the electrodiagnostic medicine examination reveals that both innervated and denervated muscle waveforms may display a pantheon of configurations. Further, despite the fact that innervated and denervated single muscle fiber discharges arise from distinctly different intracellular action potential (IAP) configurations, their extracellularly recorded waveforms can appear quite similar, leading to potential misidentification and, hence, the possibility of an erroneous diagnostic conclusion. The least appreciated, but nevertheless critical, aspect of explanations for muscle waveform configurations is the relationship between the muscle fiber and recording electrode. Additionally, it is important to appreciate both the near-field and far-field aspects of single fiber and compound muscle action potentials. In this review, the leading/trailing dipole model is used to explain muscle waveform configurations in both innervated and denervated tissues.
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Affiliation(s)
- D Dumitru
- Department of Rehabilitation Medicine, University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, San Antonio, Texas 78229-3900, USA.
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Escobar AL, Schinder AF, Biali FI, Nicola LC, Uchitel OD. Potassium channels from normal and denervated mouse skeletal muscle fibers. Muscle Nerve 1993; 16:579-86. [PMID: 8502254 DOI: 10.1002/mus.880160602] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The properties of singles K+ channels in normal and denervated muscles were compared using the "patch-clamp" technique. Single channels were recorded from vesicles obtained by stretching bundles of normal and denervated extensor digitorium longus (EDL) muscles. The most frequently observed channel in normal muscles was a high conductance (266 pS) Ca++ activated K+ channel. Although channel density, as estimated by patch recording, showed a significant decrease in denervated muscles, no differences were found in conductance and gating properties. Another voltage-dependent K+ channel (81 pS) was only recorded from normal muscles, but never from denervated ones. In addition, a 35 pS conductance was recorded from both normal and denervated fibers. This channel displayed neither voltage dependence nor sensitivity to tetraethylammonium (TEA). In contrast, another TEA-insensitive (16 pS) channel was recorded only from denervated muscles. We conclude that denervation induces significant changes in the distribution and expression of K+ channels in mammalian skeletal muscles.
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Affiliation(s)
- A L Escobar
- Instituto de Biología Celular, Facultad de Medicina, Universidad de Buenos Aires, Argentina
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Delbono O. Calcium current activation and charge movement in denervated mammalian skeletal muscle fibres. J Physiol 1992; 451:187-203. [PMID: 1328616 PMCID: PMC1176157 DOI: 10.1113/jphysiol.1992.sp019160] [Citation(s) in RCA: 49] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
1. Calcium current (ICa) activation was studied in denervated extensor digitorum longus muscle fibres of the rat. Denervation was performed by surgically removing 6-8 mm of the sciatic nerve at the sciatic notch. Controls were normal fibres from non-operated rats. Electrical recordings were carried out using the double Vaseline-gap technique. 2. Current-voltage (I-V) curves showed that the ICa amplitude increased during the first 4-6 days after denervation and subsequently decreased during the second week. Between days 4 and 6 after denervation, the peak ICa amplitude (at 0 mV) was -5.9 +/- 0.5 microA/microF (mean +/- S.E.M.) as compared with -4.8 +/- 0.3 microA/microF in normal fibres. Between days 14 and 15 after denervation, the ICa amplitude was -2.9 +/- 0.4 microA/microF. 3. The time constant of ICa activation (tau a) was significantly increased by denervation. At 0 mV, tau a in normal fibres was 44.8 +/- 1.4 ms. Between 4 and 6 days after denervation tau a was 58.1 +/- 4.8 ms, and between 14 and 15 days after denervation, 55.8 +/- 3.8 ms. 4. The time constant of deactivation (tau d) decreased after denervation. At -10 mV, the tau d in normal fibres was 103.4 +/- 14 ms. The value decreased to 74.5 +/- 8.6 and 74.0 +/- 17 ms between days 4 and 6 and days 14 and 15 of denervation respectively. 5. Charge movement (Qon) was reduced progressively without major changes in the steepness (k) and position on the voltage axis of the Qon-Vm relationship. The fitted parameters under control were Qmax = 15.4 nC/microF, mid-point potential Vq1/2 = -25.2 mV and k = 11.9 mV. Between days 14 and 15 of denervation, the values for Qmax, Vq1/2 and k were 6.7 nC/microF, -36.8 mV and 11.3 mV respectively. 6. Calcium permeability (PCa) in normal and denervated fibres at stages during denervation was calculated according to the Hodgkin-Huxley model. At 0 mV PCa was 1.24 x 10(-5) cm/s in normal fibres, and 7.43 x 10(-6) cm/s after 2 weeks of denervation. 7. The m infinity-Vm relationship was shifted to more positive potentials after denervation without significant changes in the steepness factor k. The V1/2 value in normal fibres was -4.4 mV, and 5.8 mV after two weeks of denervation. 8. The ICa sensitivity to nifedipine was not modified in the different groups of denervated fibres studied. With 10 microM-nifedipine, the 1-(ICa in nifedipine/ICa control) relationships were 0.74 +/- 0.03 in normal fibres and 0.76 +/- 0.12, 14 days after denervation.
