Muscle Microsomes Research Articles

Divergent Mechanisms Leading to Signaling Dysfunction in Embryonic Muscle by Bisphenol A and Tetrabromobisphenol A.

Bisphenol A (BPA) and its brominated derivative tetrabromobisphenol A (TBBPA) are high production volume chemicals used in the manufacture of various consumer products. Although regarded as endocrine disruptors, these chemicals are suspected to exert nongenomic actions on muscle function that are not well understood. Using skeletal muscle microsomes, we examined the effects of BPA and TBBPA on ryanodine receptor type 1 (RyR1), dihydropyridine receptor (DHPR), and sarcoplasmic/endoplasmic reticulum Ca2+ ATPase (SERCA). We assessed the impact of these chemicals on Ca2+ dynamics and signaling in embryonic skeletal myotubes through fluorescent Ca2+ imaging and measurement of resting membrane potential (Vm). TBBPA activated RyR1 and inhibited DHPR and SERCA, inducing a net efflux of Ca2+ from loaded microsomes, whereas BPA exhibited little or no activity at these targets. Regardless, both compounds disrupted the function of intact myotubes. TBBPA diminished and eventually abrogated Ca2+ transients, altered intracellular Ca2+ equilibrium, and caused Vm depolarization. For some cells, BPA caused rapid Ca2+ transient loss without marked changes in cytosolic and sarcoplasmic reticulum Ca2+ levels, likely owing to altered cellular excitability as a result of BPA-induced Vm hyperpolarization. BPA and TBBPA both interfere with skeletal muscle function through divergent mechanisms that impair excitation-contraction coupling and may be exemplary of their adverse outcomes in other muscle types.

Abstract 17608: Identification of a Tissue-specific Very Long-chain Acyl-CoA Synthetase Involved in the Inhibition of ATP-Citrate Lyase (ACL) by ETC-1002: A Novel Mechanism for Cholesterol Biosynthesis Inhibition in the Liver

ETC-1002 is a first-in-class oral small molecule that significantly lowers levels of low- density lipoprotein-cholesterol (LDL-C) by 30-40% in hypercholesterolemic patients with reduced potential for muscle-related adverse events. Our previous investigations into the mechanism of action demonstrated a requirement for acyl-CoA synthetase- (ACS) dependent coenzyme A (CoA) activation of ETC-1002 (ETC-1002-CoA) to inhibit its molecular target, ATP-citrate lyase (ACL), an enzyme upstream of HMG-CoA reductase in the cholesterol biosynthesis pathway. In the present study, we have elucidated a mechanistic basis for tissue-specific inhibition of ACL by providing evidence that ACSVL1 is the ACS isoform that catalyzes the CoA activation of ETC-1002. Genetic silencing of ACSVL1 in McArdle cells prevented the CoA activation of ETC-1002 and consequently its inhibition of de novo cholesterol synthesis. We demonstrate that ACSVL1 is highly expressed in primary human hepatocytes and human liver microsomes. Furthermore, we establish a statin-like regulatory link between ACL activity and cholesterol metabolism by showing that ACL siRNA silencing or pharmacological inhibition by ETC-1002-CoA, leads to increased LDLR expression and activity. Using primary human hepatocytes, we demonstrate the concentration-dependent inhibition of cholesterol synthesis by ETC-1002, an associated increase in mRNA expression of the sterol responsive genes srebp2, hmgr, pcsk9, and ldlr mRNA, and increased LDLR activity. In addition, we demonstrate that ACSVL1 is not expressed in L6 myotubes, primary human skeletal muscle cells, or human skeletal muscle microsomes. Unlike statins, ETC-1002 did not inhibit the de novo synthesis of sterols in skeletal muscle cell cultures, nor promote caspase 3/7 activation. Therefore, by establishing a regulatory link between ACL inhibition and LDLR up-regulation, and by identifying ACSVL1 as the ACS isoform that catalyzes the CoA activation of ETC-1002, we provide evidence for the tissue-specific inhibition of ACL by ETC-1002-CoA that results in LDL-C-lowering without activity in skeletal muscle or associated side effects.

