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PubMed1998

Regulation of Ca2+ signaling in transgenic mouse cardiac myocytes overexpressing calsequestrin.

To probe the physiological role of calsequestrin in excitation-contraction coupling, transgenic mice overexpressing cardiac calsequestrin were developed. Transgenic mice exhibited 10-fold higher levels of calsequestrin in myocardium and survived into adulthood, but had severe cardiac hypertrophy, with a twofold increase in heart mass and cell size. In whole cell-clamped transgenic myocytes, Ca2+ channel- gated Ca2+ release from the sarcoplasmic reticulum was strongly suppressed, the frequency of occurrence of spontaneous or Ca2+ current-triggered "Ca2+ sparks" was reduced, and the spark perimeter was less defined. In sharp contrast, caffeine-induced Ca2+ transients and the resultant Na+-Ca2+ exchanger currents were increased 10-fold in transgenic myocytes, directly implicating calsequestrin as the source of the contractile-dependent pool of Ca2+. Interestingly, the proteins involved in the Ca2+-release cascade (ryanodine receptor, junctin, and triadin) were downregulated, whereas Ca2+-uptake proteins (Ca2+-ATPase and phospholamban) were unchanged or slightly increased. The parallel increase in the pool of releasable Ca2+ with overexpression of calsequestrin and subsequent impairment of physiological Ca2+ release mechanism show for the first time that calsequestrin is both a storage and a regulatory protein in the cardiac muscle Ca2+-signaling cascade. Cardiac hypertrophy in these mice may provide a novel model to investigate the molecular determinants of heart failure.

Animals↗
PubMed1986

Secondary structure of calsequestrin in solutions and in crystals as determined by Raman spectroscopy.

Calsequestrin has been precipitated with calcium into five different crystal forms: cruciform twins, flat rectangles, thin needles, bipyramids, rectangular prisms, and a sixth precrystalline form, spheres. Raman spectra of the spheres and the cruciform twins are the same. The Raman spectrum of a physiological concentration (10%) of calsequestrin in calcium-free solution is the same as the spectrum of calcium precipitated calsequestrin in the amide I region, and in the C-C stretching region, but these spectra are different in the amide III region. The Raman spectrum of unfolded calsequestrin in 5 M guanidine hydrochloride is quite different from the other spectra, but it is not similar to the spectra of other unfolded proteins. Estimates of secondary structure from the amide I region indicate that calsequestrin in calcium-free solution and calcium-precipitated forms has 40 +/- 5% helix, 30 +/- 4% beta-strand, and 18 +/- 2% reverse turn. Secondary structure estimates calculated from the amide III region are not significantly different. They indicate 41 +/- 5% helix and 36 +/- 6% beta-strand for the precipitated forms, and 32 +/- 5% helix and 39 +/- 6% beta-strand for solutions. Calsequestrin unfolded in 5 M guanidine hydrochloride at 100 mg/ml gives 24 +/- 5% helix and 48 +/- 6% beta-strand.

Calsequestrin↗
PubMed1980

Assembly of the sarcoplasmic reticulum. Cell-free synthesis of te Ca2+ + Mg2+-adenosine triphosphatase and calsequestrin.

Polyadenylated RNA prepared from neonatal rat muscle was translated in a rabbit reticulocyte cell-free system. Two sarcoplasmic reticulum proteins, the Ca2+ + Mg2+-dependent adenosine triphosphatase (ATPase) and calsequestrin, were isolated from the translation mixture by immunoprecipitation, followed by electrophoresis in sodium dodecyl sulfate-polyacrylamide gels. The [35S]methionine-labeled translation products were characterized by molecular weight, peptide mapping, and NH2-terminal sequence analysis. The ATPase synthesized in the cell-free system was found to have the same molecular weight (Mr = 100,000) and [35S]-methionine-labeled peptide map as the mature ATPase. The methionine residue present at the NH2 terminus of the mature ATPase was donated by initiator methionyl-tRNArMet and it became acetylated during translation. These results suggest that the ATPase was synthesized without an NH2-terminal signal sequence. Calsequestrin (Mr - 63,000) was synthesized as a higher molecular weight precursor (Mr = 66,000) that contained an additional [35S]methionine-labeled peptide when compared to mature calsequestrin. The NH2-terminal sequence of the precursor was different from the mature protein. The precursor was processed to a polypeptide with a molecular weight identical with mature calsequestrin when microsomal membranes prepared from canine pancreas were included during translation. These results show that calsequestrin is synthesized with an NH2-terminal signal sequence that is removed during translation. These data add to the evidence that the ATPase and calsequestrin follow distinctly different biosynthetic pathways, even though, ultimately, they are both located in the same membrane.

