Molecular architecture of Ca2+ signaling control in muscle and heart cells

Ca²⁺ signaling in skeletal and cardiac muscles is a bi-directional process that involves cross-talk between signaling molecules in the sarcolemmal membrane and Ca²⁺ release machinery in the intracellular organelles. Maintenance of a junctional membrane structure between the sarcolemmal membrane and the sarcoplasmic reticulum (SR) provides a framework for the conversion of action potential arrived at the sarcolemma into release of Ca²⁺ from the SR, leading to activation of a variety of physiological processes. Activity-dependent changes in Ca²⁺ storage inside the SR provides a retrograde signal for the activation of store-operated Ca²⁺ channel (SOC) on the sarcolemmal membrane, which plays important roles in the maintenance of Ca²⁺ homeostasis in physiology and pathophysiology. Research progress during the last 30 years had advanced our understanding of the cellular and molecular mechanisms for the control of Ca²⁺ signaling in muscle and cardiovascular physiology. Here we summarize the functions of three key molecules that are located in the junctional membrane complex of skeletal and cardiac muscle cells: junctophilin as a “glue” that physiologically links the SR membrane to the sarcolemmal membrane for formation of the junctional membrane framework, mitsugumin29 as a muscle-specific synaptophysin family protein that contributes to maintain the coordinated Ca²⁺ signaling in skeletal muscle, and TRIC as a novel cation-selective channel located on the SR membrane that provides counter-ion current during the rapid process of Ca²⁺ release from the SR.     

Localization of calcium in skeletal and cardiac muscle

Summary The requirement of calcium (Ca²⁺) in the excitation-contraction coupling of both skeletal and cardiac muscle is well established. However, the exact location of the intracellular storage sites of Ca²⁺ is not firmly established. We report here on the ultrastructural distribution of Ca²⁺ in white and red skeletal muscle and in cardiac muscle of the rat using combined phosphate-pyroantimonate (PPA) and oxalate-pyroantimonate (OPA) procedures. The methods are based on (a) stabilization and/or trapping of Ca²⁺ during the primary fixation step in glutaraldehyde by potassium phosphate or oxalate; (b) subsequent wash-out of all non-trapped cations such as Na⁺ and Mg²⁺ in potassium phosphate or oxalate; (c) conversion of the complexed or trapped Ca²⁺ into an electron-dense calcium pyroantimonate salt in 100 m-thick tissue sections; and (d) wash-out of the excess potassium pyroantimonate at alkaline pH.With the OPA procedure, mitochondria of all muscle types showed little precipitate. The junctional sarcoplasmic reticulum was stongly reactive in relaxed white skeletal muscle, negative in contracted white fibres and negative in red skeletal and cardiac muscle, independent of the state of relaxation-contraction. Other organelles were essentially free of deposits.With the PPA method, the precipitate was almost exclusively confined to the sarcolemma and its T-tubular invaginations in cardiac and slow skeletal muscle, and was absent in fast skeletal muscle. Apart from occasional deposits in mitochondria, all other organelles were free of precipitate. The sarcolemma-associated deposits were clearly confined to the inner leaflet of the lipid bilayer. The amount of precipitate varied within the contraction cycle, relaxed cells possessing the highest density.Exposure of the tissue to La³⁺ resulted in the complete absence of sarcolemma-bound precipitate suggesting that the Ca²⁺ is exchangeable. Furthermore, these cytological data suggest a basic difference in Ca²⁺ storage between white skeletal muscle on the one hand, and red skeletal and cardiac muscle on the other.     

Troponin T isoforms alter the tolerance of transgenic mouse cardiac muscle to acidosis

Troponin T (TnT) is an essential protein in the Ca²⁺ regulatory system of striated of muscle. Three fiber type-specific TnT genes have evolved in higher vertebrates to encode cardiac, slow and fast skeletal muscle TnT isoforms. To understand the functional significance of TnT isoforms, we studied the effects of acidosis on the contractility of transgenic mouse cardiac muscle that expresses fast skeletal muscle TnT. Contractility analysis of intact cardiac muscle strips showed that while no differences were detected at physiological pH, the transgenic cardiac muscle had significantly greater decreases in +dF/dt_max at acidic pH than that of the wild-type control. Contractility of skinned cardiac muscles demonstrated that the presence of fast TnT resulted in significantly larger decreases in force and Ca²⁺ sensitivity at acidic pH than that of the wild-type control. The effect of TnT isoforms on the tolerance of muscle to acidosis may explain the higher tolerance of embryonic versus adult cardiac muscles. The results are consistent with the hypothesis that charge differences in TnT isoforms contribute to the contractility of muscle. The data further support a hypothesis that slow TnT is similar to the cardiac, but not fast, and TnT may contribute to the higher tolerance of slow muscles to stress conditions. Therefore, TnT isoform diversity may contribute to the compatibility of muscle thin filaments to cellular environments in different fiber types, during development and functional adaptation.     