Junctophilin 1 and 2 Proteins Interact with the L-type Ca2+ Channel Dihydropyridine Receptors (DHPRs) in Skeletal Muscle

Junctophilins (JPs) anchor the endo/sarcoplasmic reticulum to the plasma membrane, thus contributing to the assembly of junctional membrane complexes in striated muscles and neurons. Recent studies have shown that JPs may be also involved in regulating Ca2+ homeostasis. Here, we report that in skeletal muscle, JP1 and JP2 are part of a complex that, in addition to ryanodine receptor 1 (RyR1), includes caveolin 3 and the dihydropyridine receptor (DHPR). The interaction between JPs and DHPR was mediated by a region encompassing amino acids 230-369 and amino acids 216-399 in JP1 and JP2, respectively. Immunofluorescence studies revealed that the pattern of DHPR and RyR signals in C2C12 cells knocked down for JP1 and JP2 was rather diffused and characterized by smaller puncta in contrast to that observed in control cells. Functional experiments revealed that down-regulation of JPs in differentiated C2C12 cells resulted in a reduction of intramembrane charge movement and the L-type Ca2+ current accompanied by a reduced number of DHPRs at the plasma membrane, whereas there was no substantial alteration in Ca2+ release from the sterol regulatory element-binding protein. Altogether, these results suggest that JP1 and JP2 can facilitate the assembly of DHPR with other proteins of the excitation-contraction coupling machinery.

Type-2 Iodothyronine 5′Deiodinase in Skeletal Muscle of C57Bl/6 Mice. I. Identity, Subcellular Localization, and Characterization

RT-PCR shows that mouse skeletal muscle contains type-2 iodothyronine deiodinase (D2) mRNA. However, the D2 activity has been hard to measure. Except for newborn mice, muscle homogenates have no detectable activity. However, we have reported D2 activity in mouse muscle microsomes. As the mRNA, activity is higher in slow- than in fast-twitch muscle. We addressed here the major problems in measuring D2 activity in muscle by: homogenizing muscle in high salt to improve yield of membranous structures; separating postmitochondrial supernatant between 38 and 50% sucrose, to eliminate lighter membranes lacking D2; washing these with 0.1 M Na(2)CO(3) to eliminate additional contaminating proteins; pretreating all buffers with Chelex, to eliminate catalytic metals; and eliminating the EDTA from the assay, as this can bind iron that enhances dithiothreitol oxidation and promotes peroxidation reactions. Maximum velocity of T(3) generation by postgradient microsomes from red muscles was approximately 1100 fmol/(h · mg) protein with a Michaelis-Menten constant for T(4) of 1.5 nM. D2-specific activity of Na(2)CO(3)-washed microsomes was 6-10 times higher. The enrichment in D2 activity increased in parallel with the capacity of microsomes to load (sarco/endoplasmic reticulum Ca(2+)-ATPase) and bind Ca(2+) (calsequestrin), indicating that D2 resides in the inner sarcoplasmic reticulum, close to the nuclei. The presence of D3 in the sarcolemma suggests that the most of D2-generated T(3) acts locally. Estimates from maximum velocity, Michaelis-Menten constant, and muscle T(4) content suggest that mouse red, type-1, aerobic mouse muscle fibers can generate physiologically relevant amounts of T(3) and, further, that muscle D2 plays an important role in thyroid hormone-dependent muscle thermogenesis.

Properties of the binding sites of [3H]9-methyl-7-bromoeudistomin D in bovine aortic smooth muscle microsomes.

[3H]9-Methyl-7-bromoeudistomin D ([3H]MBED), a powerful caffeine-like Ca2+ releaser, binds to the caffeine binding site of terminal cisternae of skeletal muscle sarcoplasmic reticulum and activates Ca(2+)-induced Ca2+ release. Properties of the binding site of [3H]MBED were investigated in aortic smooth muscle. The specific activity was higher in microsomes than in other fractions. [3H]MBED binding sites in smooth muscle microsomes were of a single class with a high affinity (KD 50nM), comparable with that in skeletal muscle sarcoplasmic reticulum. Caffeine competitively inhibited [3H]MBED binding, indicating MBED shares the same binding site with caffeine. Solubilization and fractionation of the microsomes gave two fractions of [3H]MBED binding activities. These results suggest that, in smooth muscle, there are multiple binding sites of [3H]MBED and caffeine, which might correspond to different pharmacological actions of caffeine on smooth muscle. Therefore, [3H]MBED, which binds to the different binding sites of caffeine, is useful as a probe for investigation of the actions of caffeine at the molecular level.

Increased 45Ca-efflux from smooth muscle microsomes by a rise in an extramicrosomal Ca ion concentration, and the effect of thymol.