Acetylation↗
PubMed1984

Characterization of skeletal muscle calsequestrin by 1H NMR spectroscopy.

Calsequestrin (Mr = 44,000) is a calcium-binding (KD congruent to 1 mM, congruent to 50 sites/molecule) protein found in the lumen of the sarcoplasmic reticulum of skeletal muscle. The 1H NMR spectrum of calsequestrin in the calcium-free form is presented and is characteristic of a protein largely in the random coil configuration. A number of peaks in the aromatic region have been assigned based on their chemical shifts and sensitivity to pH. The interaction of this protein with Ca2+ and K+ was studied by 1H NMR. Potassium ion binding to calsequestrin caused broadening and concomitant loss of intensity in both the aromatic and aliphatic regions of the spectrum. Calcium ion binding caused similar effects but at much lower metal ion concentrations. It was found that the binding of Ca2+ to calsequestrin was cooperative (Hill coefficient n = 2.9 +/- 0.2) with a dissociation constant of 0.25 +/- 0.06 mM in the absence of K+. In contrast, K+ showed binding to a single class of independent sites (KD = 0.20 +/- 0.04 M). Calcium binding was also studied by circular dichroism at protein concentrations similar to the NMR experiments. The binding profile and cooperativity (n = 2.0 +/- 0.1, KD = 0.19 +/- 0.04 mM) were in agreement with the 1H NMR results. Circular dichroism studies performed at low protein concentrations to reduce the possible effect of calcium binding on the concentration of free calcium gave similar values of n = 2.42 +/- 0.14 and KD = 0.21 +/- 0.005 mM. This cooperativity was also observed in the presence of 100 mM KCl although the affinity for calcium has been significantly reduced (n = 1.65 +/- 0.09, KD = 0.87 +/- 0.036 mM). In view of the large number of calcium binding sites in calsequestrin, these small Hill coefficients show that calcium binding to calsequestrin is only mildly cooperative.

Animals↗
PubMed1984

Size and shape of rabbit skeletal muscle calsequestrin.

Calsequestrin, a calcium-binding protein isolated from rabbit skeletal muscle sarcoplasmic reticulum, was subjected to physiochemical analysis using sodium dodecyl sulfate gel electrophoresis, gel filtration, sedimentation, viscosity, and circular dichroism techniques. The effects of sodium dodecyl sulfate, alkaline pH, guanidine hydrochloride, and calcium ions on the hydrodynamic properties of the protein were studied. Calsequestrin, in the absence of calcium, had a random coil conformation with an alpha-helical content of 11%. Calsequestrin bound 1.7 mg of sodium dodecyl sulfate per mg of protein resulting in an increase in the alpha-helical content to 20%. The protein was completely random coil in guanidine hydrochloride and had a molecular weight of 42,000 as determined by gel filtration in the presence of this denaturant. Sedimentation equilibrium studies showed that calsequestrin was not subjected to aggregation and had a molecular weight of 38,000. Calsequestrin had a low sedimentation coefficient (2.20 S), a high Stokes radius (45 A), and a high intrinsic viscosity (27.1 ml/g) that increased slightly to 32 ml/g in the presence of guanidine hydrochloride, all indicative of a highly extended structure. Similar studies, performed at pH 9.5, revealed that the protein was even more asymmetric at alkaline pH. Calsequestrin bound 50 mol of calcium ions per mol of protein with an affinity of 1 mM as determined by gel filtration. Calcium binding was accompanied by a change of the protein from a highly extended structure (Rs = 45 A) to a much more compact structure (Rs = 35 A).

Animals↗
PubMed1999

Calsequestrin: more than 'only' a luminal Ca2+ buffer inside the sarcoplasmic reticulum.