Ca channels and skeletal muscle diseases

When observed under a microscope, skeletal muscle exhibits striations due to the highly organized arrangement of muscle proteins that interact with one another to induce muscle contraction. Muscle contraction requires transient increases in intracellular ‘Ca²⁺’ concentration. In this review, Ca²⁺ channels contributing to the functional integrity of intracellular Ca²⁺-release and extracellular Ca²⁺-entry during skeletal muscle contraction are reviewed in terms of their properties, newly emerging ancillary proteins to them, and their abnormalities related to human skeletal muscle diseases. Finally, the aim of this review is to show the big picture of the correlation among Ca²⁺ channels that participate in the Ca²⁺ homeostasis in skeletal muscle.     

Sodium Ions in the Electromechanical Coupling System of Myocardium and Skeletal Muscles of the Frog Rana temporaria

The role of the transsarcolemmal Na⁺ gradient in providing phasic contraction of myocardium and skeletal muscles of the common frog Rana temporaria was studied. It was shown that a decrease of the gradient by means of total or partial substitution of Na⁺ for Ch⁺ or Li⁺ produced a tissue-specific reduction of the isometric tension developed by the muscles as well as of the maximum rate of its development. The functional mechanisms of use of the Na⁺-gradient for intracellular mobilization of activator of the muscle contraction, Ca²⁺ ions, are considered, and the experimental evidences for significance of this gradient increase to provide intensification of the process of activation of the discrete (single, rhythmic) contraction of vertebrate phasic muscles are presented. The revealed differences between the studied muscles reflect adaptive rearrangement levels of ionic mechanisms of the electromechanical coupling system in these muscles, which are achieved in the course of evolution of their contractile function.     

Distinct mechanisms for dysfunctions of mutated ryanodine receptor isoforms

Ryanodine receptor (RyR) is the Ca²⁺-induced Ca²⁺ release channel in cells. RyR1 and RyR2 are its isoforms expressed in the skeletal and cardiac muscles, respectively. Their missense mutations, which are clustered in three regions that correspond to each other, cause hereditary disorders such as malignant hyperthermia and central core disease in skeletal muscle and catecholaminergic polymorphic ventricular tachycardia in cardiac muscle. Their pathogeneses, however, are not well understood. The following hypotheses are favorably discussed in this article: phenotypes with RyR1 and RyR2 mutations are mainly caused by dysregulations of their functions through the interdomain interaction and luminal Ca²⁺, respectively.     

Troponin T isoforms and posttranscriptional modifications: Evolution, regulation and function

Troponin-mediated Ca²⁺-regulation governs the actin-activated myosin motor function which powers striated (skeletal and cardiac) muscle contraction. This review focuses on the structure–function relationship of troponin T, one of the three protein subunits of the troponin complex. Molecular evolution, gene regulation, alternative RNA splicing, and posttranslational modifications of troponin T isoforms in skeletal and cardiac muscles are summarized with emphases on recent research progresses. The physiological and pathophysiological significances of the structural diversity and regulation of troponin T are discussed for impacts on striated muscle function and adaptation in health and diseases.     

Lysophospholipid-mediated alterations in the calcium transport systems of skeletal and cardiac muscle sarcoplasmic reticulum

Summary The effects of various lysophospholipids on the calcium transport activity of sarcoplasmic reticulum (SR) from rabbit skeletal and canine cardiac muscles were examined. The lipids decreased calcium transport activity in both membrane types; the effectiveness being in the order lysoPC > lsyoPS, lysoPG > lysoPE. The maximum inhibition induced by lysoPC, lysoPG and lysoPS was greater than 85% of the normal Ca²⁺-transport rate. In cardiac SR lysoPE had a maximal inhibition of about 50%. Half maximal inhibition of calcium transport by lysoPC was achieved at 110 nmoles lysoPC/mg SR. At this concentration of lysoPC, the (Ca²⁺ + Mg²⁺)-ATPase and Ca²⁺-uptake activities were inhibited to the same extent (about 60%) in skeletal sarcoplasmic reticulum, while in cardiac sarcoplasmic reticulum, there was less than 20% inhibition of the Ca²⁺ + Mg²⁺-ATPase activity. Studies with EGTA-induced passive calcium efflux showed that up to 200 nmoles lysoPC/mg SR did not alter calcium permeability significantly in cardiac sarcoplasmic reticulum. In skeletal muscle membranes the lysophospholipid mediated decrease in calcium uptake correlated well with the increase in passive calcium efflux due to lysophosphatidylcholine. The difference in the lysophospholipid-induced effects on the sarcoplasmic reticulum from the two muscle types probably reflects variations in protein and other membrane components related to the respective calcium transport systems.     