Journal Article Increased 45Ca-efflux from smooth muscle microsomes by a rise in an extramicrosomal Ca ion concentration, and the effect of thymol Get access Tetsuhiro Hisayama, Tetsuhiro Hisayama Department of Chemical Pharmacology, Toho University School of Pharmaceutical Sciences, Miyama, Funabashi, Chiba 274, Japan Search for other works by this author on: Oxford Academic Google Scholar Issei Takayanagi Issei Takayanagi Department of Chemical Pharmacology, Toho University School of Pharmaceutical Sciences, Miyama, Funabashi, Chiba 274, Japan Correspondence. Department of Chemical Pharmacology, Toho University School of Pharmaceutical Sciences, Miyama, Funabashi, Chiba 274, Japan Search for other works by this author on: Oxford Academic Google Scholar Journal of Pharmacy and Pharmacology, Volume 35, Issue 8, August 1983, Pages 532–533, https://doi.org/10.1111/j.2042-7158.1983.tb04828.x Published: 12 April 2011 Article history Received: 28 October 1982 Published: 12 April 2011

Allometric scaling of fatty acyl chains in fowl liver, lung and kidney, but not in brain phospholipids

The phospholipid (PL) fatty acyl chain (FA) composition (mol%) was determined in the kidney, liver, lung and brain of 8 avian species ranging in body mass from 150g (Japanese quail, Coturnix coturnix japonica) to 19kg (turkey, Meleagris gallopavo). In all organs except the brain, docosahexaenoic acid (C22:6 n3, DHA) was found to show a negative allometric scaling (allometric exponent: B=-0.18; -0.20 and -0.24, for kidney, liver and lung, respectively). With minor inter-organ differences, smaller birds had more n3 FAs and longer FA chains in the renal, hepatic and pulmonary PLs. Comparing our results with literature data on avian skeletal muscle, liver mitochondria and kidney microsomes and divergent mammalian tissues, the present findings in the kidney, liver and lung PLs seem to be a part of a general relationship termed "membranes as metabolic pacemakers". Marked negative allometric scaling was found furthermore for the tissue malondialdehyde concentrations in all organs except the brain (B=-0.17; -0.13 and -0.05, respectively). In the liver and kidney a strong correlation was found between the tissue MDA and DHA levels, expressing the role of DHA in shaping the allometric properties of membrane lipids.

The NADPH oxidase inhibitor diphenyleneiodonium is also a potent inhibitor of cholinesterases and the internal Ca2+ pump

Diphenyleneiodonium (DPI) is often used as an NADPH oxidase inhibitor, but is increasingly being found to have unrelated side effects. We investigated its effects on smooth muscle contractions and the related mechanisms. We studied isometric contractions in smooth muscle strips from bovine trachea. Cholinesterase activity was measured using a spectrophotometric assay; internal Ca(2+) pump activity was assessed by Ca(2+) uptake into smooth muscle microsomes. Contractions to acetylcholine were markedly enhanced by DPI (10(-4) M), whereas those to carbachol (CCh) were not, suggesting a possible inhibition of cholinesterase. DPI markedly suppressed contractions evoked by CCh, KCl and 5-HT, and also unmasked phasic activity in otherwise sustained responses. Direct biochemical assays confirmed that DPI was a potent inhibitor of acetylcholinesterase and butyrylcholinesterase (IC(50) approximately 8 x 10(-6) M and 6 x 10(-7) M, respectively), following a readily reversible, mixed non-competitive type of inhibition. The inhibitory effects of DPI on CCh contractions were not mimicked by another NADPH oxidase inhibitor (apocynin), nor the Src inhibitors PP1 or PP2, ruling out an action through the NADPH oxidase signalling pathway. Several features of the DPI-mediated suppression of agonist-evoked responses (i.e. suppression of peak magnitudes and unmasking of phasic activity) are similar to those of cyclopiazonic acid, an inhibitor of the internal Ca(2+) pump. Direct measurement of microsomal Ca(2+) uptake revealed that DPI modestly inhibits the internal Ca(2+) pump. DPI inhibits cholinesterase activity and the internal Ca(2+) pump in tracheal smooth muscle.

Effect of Heating Oxymyoglobin and Metmyoglobin on the Oxidation of Muscle Microsomes

Myoglobin (Mb) and its iron have been proposed to be major prooxidants in cooked meats. To understand the mechanisms and differentiate between the prooxidant and antioxidant potential of oxymyoglobin (OxyMb) and metmyoglobin (MetMb), their prooxidant activity, iron content, solubility, free radical scavenging activity, and iron binding capacity were determined as a function of thermal processing. The ability of native and heat denatured OxyMb and MetMb to promote the oxidation of muscle microsomes was different. MetMb promoted lipid oxidation in both its native and denatured states. Conversely, OxyMb became antioxidative when the protein was heated to temperatures >or=75 degrees C. The increased antioxidant activity of heat denatured OxyMb was likely due to a decrease in its prooxidative activity due to its loss of solubility. These data show that the impact on oxidative reactions of Mb is the result of the balance between its antioxidant and prooxidant activities.