In striated muscle, the sarcoplasmic reticulum (SR) Ca2+ release/ryanodine receptor (RyR) channel provides the pathway through which stored Ca2+ is released into the myoplasm during excitation-contraction coupling. Various luminal Ca2+-binding proteins are responsible for maintaining the free [Ca2+] at 10(-3)-10(-4) M in the SR lumen; in skeletal-muscle SR, it is mainly calsequestrin. Here we show that, depending on its phosphorylation state, calsequestrin selectively controls the RyR channel activity at 1 mM free luminal [Ca2+]. Calsequestrin exclusively in the dephosphorylated state enhanced the open probability by approx. 5-fold with a Hill coefficient (h) of 3.3, and increased the mean open time by about 2-fold, i.e. solely dephosphorylated calsequestrin regulates Ca2+ release from the SR. Because calsequestrin has been found to occur mainly in the phosphorylated state in the skeletal-muscle SR for the regulation of RyR channel activity, the dephosphorylation of calsequestrin would appear to be a quintessential physiological event.

Animals↗
PubMed1998

Unchanged protein expression of sarcoplasmic reticulum Ca2+-ATPase, phospholamban, and calsequestrin in terminally failing human myocardium.

The enhanced diastolic Ca2+ levels observed in cardiac myocytes from patients with idiopathic dilated cardiomyopathy (DCM) may be either a consequence of functional impairment of sarcoplasmic reticulum calcium-ATPase (SERCA 2) and its regulator protein phospholamban or due to a reduction in the number of SERCA 2 proteins. As different myocardial membrane preparations may lead to different accumulation of proteins, the present study evaluated two different membrane preparations, in human failing and nonfailing myocardium for comparison of SERCA 2 activity and the protein expression of SERCA 2 and phospholamban. Crude membranes and tissue homo-genates without any centrifugation steps were prepared from human nonfailing hearts (donor hearts, NF, n=18) and terminally failing hearts (heart transplant, DCM, n=18). Calsequestrin protein expression was used as an internal control for overall protein expression. In both crude membranes and homogenates maximal SERCA 2 activity (Vmax) was significantly reduced in failing heart preparations (NF crude membranes, 130+/-8; DCM crude membranes, 102+/-5 nmol ATP/mg protein per minute). In contrast, the protein expression of SERCA 2 (NF crude membranes, 488+/-35; DCM crude membranes, 494+/-42; P=0.92), phospholamban (NF crude membranes, 497+/-51; DCM crude membranes, 496+/-45; P=0.98) and calsequestrin (NF crude membranes, 109+/-06; DCM crude membranes, 107+/-08; P=0.84) was unchanged in NF and DCM hearts in both preparation methods. This was also the case when the protein expression was normalized to calsequestrin protein levels. Preparation of sarcoplasmic reticulum in crude membranes led to enhanced purification and consequently higher SERCA 2, phospholamban, and calsequestrin protein levels in crude membranes than in the homogenates, which was paralleled by an increase in SERCA 2 enzyme activity. In conclusion, the altered Ca2+ handling in DCM may be a consequence of reduced SERCA 2 enzyme activity and not the result of differences in protein expression of the Ca2+ regulating proteins SERCA 2, phospholamban, and calsequestrin in human myocardium. The present study emphasizes the importance of different myocardial membrane preparations with respect to quantitative investigations of protein expression and function.

Adult↗
PubMed2002

Calsequestrin expression and calcium binding is increased in streptozotocin-induced diabetic rat skeletal muscle though not in cardiac muscle.

Altered mechanisms of Ca2+ transport may underlie the contractile dysfunctions that have been frequently reported to occur in diabetic cardiac and skeletal muscle tissues. Calsequestrin, a high-capacity Ca2+-binding protein, is involved in the regulation of the excitation-contraction-relaxation cycle of both skeletal and cardiac muscle fibres. We have investigated the expression of calsequestrin and Ca2+ binding in cardiac and skeletal muscle from streptozotocin-induced diabetic rat. Immunoblotting of microsomal membranes from normal and streptozotocin-induced diabetic muscle revealed no significant changes in heart, but an increase in the relative abundance of calsequestrin and calsequestrin-like proteins in skeletal muscle. In analogy, the overall Ca2+-binding capacity of sarcoplasmic reticulum vesicles from diabetic skeletal muscle was drastically increased. The expression of fast muscle marker proteins was not affected, indicating that no relevant fibre transformation occurred in streptozotocin-treated rat muscles. The up-regulation of the high-capacity Ca2+-binding element calsequestrin might represent a compensatory mechanism of diabetic skeletal muscle. An increased Ca2+-buffering capacity of the sarcoplasmic reticulum lumen might counteract elevated cytosolic Ca2+ levels in diabetes thereby preventing Ca2+-dependent myo-necrosis.