Mitsugumin 53 attenuates the activity of sarcoplasmic reticulum Ca2+-ATPase 1a (SERCA1a) in skeletal muscle

Mitsugumin 53 (MG53) is a member of the membrane repair system in skeletal muscle. However, the roles of MG53 in the unique functions of skeletal muscle have not been addressed, although it is known that MG53 is expressed only in skeletal and cardiac muscle. In the present study, MG53-binding proteins were examined along with proteins that mediate skeletal muscle contraction and relaxation using the binding assays of various MG53 domains and quadrupole time-of-flight mass spectrometry. MG53 binds to sarcoplasmic reticulum Ca²⁺-ATPase 1a (SERCA1a) via its tripartite motif (TRIM) and PRY domains. The binding was confirmed in rabbit skeletal muscle and mouse primary skeletal myotubes by co-immunoprecipitation and immunocytochemistry. MG53 knockdown in mouse primary skeletal myotubes increased Ca²⁺-uptake through SERCA1a (more than 35%) at micromolar Ca²⁺ but not at nanomolar Ca²⁺, suggesting that MG53 attenuates SERCA1a activity possibly during skeletal muscle contraction or relaxation but not during the resting state of skeletal muscle. Therefore MG53 could be a new candidate for the diagnosis and treatment of patients with Brody syndrome, which is not related to the mutations in the gene coding for SERCA1a, but still accompanies exercise-induced muscle stiffness and delayed muscle relaxation due to a reduction in SERCA1a activity.     

The role of STIM1 and SOCE in smooth muscle contractility

Contraction is a central feature for skeletal, cardiac and smooth muscle; this unique feature is largely dependent on calcium (Ca²⁺) signaling and therefore maintenance of internal Ca²⁺ stores. Stromal interaction molecule 1 (STIM1) is a single-pass transmembrane protein that functions as a Ca²⁺ sensor for the activation store-operated calcium channels (SOCCs) on the plasma membrane in response to depleted internal sarco(endo)plasmic (S/ER) reticulum Ca²⁺ stores. STIM1 was initially characterized in non-excitable cells; however, evidence from both animal models and human mutations suggests a role for STIM1 in modulating Ca²⁺ homeostasis in excitable tissues as well. STIM1-dependent SOCE is particularly important in tissues undergoing sustained contraction, leading us to believe STIM1 may play a role in smooth muscle contraction. To date, the role of STIM1 in smooth muscle is unknown. In this review, we provide a brief overview of the role of STIM1-dependent SOCE in striated muscle and build off that knowledge to investigate whether STIM1 contributes to smooth muscle contractility. We conclude by discussing the translational implications of targeting STIM1 in the treatment of smooth muscle disorders.     

Protein kinase A–dependent modulation of Ca2+ sensitivity in cardiac and fast skeletal muscles after reconstitution with cardiac troponin

Protein kinase A (PKA)-dependent phosphorylation of troponin (Tn)I represents a major physiological mechanism during β-adrenergic stimulation in myocardium for the reduction of myofibrillar Ca²⁺ sensitivity via weakening of the interaction with TnC. By taking advantage of thin filament reconstitution, we directly investigated whether or not PKA-dependent phosphorylation of cardiac TnI (cTnI) decreases Ca²⁺ sensitivity in different types of muscle: cardiac (porcine ventricular) and fast skeletal (rabbit psoas) muscles. PKA enhanced phosphorylation of cTnI at Ser23/24 in skinned cardiac muscle and decreased Ca²⁺ sensitivity, of which the effects were confirmed after reconstitution with the cardiac Tn complex (cTn) or the hybrid Tn complex (designated as PCRF; fast skeletal TnT with cTnI and cTnC). Reconstitution of cardiac muscle with the fast skeletal Tn complex (sTn) not only increased Ca²⁺ sensitivity, but also abolished the Ca²⁺-desensitizing effect of PKA, supporting the view that the phosphorylation of cTnI, but not that of other myofibrillar proteins, such as myosin-binding protein C, primarily underlies the PKA-induced Ca²⁺ desensitization in cardiac muscle. Reconstitution of fast skeletal muscle with cTn decreased Ca²⁺ sensitivity, and PKA further decreased Ca²⁺ sensitivity, which was almost completely restored to the original level upon subsequent reconstitution with sTn. The essentially same result was obtained when fast skeletal muscle was reconstituted with PCRF. It is therefore suggested that the PKA-dependent phosphorylation or dephosphorylation of cTnI universally modulates Ca²⁺ sensitivity associated with cTnC in the striated muscle sarcomere, independent of the TnT isoform.     