Modulation of Sarcoplasmic Reticulum Function by PST2744 [Istaroxime; (E,Z)-3-((2-Aminoethoxy)imino) Androstane-6,17-dione Hydrochloride)] in a Pressure-Overload Heart Failure Model

PST2744 [Istaroxime; (E,Z)-3-((2-aminoethoxy)imino) androstane-6,17-dione hydrochloride)] is a novel inotropic agent that enhances sarco(endo)plasmic reticulum Ca(2+) ATPase (SERCA) 2 activity. We investigated the istaroxime effect on Ca(2+) handling abnormalities in myocardial hypertrophy/failure (HF). Guinea pig myocytes were studied 12 weeks after aortic banding (AoB) and compared with those of sham-operated animals (sham). The gain of calcium-induced Ca(2+) release (CICR), sarcoplasmic reticulum (SR) Ca(2+) content, Na(+)/Ca(2+) exchanger (NCX) function, and the rate of SR reloading after caffeine-induced depletion (SR Ca(2+) uptake, measured during NCX blockade) were evaluated by measurement of cytosolic Ca(2+) and membrane currents. HF characterization: AoB caused hypertrophy and failure in 100 and 25% of animals, respectively. Although CICR gain during constant pacing was preserved, SR Ca(2+) content and SR Ca(2+) uptake were strongly depressed. Resting Ca(2+) and the slope of the Na(+)/Ca(2+) exchanger current (I(NCX))/Ca(2+) relationship were unchanged by AoB. Istaroxime effects: CICR gain, SR Ca(2+) content, and SR Ca(2+) uptake rate were increased by istaroxime in sham myocytes and, to a significantly larger extent, in AoB myocytes; this led to almost complete recovery of SR Ca(2+) uptake in AoB myocytes. Istaroxime increased resting Ca(2+) and the slope of the I(NCX)/Ca(2+) relationship similarly in sham and AoB myocytes. Istaroxime failed to increase SERCA activity in skeletal muscle microsomes devoid of phospholamban. Thus, clear-cut abnormalities in Ca(2+) handling occurred in this model of hypertrophy, with mild decompensation. Istaroxime enhanced SR function more in HF myocytes than in normal ones; almost complete drug-induced recovery suggests a purely functional nature of SR dysfunction in this HF model.

Laminin-Induced Activation of Rac1 and JNKp46 Is Initiated by Src Family Kinases and Mimics the Effects of Skeletal Muscle Contraction

Binding of laminin to dystroglycan in the dystrophin glycoprotein complex causes signaling through dystroglycan-syntrophin-grb2-SOS1-Rac1-PAK1-JNK. Laminin binding also causes syntrophin tyrosine phosphorylation to initiate signaling. The kinase responsible was investigated here. PP2 and SU6656, specific inhibitors of Src family kinases, decreased the amount of phosphotyrosine syntrophin and decreased the level of active Rac1 in laminin-treated myoblasts, myotubes, or skeletal muscle microsomes. c-Src and c-Fyn both phosphorylate syntrophin, and inhibition of either with specific siRNAs diminishes the level of syntrophin phosphorylation. When the rat gastrocnemius was contracted, the level of Rac1 activation increased compared to that of the relaxed control muscle and Rac1 colocalized with beta-dystroglycan. Similar results were obtained when the muscle was stretched. Contracted muscle also contained more activated c-Jun N-terminal kinase, JNKp46. E3, an expressed protein containing only laminin domains LG4 and LG5, increased the rate of proliferation of myoblasts, and PP2 prevented cell proliferation. In addition, Src family kinases colocalized with activated Rac1 and with laminin-Sepharose in solid-phase binding assays. Thus, contraction, stretching, or laminin binding causes recruitment of Src family kinase to the dystrophin glycoprotein complex, activating Rac1 and inducing downstream signaling. The DGC likely represents a mechanoreceptor in skeletal muscle-regulating muscle growth in response to muscle activity. Src family kinases play an initiating and critical role.

Effects of diltiazem or verapamil on calcium uptake and release from chicken skeletal muscle sarcoplasmic reticulum