Animals↗
PubMed1991

Cloning and characterization of the gene encoding rabbit cardiac calsequestrin.

A cDNA encoding rabbit cardiac calsequestrin was isolated and characterized. The deduced nascent cardiac calsequestrin contains 409 amino acids of which 26% are acidic residues, and had 93% and 67% aa identity with canine cardiac calsequestrin and rabbit fast-twitch skeletal muscle calsequestrin, respectively. RNA blot analyses indicate that this mRNA is expressed in atrium, ventricle and to a lesser amount in slow-twitch skeletal muscle. This mRNA transcript is not expressed in adult fast-twitch skeletal muscle, smooth muscle, or nonmuscle tissues. Analysis of in vitro skeletal muscle myogenesis using a mouse myoblast cell line C2C12, demonstrates that both cardiac and skeletal calsequestrin isoforms are coproduced during muscle differentiation.

Actins↗
PubMed1987

Characterization of cardiac calsequestrin.

Calsequestrin, a calcium-binding protein found in the sarcoplasmic reticulum of muscle cells, was purified from rabbit and canine cardiac and skeletal muscle tissue. The amino acid compositions and amino-terminal sequences of skeletal and cardiac calsequestrin from rabbit and dog were determined. The amino acid composition of the cardiac form was very similar to the skeletal form. The amino-terminal sequence of the cardiac form was homologous to, but not identical with, the amino-terminal sequence of the skeletal form of the protein. Few species differences in the amino-terminal sequences were observed. The calcium-binding capacity of the cardiac form was half the capacity of the skeletal form although the affinities of the two forms of calsequestrin for Ca2+ were similar (Kd = 1 mM). Calcium binding to the cardiac form induced structural changes in the protein as determined by circular dichroism and intrinsic fluorescence spectroscopy. The alpha-helical content of cardiac calsequestrin increased from 3.5% to 10.9% upon binding calcium, while the intrinsic fluorescence of the protein increased 14%. Potassium ions also affected the conformation of cardiac calsequestrin.

Amino Acid Sequence↗
PubMed1995

Association of triadin with the ryanodine receptor and calsequestrin in the lumen of the sarcoplasmic reticulum.

Triadin is a major membrane protein that is specifically localized in the junctional sarcoplasmic reticulum of skeletal muscle and is thought to play an important role in muscle excitation-contraction coupling. In order to identify the proteins in the skeletal muscle that interact with triadin, the cytoplasmic and luminal domains of triadin were expressed as glutathione S-transferase fusion proteins and immobilized to glutathione-Sepharose to form affinity columns. Using these affinity columns, we find that triadin binds specifically to the ryanodine receptor/Ca2+ release channel and the Ca(2+)-binding protein calsequestrin from CHAPS (3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonic acid)-solubilized skeletal muscle homogenates. The luminal but not the cytoplasmic domain of triadin-glutathione S-transferase fusion protein binds [3H]ryanodine receptor, whereas neither the cytoplasmic nor the luminal portion of triadin binds [3H]PN-200-100-labeled dihydropyridine receptor. In addition, the luminal domain of triadin interacts with calsequestrin in a Ca(2+)-dependent manner and is capable of inhibiting the reassociation of calsequestrin to the junctional face membrane. These results suggest that triadin is the previously unidentified transmembrane protein that anchors calsequestrin to the junctional region of the sarcoplasmic reticulum, and is involved in the functional coupling between calsequestrin and the ryanodine receptor/Ca2+ release channel.

Animals↗
PubMed1998

Cardiac-specific overexpression of mouse cardiac calsequestrin is associated with depressed cardiovascular function and hypertrophy in transgenic mice.