The couplonopathies: A comparative approach to a class of diseases of skeletal and cardiac muscle

ConclusionsWe define a novel category of diseases of striated muscle, the couplonopathies, as those that have in common a substantial disruption of the functional unit of Ca²⁺ release for EC coupling, the couplon. Consideration of similarities and differences between the couplons of skeletal and cardiac muscle affords insights into the pathogenesis of several couplonopathies, including MH and CPVT. Specifically, we argue that the allosteric connection among couplon proteins Ca_V1.1 and RyR1 is required for the MH phenotype usually linked to mutations in the RyR channel to also associate with mutations in Ca_V1.1. As an extension of this idea, we propose that the same allosteric interaction underpins the beneficial effects of dantrolene. The absence of a corresponding mechanical connection in cardiac muscle explains the absence of CPVT diseases caused by mutations in Ca_V1.2. Based on mechanistic considerations applicable to both couplons, we identify the plasmalemma as a site of alterations in transport properties, typically consisting of an increase in store-operated calcium entry, secondary to couplon mutations that promote Ca²⁺ release. These secondary changes constitute significant factors in the pathogenesis of MH. Mutations in triadin and calsequestrin have tissue-specific consequences: in the heart they cause couplonopathies associated with either loss of the allosteric control putatively exerted by these proteins on the Ca²⁺ release channel or loss of Ca²⁺ buffer capacity in the SR. In skeletal muscle, the phenotypes are milder or nonexistent because of the narrower range of physiological [Ca²⁺]_SR visited during function, as well as the much greater functional reserve of Ca storage that is present in this tissue. Finally, the effects of variants or ablation of JP-45 demonstrate a control of the DHPR that is unique to skeletal muscle and may be prescribed by the separate channel and sensor functions of the skeletal muscle DHPR.     

The potassium channel opener NS1619 modulates calcium homeostasis in muscle cells by inhibiting SERCA

NS1619 (1,3-dihydro-1-[2-hydroxy-5-(trifluoromethyl)phenyl]-5-(trifluoromethyl)-2H-benzimidazole-2-one) is widely used as a large-conductance Ca²⁺-activated K⁺ (BK_Ca) channel opener. It was previously reported that activation of BK_Ca channels by NS1619 could protect the cardiac muscle against ischaemia and reperfusion injury. This study reports the effects of NS1619 on intracellular Ca²⁺ homeostasis in H9C2 and C2C12 cells as well as its molecular mechanism of action. The effects of NS1619 on Ca²⁺ homeostasis in C2C12 and H9C2 cells were assessed using the Fura-2 fluorescence method. Ca²⁺ uptake by sarcoplasmic reticulum (SR) vesicles isolated from rat skeletal muscles and sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA) activity were measured. The effect of NS1619 on the isometric force of papillary muscle contraction in the guinea pig heart was also examined. H9C2 and C2C12 cells treated with NS1619 released Ca²⁺ from internal stores in a concentration-dependent manner. Ca²⁺ accumulation by the SR vesicles was inhibited by NS1619 treatment. NS1619 also decreased the activity of SERCA derived from rat skeletal muscle. The calcium release from cell internal stores and inhibition of SERCA by NS1619 are pH dependent. Finally, NS1619 had a profound effect on the isometric force of papillary muscle contraction in the guinea pig heart. These results indicate that NS1619 is a potent modulator of the intracellular Ca²⁺ concentration in H9C2 and C1C12 cells due to its interaction with SRs. The primary target of NS1619 is SERCA, which is located in SR vesicles. The effect of NS1619-mediated SERCA inhibition on cytoprotective processes should be considered.     