The purpose of this study was to determine the effects of 2 Ca2+ channel blockers, verapamil and diltiazem, on calcium loading (active Ca2+ uptake) and the following Ca2+ release induced by silver ion (Ag+) and Ca2+ from the membrane of heavy sarcoplasmic reticulum (SR) of chicken skeletal muscle. A fluorescent probe technique was employed to determine the calcium movement through the SR. Pretreatment of the medium with diltiazem and verapamil resulted in a significant decrease in the active Ca2+ uptake, with IC50 of about 290 micromol/L for verapamil and 260 micromol/L for diltiazem. Inhibition of Ca2+ uptake was not due to the development of a substantial drug-dependent leak of Ca2+ from the SR. It might, in part, have been mediated by a direct inhibitory effect of these drugs on the Ca2+ ATPase activity of the SR Ca2+ pump. We confirmed that Ca2+ channel blockers, administered after SR Ca2+ loading and before induction of Ca2+ release, caused a dose-dependent inhibition of both Ca2+- and Ag+-induced Ca2+ release rate. Moreover, if Ca2+ channel blockers were administered prior to SR Ca2+ loading, in spite of Ca2+ uptake inhibition the same reduction in Ca2+- and Ag+-induced Ca2+ release rate was seen. We showed that the inhibition of Ag+-induced Ca2+ release by L-channel blockers is more sensitive than Ca2+-induced Ca2+ release inhibition, so the IC50 for Ag+- and Ca2+-induced Ca2+ release was about 100 and 310 micromol/L for verapamil and 79 and 330 micromol/L for diltiazem, respectively. Our results support the evidence that Ca2+ channel blockers affect muscle microsome of chicken skeletal muscle by 2 independent mechanisms: first, reduction of Ca2+ uptake rate and Ca2+-ATPase activity inhibition, and second, inhibition of both Ag+- and Ca2+-induced Ca2+ release by Ca2+ release channels. These findings confirm the direct effect of Ca2+ channel blockers on calcium release channels. Our results suggest that even if the SR is incompletely preloaded with Ca2+ because of inhibition of Ca2+ uptake by verapamil and diltiazem, no impairment in Ca2+ release occurs.

Solubilization, purification and reconstitution of Ca 2+-ATPase from bovine pulmonary artery smooth muscle microsomes by different detergents: Preservation of native structure and function of the enzyme by DHPC

The properties of Ca 2+-ATPase purified and reconstituted from bovine pulmonary artery smooth muscle microsomes {enriched with endoplasmic reticulum (ER)} were studied using the detergents 1,2-diheptanoyl-sn-phosphatidylcholine (DHPC), poly(oxy-ethylene)8-lauryl ether (C 12E 8) and Triton X-100 as the solubilizing agents. Solubilization with DHPC consistently gave higher yields of purified Ca 2+-ATPase with a greater specific activity than solubilization with C 12E 8 or Triton X-100. DHPC was determined to be superior to C 12E 8; while that the C 12E 8 was determined to be better than Triton X-100 in active enzyme yields and specific activity. DHPC solubilized and purified Ca 2+-ATPase retained the E1Ca−E1*Ca conformational transition as that observed for native microsomes; whereas the C 12E 8 and Triton X-100 solubilized preparations did not fully retain this transition. The coupling of Ca 2+ transported to ATP hydrolyzed in the DHPC purified enzyme reconstituted in liposomes was similar to that of the native micosomes, whereas that the coupling was much lower for the C 12E 8 and Triton X-100 purified enzyme reconstituted in liposomes. The specific activity of Ca 2+-ATPase reconstituted into dioleoyl-phosphatidylcholine (DOPC) vesicles with DHPC was 2.5-fold and 3-fold greater than that achieved with C 12E 8 and Triton X-100, respectively. Addition of the protonophore, FCCP caused a marked increase in Ca 2+ uptake in the reconstituted proteoliposomes compared with the untreated liposomes. Circular dichroism analysis of the three detergents solubilized and purified enzyme preparations showed that the increased negative ellipticity at 223 nm is well correlated with decreased specific activity. It, therefore, appears that the DHPC purified Ca 2+-ATPase retained more organized and native secondary conformation compared to C 12E 8 and Triton X-100 solubilized and purified preparations. The size distribution of the reconstituted liposomes measured by quasi-elastic light scattering indicated that DHPC preparation has nearly similar size to that of the native microsomal vesicles whereas C 12E 8 and Triton X-100 preparations have to some extent smaller size. These studies suggest that the Ca 2+-ATPase solubilized, purified and reconstituted with DHPC is superior to that obtained with C 12E 8 and Triton X-100 in many ways, which is suitable for detailed studies on the mechanism of ion transport and the role of protein–lipid interactions in the function of the membrane-bound enzyme.

Glycogen- and PP1c-targeting Subunit GM Is Phosphorylated at Ser48 by Sarcoplasmic Reticulum-bound Ca2+-Calmodulin Protein Kinase in Rabbit Fast Twitch Skeletal Muscle