Calsequestrin is a high capacity Ca2+-binding protein in the sarcoplasmic reticulum (SR) lumen. To elucidate the functional role of calsequestrin in vivo, transgenic mice were generated that overexpressed mouse cardiac calsequestrin in the heart. Overexpression (20-fold) of calsequestrin was associated with cardiac hypertrophy and induction of a fetal gene expression program. Isolated transgenic cardiomyocytes exhibited diminished shortening fraction (46%), shortening rate (60%), and relengthening rate (60%). The Ca2+ transient amplitude was also depressed (45%), although the SR Ca2+ storage capacity was augmented, as suggested by caffeine application studies. These alterations were associated with a decrease in L-type Ca2+ current density and prolongation of this channel's inactivation kinetics without changes in Na+-Ca2+ exchanger current density. Furthermore, there were increases in protein levels of SR Ca2+-ATPase, phospholamban, and calreticulin and decreases in FKBP12, without alterations in ryanodine receptor, junctin, and triadin levels in transgenic hearts. Left ventricular function analysis in Langendorff perfused hearts and closed-chest anesthetized mice also indicated depressed rates of contraction and relaxation of transgenic hearts. These findings suggest that calsequestrin overexpression is associated with increases in SR Ca2+ capacity, but decreases in Ca2+-induced SR Ca2+ release, leading to depressed contractility in the mammalian heart.

Amino Acid Sequence↗
PubMed1999

Defective beta-adrenergic receptor signaling precedes the development of dilated cardiomyopathy in transgenic mice with calsequestrin overexpression.

Calsequestrin is a high capacity Ca(2+)-binding protein in the junctional sarcoplasmic reticulum that forms a quaternary complex with junctin, triadin, and the ryanodine receptor. Transgenic mice with cardiac-targeted calsequestrin overexpression show marked suppression of Ca(2+)-induced Ca(2+) release, myocyte hypertrophy, and premature death by 16 weeks of age (Jones, L. R., Suzuki, Y. J., Wang, W., Kobayashi, Y. M., Ramesh, V., Franzini-Armstrong, C., Cleemann, L., and Morad, M. (1998) J. Clin. Invest. 101, 1385-1393). To investigate whether alterations in intracellular Ca(2+) trigger changes in the beta-adrenergic receptor pathway, we studied calsequestrin overexpressing transgenic mice at 7 and 14 weeks of age. As assessed by echocardiography, calsequestrin mice at 7 weeks showed mild left ventricular enlargement, mild decreased fractional shortening with increased wall thickness. By 14 weeks, the phenotype progressed to marked left ventricular enlargement and severely depressed systolic function. Cardiac catheterization in calsequestrin mice revealed markedly impaired beta-adrenergic receptor responsiveness in both 7- and 14- week mice. Biochemical analysis in 7- and 14-week mice showed a significant decrease in total beta-adrenergic receptor density, adenylyl cyclase activity, and the percent high affinity agonist binding, which was associated with increased beta-adrenergic receptor kinase 1 levels. Taken together, these data indicate that alterations in beta-adrenergic receptor signaling precede the development of overt heart failure in this mouse model of progressive cardiomyopathy.

Age Factors↗
PubMed1987

The structure of calsequestrin in triads of vertebrate skeletal muscle: a deep-etch study.

We have examined the structure of calsequestrin in three-dimensional images from deep-etched rotary-replicated freeze fractures of skeletal muscle fibers. We selected a fast-acting muscle because the sarcoplasmic reticulum has an orderly disposition and is rich in internal membranes. Calsequestrin forms a network in the center of the terminal cisternae and is anchored to the sarcoplasmic reticulum membrane, with preference for the junctional portion. The anchorage is responsible for maintaining calsequestrin in the region of the sarcoplasmic reticulum close to the calcium-release channels, and it corroborates the finding that calsequestrin and the spanning protein of the junctional feet may interact with each other in the junctional membrane. Anchoring filaments may be composed of a protein other than calsequestrin.

Animals↗
PubMed1984

Evidence for the presence of calsequestrin in both peripheral and interior regions of sheep Purkinje fibers.

Localization of calsequestrin in sheep Purkinje fibers was determined by indirect immunofluorescence labeling of cryostat sections of sheep myocardium from the intraventricular wall. The results presented show that calsequestrin is present in discrete foci at the peripheral, as well as the interior regions of the cytoplasm. Since Purkinje fibers lack transverse tubules, the presence of calsequestrin at specific foci in the interior regions of the cytoplasm in these cells suggests that calsequestrin is localized in the lumen of peripheral junctional sarcoplasmic reticulum, as well as in the lumen of corbular sarcoplasmic reticulum present in the I band region of the myofibrils. Assuming that the function of calsequestrin is to sequester calcium into the lumen of the sarcoplasmic reticulum, these results imply that two structurally different regions of the sarcoplasmic reticulum function as calcium storage sites in mammalian Purkinje fibers and raises the possibility that calcium storage and/or release from these two sites might be regulated differently.