Influence of monovalent cations on the Ca2+-ATPase of sarcoplasmic reticulum isolated from rabbit skeletal and dog cardiac muscles. An interpretation of transient-state kinetic data

Transient-state kinetics of phosphorylation and dephosphorylation of the Ca²⁺-ATPase of sarcoplasmic reticulum vesicles from rabbit skeletal and dog cardiac muscles were studied in the presence of varying concentrations of monovalent and divalent cations. Monovalent cations affect the two types of sarcoplasmic reticulum differently. When the rabbit skeletal sarcoplasmic reticulum was Ca²⁺ deficient, preincubation with K⁺ (as compared with preincubation with choline chloride) did not affect initial phosphorylation at various concentrations of Ca²⁺, added with ATP to phosphorylate the enzyme. This is in contrast to preincubation with K⁺ of the Ca²⁺-deficient dog cardiac sarcoplasmic reticulum, which resulted in an increase in the phosphoenzyme level. When Ca²⁺ was bound to the rabbit skeletal sarcoplasmic reticulum, K⁺ inhibited E ~ P formation; but under the same conditions, E ~ P formation of dog cardiac sarcoplasmic reticulum was activated by K⁺ at 12 μM Ca²⁺ and inhibited at 0.33 and 1.3 μM Ca²⁺. Li⁺, Na⁺ and K⁺ also have different effects on E ~ P decomposition of skeletal and cardiac sarcoplasmic reticulum. The latter responded less to these cations than the former. Studies with ADP revealed differences between the two types of sarcoplasmic reticulum. For rabbit skeletal sarcoplasmic reticulum, 40% of the phosphoenzyme formed was ‘ADP sensitive’, and the decay of the remaining E ~ P was enhanced by K⁺ and ADP. Dog cardiac sarcoplasmic reticulum yielded about 40–48% ADP-sensitive E ~ P, but the decomposition rate of the remaining E ~ P was close to the rate measured in the absence of ADP. Thus, these studies showed certain qualitative differences in the transformation and decomposition of phosphoenzymes between skeletal and cardiac muscle which may have bearing on physiological differences between the two muscle types.     

S100A1 and calmodulin regulation of ryanodine receptor in striated muscle

The release of Ca²⁺ ions from the sarcoplasmic reticulum through ryanodine receptor calcium release channels represents the critical step linking electrical excitation to muscular contraction in the heart and skeletal muscle (excitation–contraction coupling). Two small Ca²⁺ binding proteins, S100A1 and calmodulin, have been demonstrated to bind and regulate ryanodine receptor in vitro. This review focuses on recent work that has revealed new information about the endogenous roles of S100A1 and calmodulin in regulating skeletal muscle excitation–contraction coupling. S100A1 and calmodulin bind to an overlapping domain on the ryanodine receptor type 1 to tune the Ca²⁺ release process, and thereby regulate skeletal muscle function. We also discuss past, current and future work surrounding the regulation of ryanodine receptors by calmodulin and S100A1 in both cardiac and skeletal muscle, and the implications for excitation–contraction coupling.     

Characterization of Functional TRPV1 Channels in the Sarcoplasmic Reticulum of Mouse Skeletal Muscle

TRPV1 represents a non-selective cation channel activated by capsaicin, acidosis and high temperature. In the central nervous system where TRPV1 is highly expressed, its physiological role in nociception is clearly identified. In skeletal muscle, TRPV1 appears implicated in energy metabolism and exercise endurance. However, how as a Ca²⁺ channel, it contributes to intracellular calcium concentration ([Ca²⁺]_i) maintenance and muscle contraction remains unknown. Here, as in rats, we report that TRPV1 is functionally expressed in mouse skeletal muscle. In contrast to earlier reports, our analysis show TRPV1 presence only at the sarcoplasmic reticulum (SR) membrane (preferably at the longitudinal part) in the proximity of SERCA1 pumps. Using intracellular Ca²⁺ imaging, we directly accessed to the channel functionality in intact FDB mouse fibers. Capsaicin and resiniferatoxin, both agonists as well as high temperature (45°C) elicited an increase in [Ca²⁺]_i. TRPV1-inhibition by capsazepine resulted in a strong inhibition of TRPV1-mediated functional responses and abolished channel activation. Blocking the SR release (with ryanodine or dantrolene) led to a reduced capsaicin-induced Ca²⁺ elevation suggesting that TRPV1 may participate to a secondary SR Ca²⁺ liberation of greater amplitude. In conclusion, our experiments point out that TRPV1 is a functional SR Ca²⁺ leak channel and may crosstalk with RyR1 in adult mouse muscle fibers.     