Multifunctional Ca(2+)-calmodulin-dependent protein kinase (CaMKII) is a Ser/Thr protein kinase uniformly distributed within the sarcoplasmic reticulum (SR) of skeletal muscle. In fast twitch muscle, no specific substrates of CaMKII have yet been identified in nonjunctional SR. Previous electron microscopy data showed that glycogen particles containing glycogen synthase (GS) associate with SR at the I band level. Furthermore, recent evidence implicates CaMKII in regulation of glucose and glycogen metabolism. Here, we demonstrate that the glycogen- and protein phosphatase 1-targeting subunit, also known as G(M), selectively localizes to the SR membranes of rabbit skeletal muscle and that G(M) and GS co-localize at the level of the I band. We further show that G(M), GS, and PP1c assemble in a structural complex that selectively localizes to nonjunctional SR and that G(M) is phosphorylated by SR-bound CaMKII and dephosphorylated by PP1c. On the other hand, no evidence for a structural interaction between G(M) and CaMKII was obtained. Using His-tagged G(M) recombinant fragments and site-directed mutagenesis, we demonstrate that the target of CaMKII is Ser(48). Taken together, these data suggest that SR-bound CaMKII participates in the regulation of GS activity through changes in the phosphorylation state of G(M). Based on these findings, we propose that SR-bound CaMKII participates in the regulation of glycogen metabolism, under physiological conditions involving repetitive raises elevations of [Ca(2+)](i).

Laminin-alpha1 globular domains 3 and 4 induce heterotrimeric G protein binding to alpha-syntrophin's PDZ domain and alter intracellular Ca2+ in muscle.

Alpha-syntrophin is a component of the dystrophin glycoprotein complex (DGC). It is firmly attached to the dystrophin cytoskeleton via a unique COOH-terminal domain and is associated indirectly with alpha-dystroglycan, which binds to extracellular matrix laminin. Syntrophin contains two pleckstrin homology (PH) domains and one PDZ domain. Because PH domains of other proteins are known to bind the betagamma-subunits of the heterotrimeric G proteins, whether this is also a property of syntrophin was investigated. Isolated syntrophin from rabbit skeletal muscle binds bovine brain Gbetagamma-subunits in gel blot overlay experiments. Laminin-1-Sepharose or specific antibodies against syntrophin, alpha- and beta-dystroglycan, or dystrophin precipitate a complex with Gbetagamma from crude skeletal muscle microsomes. Bacterially expressed syntrophin fusion proteins and truncation mutants allowed mapping of Gbetagamma binding to syntrophin's PDZ domain; this is a novel function for PDZ domains. When laminin-1 is bound, maximal binding of Gsalpha and Gbetagamma occurs and active Gsalpha, measured as GTP-gamma35S bound, decreases. Because intracellular Ca2+ is elevated in Duchenne muscular dystrophy and Gsalpha is known to activate the dihydropyridine receptor Ca2+ channel, whether laminin also altered intracellular Ca2+ was investigated. Laminin-1 decreases active (GTP-gammaS-bound) Gsalpha, and the Ca2+ channel is inhibited by laminin-1. The laminin alpha1-chain globular domains 4 and 5 region, the region bound by DGC alpha-dystroglycan, is sufficient to cause an effect, and an antibody that specifically blocks laminin binding to alpha-dystroglycan inhibits Gbeta binding by syntrophin in C2C12 myotubes. These observations suggest that DGC is a matrix laminin, G protein-coupled receptor.

Matrix metalloproteinase-2-mediated inhibition of Na+-dependent Ca+ uptake by superoxide radicals (O2*-) in microsomes of pulmonary smooth muscle.

Treatment of microsomes (preferably enriched with endoplasmic reticulum) isolated from bovine pulmonary artery smooth muscle tissue with the O2*- -generating system (hypoxanthine (HPX) plus xanthine oxidase (XO)), markedly stimulated matrix metalloproteinase-2 (MMP-2) activity and also enhanced Ca2+ ATPase activity and ATP-dependent Ca2+ uptake. Pretreatment with superoxide dismutase (SOD) and tissue inhibitor of metalloproteinase (TIMP-2) (50 microg ml(-1)), preserved the increase in MMP-2 activity, Ca2+ ATPase activity and also ATP-dependent Ca2+ uptake in the microsomes. In contrast, Na+-dependent Ca2+ uptake in the microsomes was found to be inhibited by the O2*- - generating system. Additionally, O2*- -induced inhibition of Na+-dependent Ca2+ uptake was reversed by SOD and TIMP-2 (50 microg ml(-1)). Electron microscopy revealed that treatment with the O2*- -generating system did not cause any noticeable damage to the microsomes. O2*- -induced changes in MMP-2 activity, ATP-dependent Ca2+ uptake and Na+-dependent Ca2+ uptake, were not reversed upon pretreatment of the microsomes with a low dose (5 microg ml(-1)) of TIMP-2 which, on the contrary, reversed MMP-2 (1 microg ml(-1))-mediated alteration on these parameters. The inhibition of Na+-dependent Ca2+ uptake by O2*- and MMP-2, overpowered the stimulation of ATP-dependent Ca2+ uptake in the microsomes. Treatment of TIMP-2 (5 microg ml(-1)) with the O2*- -generating system abolished the inhibitory effect of TIMP-2 (5 microg ml(-1)) on MMP-2 (1 microg ml(-1)) (measured by (14)C-gelatin degradation). Overall, the present study suggests that O2*- inactivated TIMP-2, the ambient inhibitor of MMP-2, leading to activation of the ambient proteinase, MMP-2, which subsequently stimulated Ca2+ ATPase activity and ATP-dependent Ca2+ uptake, but inhibited Na+-dependent Ca2+ uptake, resulting in a marked decrease in Ca2+ uptake in the smooth muscle microsomes.