Animals↗
PubMed1999

A 63 kDa skeletal muscle protein associated with eye muscle inflammation in Graves' disease is identified as the calcium binding protein calsequestrin.

It is generally accepted that thyroid-associated ophthalmopathy (TAO) is an autoimmune disease of the eye muscle (EM) and the surrounding orbital connective tissue in which circulating antibodies play an important role. Antibodies against EM membrane proteins of 63-67kDa mol. wt. seem to be the best markers of ophthalmopathy in patients with autoimmune thyroid disease. We purified a 63 kDa EM protein using SDS-polyacrylamide gel electrophoresis technology and TAO patients' sera as probes, digested the protein with cyanogen bromide and sequenced immunoreactive peptides. We also screened a human EM library with a rabbit antiserum against 63-65 kDa proteins and affinity purified antibodies from a TAO patient's serum that reacted with a 55 kDa EM membrane protein. From partial sequence information and from DNA sequencing of positive cDNA clones, the protein was identified as calsequestrin, a 63 kDa calcium binding protein localized in the sarcoplasmic reticulum of the muscle fiber. As determined by Northern blotting, calsequestrin was expressed in EM and other skeletal muscle but not thyroid or fibroblasts. Calsequestrin is different from the "64 kDa protein", which has been identified as succinate dehydrogenase flavoprotein subunit, which has a corrected mol. wt. of 67 kDa. Serum antibodies against calsequestrin were found in 40% of patients with clinically active TAO, but in only 4% of those with stable eye disease, and in 5% of normal subjects, by immunoblotting. Although it is possible that autoimmunity against calsequestrin plays a role in the progressive EM damage that characterizes ophthalmopathy it is more likely that the antibodies are secondary to a reaction against some other cell membrane protein, such as the novel thyroid and eye muscle shared protein G2s or the TSH receptor.

Adult↗
PubMed1994

Regulation of calcium channel in sarcoplasmic reticulum by calsequestrin.

Gating properties of the Ca2+ channel in sarcoplasmic reticulum (SR) were monitored by measuring the choline permeation of the heavy fraction of SR (HSR) vesicles by the light scattering method. Increase of choline permeation by micromolar Ca2+, which refers to Ca2+ response, was lost when HSR vesicles were incubated overnight with EDTA or EGTA. In parallel, calsequestrin was released from the vesicles. This loss of Ca2+ response could not be inhibited by millimolar Mg2+, but was partially inhibited by submolar KCl. Since it took 3-5 hours to lose the Ca2+ response, calsequestrin may be released from the inside of the vesicles. When HSR vesicles were incorporated into lipid bilayer, open probability of the Ca2+ channel increased when calsequestrin was added to the trans side in the presence of millimolar Ca2+. These results suggest that calsequestrin acts as a regulator of Ca2+ channel in SR membrane.

Animals↗
PubMed1994

Immunochemical quantification of sarcoplasmic reticulum Ca(2+)-ATPase and calsequestrin in muscle biopsies from patients with myotonia congenita and paramyotonia congenita Eulenburg.

A sensitive enzyme-linked immunoadsorbant assay was developed to quantify Ca(2+)-ATPase and calsequestrin from sarcoplasmic reticulum in human muscle biopsies. Tissue levels of Ca(2+)-ATPase and calsequestrin averaged 51.5 +/- 28.1 and 6.4 +/- 1.8 mg/g muscle protein, respectively, in control muscles (means +/- SD, n = 12). The high sensitivity and specificity of the antibodies make the assay a useful tool in the diagnosis of human neuromuscular disorders where defects in sarcoplasmic reticulum function may be expected. The assay was applied to muscle biopsies from patients with myotonia congenita and paramyotonia congenita Eulenburg. The calsequestrin concentration was normal in all patient muscles. The Ca(2+)-ATPase content was also within the normal range but varied considerably with the percentage distribution of slow-twitch fibres. This indicates that the prolonged relaxation observed in the muscles of patients with these disorders is not caused by faulty expression of Ca(2+)-ATPase and calsequestrin.

Adolescent↗