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Affiliation(s)
- O Delbono
- Department of Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, TX 77030
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Delbono O, Kotsias BA. Calcium action potentials in innervated and denervated rat muscle fibres. Pflugers Arch 1991; 418:284-91. [PMID: 1649994 DOI: 10.1007/bf00370528] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
We studied the generation of calcium action potentials (Ca APs) in innervated and denervated fibres of the extensor digitorum longus of the rat in a tetraethylammonium (TEA) sulphate solution plus 3-4 diaminopiridine (3-4 DAP). The main results are the following: (1) more than 90% of the innervated fibres were capable of developing well-sustained Ca APs that were blocked by Cd or nifedipine; (2) the incidence of Ca APs obtained from the denervated fibres was substantially lower than in the control preparations; (3) no relation was found between the appearance of Ca APs in the denervated fibres and the resting membrane potential (Vm), stimulus duration (500-2000 ms) or holding potential (-80, -100 mV); (4) The percentage of denervated fibres that exhibited Ca APs was increased significantly with the following procedures. First, by raising the external Ca concentration to 14 mM; second, by depleting the intracellular K concentration by overnight exposure of the muscles to a free K-Cs solution; (c) and third, by incubating the muscles in 500 nM apamin, a venom that inhibits the K conductance activated by Ca. Several factors may be involved in the lower incidence of Ca APs obtained in denervated fibres: (1) a diminished Ca current due to a reduction in the driving force as a result of an increment in the intracellular Ca concentration; (2) a persistence of a shunting K conductance that is not inhibited by TEA and 3-4 DAP; (3) a shift in the voltage dependence of the activation and inactivation parameters of the Ca current or the appearance of a new type of Ca channel with a different kinetics.
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Affiliation(s)
- O Delbono
- Instituto de Investigaciones Médicas A. Lanari, UBA, Buenos Aires, Argentina
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Venosa RA. Hypo-osmotic stimulation of active Na+ transport in frog muscle: apparent upregulation of Na+ pumps. J Membr Biol 1991; 120:97-104. [PMID: 2072389 DOI: 10.1007/bf01872392] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
The purpose of this work was to determine if hypotonicity, in addition to the stimulation of active Na+ transport (Venosa, R.A., 1978, Biochim. Biophys. Acta 510:378-383), promoted changes in (i) active K+ influx, (ii) passive Na+ and K+ fluxes, and (iii) the number of 3H-ouabain binding sites. The results indicate that a reduction of external osmotic pressure (pi) to one-half of its normal value (pi = 0.5) produced the following effects: (i) an increase in active K+ influx on the order of 160%, (ii) a 20% reduction in Na+ influx and K+ permeability (PK), and (iii) a 40% increase in the apparent density of ouabain binding sites. These data suggest that the hypotonic stimulation of the Na+ pump is not caused by an increased leak of either Na+ (inward) or K+ (outward). It is unlikely that the stimulation of active Na+ extrusion and the rise in the apparent number of pump sites produced by hypotonicity were due to a reduction of the intracellular ionic strength. It appears that, at least in part, the stimulation of active Na+ transport takes place whenever muscles are transferred from one medium to another of lower tonicity even if neither one was hypotonic (for instance pi = 2 to pi = 1 transfer). Comparison of the present results with those previously reported indicate that in addition to the number of pump sites, the cycling rate of the pump is increased by hypotonicity. Active Na+ and K+ fluxes were not significantly altered by hypertonicity (pi = 2).
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Affiliation(s)
- R A Venosa
- Cátedra de Fisiología con Biof157isica, Facultad de Ciencias Médicas, Universidad Nacional de La Plata, Argentina
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Hundal HS, Babij P, Watt PW, Ward MR, Rennie MJ. Glutamine transport and metabolism in denervated rat skeletal muscle. THE AMERICAN JOURNAL OF PHYSIOLOGY 1990; 259:E148-54. [PMID: 2382709 DOI: 10.1152/ajpendo.1990.259.2.e148] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Rat skeletal muscle glutamine fell by 40% from 4.18 to 2.5 mumols/g wet weight (P less than 0.01) after 4 days of denervation. Over the same period net glutamine efflux from denervated hindlimbs [i.e., arteriovenous (a-v) concentration differences x blood flow] increased 3.5-fold (from -6.72 +/- 1.73 to -26 +/- 4.81 nmol.min-1.g-1, P less than 0.001). Gastrocnemius glutamine synthetase activity fell 48% after denervation (from 475 +/- 81 to 248 +/- 39 nmol.min-1.g-1, P less than 0.001), but glutaminase activity was not significantly altered (17 nmol.min-1.g-1). The maximal activity (Vmax) of the unidirectional Na(+)-dependent glutamine transporter (system Nm) was depressed by 45% from 1,020 +/- 104 to 571 +/- 9 nmol.min-1.g-1 (P less than 0.01), but the concentration at which transport was half maximal (Km) was not significantly altered (control 8.1 +/- 0.6 mM; denervated 6.52 +/- 0.12). Hindlimb denervation resulted in an increase of intramuscular Na+ by 17% and a fall of K+ by 12%, and the resting membrane potential in isolated muscles decreased from -75 +/- 10 to -59.5 +/- 5.5 mV. Membrane potential of perfused denervated muscle, isolated after acute addition of the Na+ channel blocker tetrodotoxin (TTX, 3 microM), repolarized to -66.4 +/- 3.2 mV. In perfused denervated preparations TTX caused an acute recovery of Vmax of unidirectional glutamine transport to 848 +/- 75 nmol.min-1.g-1; Km was unaffected.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- H S Hundal
- Department of Anatomy and Physiology, University of Dundee, United Kingdom
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