Inhibition of Na+/Ca2+ exchanger by peroxynitrite in microsomes of pulmonary smooth muscle: role of matrix metalloproteinase-2.

Treatment of bovine pulmonary artery smooth muscle microsomes with peroxynitrite (ONOO-) (100 microM) markedly stimulated matrix metalloproteinase-2 (MMP-2) activity and also enhanced Ca2+ATPase activity and ATP-dependent Ca2+ uptake. Pretreatment of the microsomes with vitamin E (1 mM) and TIMP-2 (50 microg/ml) preserved the increase in MMP-2 activity, Ca2+ATPase activity and also ATP-dependent Ca2+ uptake in the microsomes. In contrast, Na(+)-dependent Ca2+ uptake in the microsomes was inhibited by ONOO- and this was found to be reversed by vitamin E (1 mM) and TIMP-2 (50 microg/ml). However, changes caused by ONOO- in MMP-2 activity, ATP-dependent Ca2+ uptake and Na(+)-dependent Ca2+ uptake were not reversed upon pretreatment of the microsomes with a low concentration of 5 microg/ml of TIMP-2 which, on the contrary, reversed MMP-2 (1 microg/ml)-mediated alteration on these parameters. The inhibition of Na(+)-dependent Ca2+ uptake by ONOO- and MMP-2 overpowered the stimulation of ATP-dependent Ca2+ uptake in the microsomes. Treatment with ONOO- abolished the inhibitory effect of TIMP-2 (5 microg/ml) on MMP-2 (1 microg/ml) causing 14C-gelatin degradation. Overall, the present study suggests that ONOO- inactivated TIMP-2, the ambient inhibitor of MMP-2, leading to activation of the ambient proteinase, MMP-2, and subsequently stimulated Ca2+ATPase activity and ATP-dependent Ca2+ uptake, but inhibited Na(+)-dependent Ca2+ uptake, resulting in a marked decrease in Ca2+ uptake in microsomes of bovine pulmonary artery smooth muscle.

Modification of lipid composition and oxidation in porcine muscle and muscle microsomes as affected by dietary supplementation of n-3 with either n-9 or n-6 fatty acids and α-tocopheryl acetate

The effect of different oil combinations: olive oil (20 g/kg), sunflower oil (20 g/kg), linseed oil (5 g/kg) and either olive (15 g/kg) or sunflower oil (15 g/kg) and α-tocopheryl acetate supplementation (200 mg/kg feed) on fatty acid composition and lipid oxidation of pig muscle and muscle microsomes was investigated. The proportions of α-linolenic acid ( P<0.001), eicosapentaenoic acid ( P<0.001) and docosahexaenoic acid ( P<0.05) in neutral lipids were significantly greater when linseed oil was added to diets. However, the proportion of docosahexaenoic acid in polar lipids was not significantly affected by the addition of linseed oil to the diets. Adding n-3 fatty acids in the diet produced a higher ( P<0.05) linoleic acid proportion in muscle neutral lipids, particularly in those groups fed n-9 MUFA. Pigs fed n-9 and n-3 enriched diets had the closest n-6:n-3 ratio to human dietary recommendations. The addition of linseed oil produced a significantly ( P<0.05) lower proportion of oleic acid (C18:1n-9) in polar lipids of muscles from pigs fed olive and linseed oils (OL + LIN), but not in those fed sunflower and linseed when compared with groups fed diets not enriched with linseed oil. Supplementation with 200 mg α-tocopheryl acetate/kg feed also led to higher ( P<0.05) oleic acid concentrations in polar lipids. Muscle from the pigs fed sunflower and linseed oils had significantly ( P<0.05) higher Thiobarbituric acid Reactive Substances (TBARS) values throughout the study compared to those fed olive and linseed oils. α-Tocopheryl acetate supplementation consistently improved lipid stability. No interactions between α-tocopherol and oils were observed on lipid oxidation. Iron-induced peroxidation showed a similar trend to that observed for TBARS development. Iron-induced peroxidation of muscle microsomes showed a similar trend to oxidation in muscle. No interactions were detected between different oils in muscle microsomes. The partial replacement of n-9 MUFA (as olive oil) by n-3 PUFA in diet, results in a small increase in muscle and membrane lipid oxidation and could be an interesting alternative in pig diet formulation.