Ca<Superscript>2+</Superscript> signaling in striated muscle: the elusive roles of triadin,junctin, and calsequestrin

This review focuses on molecular interactions between calsequestrin, triadin, junctin and the ryanodine receptor in the lumen of the sarcoplasmic reticulum. These interactions modulate changes in Ca²⁺ release in response to changes in the Ca²⁺ load within the sarcoplasmic reticulum store in striated muscle and are of fundamental importance to Ca²⁺ homeostasis, since massive adaptive changes occur when expression of the proteins is manipulated, while mutations in calsequestrin lead to functional changes which can be fatal. We find that calsequestrin plays a different role in the heart and skeletal muscle, enhancing Ca²⁺ release in the heart, but depressing Ca²⁺ release in skeletal muscle. We also find that triadin and junctin exert independent influences on the ryanodine receptor in skeletal muscle where triadin alone modifies excitation–contraction coupling, while junctin alone supports functional interactions between calsequestrin and the ryanodine receptor.     

The excitation–contraction coupling mechanism in skeletal muscle

First coined by Alexander Sandow in 1952, the term excitation–contraction coupling (ECC) describes the rapid communication between electrical events occurring in the plasma membrane of skeletal muscle fibres and Ca²⁺ release from the SR, which leads to contraction. The sequence of events in twitch skeletal muscle involves: (1) initiation and propagation of an action potential along the plasma membrane, (2) spread of the potential throughout the transverse tubule system (T-tubule system), (3) dihydropyridine receptors (DHPR)-mediated detection of changes in membrane potential, (4) allosteric interaction between DHPR and sarcoplasmic reticulum (SR) ryanodine receptors (RyR), (5) release of Ca²⁺ from the SR and transient increase of Ca²⁺ concentration in the myoplasm, (6) activation of the myoplasmic Ca²⁺ buffering system and the contractile apparatus, followed by (7) Ca²⁺ disappearance from the myoplasm mediated mainly by its reuptake by the SR through the SR Ca²⁺ adenosine triphosphatase (SERCA), and under several conditions movement to the mitochondria and extrusion by the Na⁺/Ca²⁺ exchanger (NCX). In this text, we review the basics of ECC in skeletal muscle and the techniques used to study it. Moreover, we highlight some recent advances and point out gaps in knowledge on particular issues related to ECC such as (1) DHPR-RyR molecular interaction, (2) differences regarding fibre types, (3) its alteration during muscle fatigue, (4) the role of mitochondria and store-operated Ca²⁺ entry in the general ECC sequence, (5) contractile potentiators, and (6) Ca²⁺ sparks.     

Adaptation of striated muscles to Wolframin deficiency in mice: Alterations in cellular bioenergetics

BackgroundWolfram syndrome (WS), caused by mutations in WFS1 gene, is a multi-targeting disease affecting multiple organ systems. Wolframin is localized in the membrane of the endoplasmic reticulum (ER), influencing Ca²⁺ metabolism and ER interaction with mitochondria, but the exact role of the protein remains unclear. In this study we aimed to characterize alterations in energy metabolism in the cardiac and in the oxidative and glycolytic skeletal muscles in Wfs1-deficiency.MethodsAlterations in the bioenergetic profiles in the cardiac and skeletal muscles of Wfs1-knock-out (KO) male mice and their wild type male littermates were determined using high resolution respirometry, quantitative RT-PCR, NMR spectroscopy, and immunofluorescence confocal microscopy.ResultsOxygen consumption without ATP synthase activation (leak) was significantly higher in the glycolytic muscles of Wfs1 KO mice compared to wild types. ADP-stimulated respiration with glutamate and malate was reduced in the Wfs1-deficient cardiac as well as oxidative and glycolytic skeletal muscles.ConclusionsWfs1-deficiency in both cardiac and skeletal muscles results in functional alterations of energy transport from mitochondria to ATP-ases. There was a substrate-dependent decrease in the maximal Complex I –linked respiratory capacity of the electron transport system in muscles of Wfs1 KO mice. Moreover, in cardiac and gastrocnemius white muscles a decrease in the function of one pathway were balanced by the increase in the activity of the parallel pathway.General significanceThis work provides new insights to the muscle involvement at early stages of metabolic syndrome like WS as well as developing glucose intolerance.