Skeletal Muscle Signaling Pathway through the Dystrophin Glycoprotein Complex and Rac1

The dystrophin glycoprotein complex has been proposed to be involved in signal transduction. Here we have shown that laminin binding causes syntrophin to recruit Rac1 from the rabbit skeletal muscle. Laminin-Sepharose and syntrophin-Sepharose bind a protein complex containing Rac1 from the muscle membranes. The presence of heparin, which inhibits laminin interactions, prevents recruitment of Rac1. The dystrophin glycoprotein complex recruits Rac1 via syntrophin through a Grb2.Sos1 complex. A syntrophin antibody also prevents recruitment of Rac1, suggesting that the signaling complex requires syntrophin. PAK1 is in turn bound by Rac1. c-Jun NH2-terminal kinase-p46 is phosphorylated and activated only when laminin is present, and the p54 isoform is activated when laminin is depleted or binding is inhibited with heparin. In the presence of laminin, c-Jun is activated in both skeletal muscle microsomes and in C2C12 myoblasts, and proliferation increases in C2C12 myoblasts. We postulate that this pathway signals muscle homeostasis and hypertrophy.

Kinetics and Energetics of Mg2+,ATP-Dependent Ca2+Transport in the Plasma Membrane of Smooth Muscle Cells

Calcium ions play a crucial role in the excitation/contraction coupling in smooth muscles. I would like to interpret the biochemical mechanisms underlying Ca2+ exchange and dynamics of such an exchange in the smooth muscles. Particular emphasis is laid on the examination of kinetic, energetic, and catalytic properties of the membrane-linked energy-dependent Ca2+-transporting systems involved in regulation of the intracellular Ca2+ concentration in smooth muscle cells (SMC). It was suggested that the Mg2+,ATP-dependent plasma membrane calcium pump (Ca2+,Mg2+-ATPase) plays a key role in regulation of the Ca2+ concentration in SMC. The purpose of this review is to analyze some of our own results concerning kinetic, energetic, and catalytic properties of the calcium pump of the SMC plasma membrane. In our experiments, we used different biochemical models (namely, fractions of the membrane subcellular structures, highly purified Ca2+,Mg2+-ATPase of the SMC plasma membrane solubilized and reconstituted in the lyposomes, and suspension of digitonin-treated SMC) and a number of methods (including preparative biochemistry, enzymology, membranology, tracer 45Ca2+ flux analysis, and chemical and enzymological kinetics). We have shown that sodium azide-insensitive Mg2+,ATP-dependent Ca2+ accumulation in ureter smooth muscle microsomes is determined by two components. One component represents the Mg2+,ATP-dependent calcium pump of the sarcoplasmic reticulum functionally potentiated by Ca2+-precipitating permeating anions, oxalate or phosphate and inhibited by thapsigargin or cyclopiazonic acid, the highly selective inhibitors of the calcium pump of sarco(endo)plasmic rerticulum. Another component represents the Mg2+,ATP-dependent calcium pump of the plasma membrane functionally potentiated by phosphate. This pump is not inhibited by thapsigargin and cyclopiazonic acid. The effects of temperature, dielectric permeability (D), and ionic strength on the activity of purified Ca2+,Mg2+-ATPase solubilized from the myometrial sarcolemma were studied. The results suggest that changes in the polarity of the incubation medium markedly affect the activity of transport Ca2+,Mg2+-ATPase, and electrostatic interactions between the enzyme activity center and specific ligands (Mg·ADP-, in particular) significantly contribute to the energetics of ATP hydrolysis. Therefore, our data show that changes in the incubation medium polarity significantly affects the ATP-hydrolase activity of Ca2+,Mg2+-ATPase solubilized from the SMC plasma membranes, and electrostatic interactions between the enzyme active sites and reactants (in particular, Mg·ADP-) contribute to a significant extent to the energetics of ATP hydrolysis. We cannot rule out that under physiological conditions the local D values of the myoplasm may differ from that of water, and, moreover, may change (especially near the membrane surface) depending on the metabolic level of SMC. We suppose that local changes in the cytoplasmic D value will affect the plasma membrane calcium pump and, consequently, the efficiency of control of intracellular Ca2+ homeostasis in smooth muscle. So, our biochemical models are suitable experimental objects for studying the kinetic, energetic, and catalytic properties of the Mg2+,ATP-dependent calcium pump of the SMC plasma membrane. In addition, our data might be useful for screening of the mechanisms underlying the action of different physico-chemical factors involved in modulation of the contraction/relaxation cycle.