Chapter Five - Sarcoplasmic reticulum and calcium signaling in muscle cells: Homeostasis and disease

https://doi.org/10.1016/bs.ircmb.2019.12.007Get rights and content

Abstract

The sarco/endoplasmic reticulum is an extensive, dynamic and heterogeneous membranous network that fulfills multiple homeostatic functions. Among them, it compartmentalizes, stores and releases calcium within the intracellular space. In the case of muscle cells, calcium released from the sarco/endoplasmic reticulum in the vicinity of the contractile machinery induces cell contraction. Furthermore, sarco/endoplasmic reticulum-derived calcium also regulates gene transcription in the nucleus, energy metabolism in mitochondria and cytosolic signaling pathways. These diverse and overlapping processes require a highly complex fine-tuning that the sarco/endoplasmic reticulum provides by means of its numerous tubules and cisternae, specialized domains and contacts with other organelles. The sarco/endoplasmic reticulum also possesses a rich calcium-handling machinery, functionally coupled to both contraction-inducing stimuli and the contractile apparatus. Such is the importance of the sarco/endoplasmic reticulum for muscle cell physiology, that alterations in its structure, function or its calcium-handling machinery are intimately associated with the development of cardiometabolic diseases. Cardiac hypertrophy, insulin resistance and arterial hypertension are age-related pathologies with a common mechanism at the muscle cell level: the accumulation of damaged proteins at the sarco/endoplasmic reticulum induces a stress response condition termed endoplasmic reticulum stress, which impairs proper organelle function, ultimately leading to pathogenesis.

Introduction

A general characteristic of eukaryotic cells is the presence of membrane-lined internal structures, termed organelles, which compartmentalize different cellular functions. Among organelles, the endoplasmic reticulum (ER) is the largest one, comprised by a continuous narrow lumen, enclosed by a single membrane. It was identified in the mid-20th century, in the dawn of cell electron microscopy, as a structure that gives cells their “rugged” appearance (Palade, 1955; Porter et al., 1945). Since its discovery, many functions of the ER have been described (Fig. 1A), which are addressed in the following pages, with special emphasis on calcium handling in muscle cells. In the case of cardiac and skeletal muscle cells, termed myocytes, the ER is particularly dense and ordered, giving them their distinctive striated appearance. Because of this unique specialization, the ER in these cells is named sarcoplasmic reticulum (SR), a term that stems from the Greek word sarco, which means “flesh,” which associates with muscle.

In nucleated cells, and not only in myocytes, the sarco/endoplasmic reticulum (SR/ER) is continuous with the nuclear envelope (NE), which encloses the genetic material. In non-muscular cells, the perinuclear ER consists of stacks of cisternae with sheet morphology, known as the lamellar ER, mainly in charge of protein synthesis. Because of that, it exhibits multiple ribosomes attached to its surface, thereby termed “rough” ER. In contrast, peripheral ER mainly consists of a network of tubules, thus known as tubular ER and since this domain is stripped of ribosomes, it is commonly termed “smooth” ER. When muscle cell precursors, termed myoblasts, differentiate into myocytes, their ER also differentiates into SR, acquiring a structure capable of supporting cell contraction. In both skeletal and cardiac myocytes, the SR becomes highly ordered and aligns with the cell's longitudinal axis. In non-striated muscle cells, termed smooth muscle cells (SMC), the SR is not oriented in a single direction, as in other non-myocytes. These different types of SR organization are related to the ability of myocytes to exert mechanical forces, resulting in either axial or concentric contractions.

Muscle contraction has fascinated researchers since the primal physiological studies. Along with ATP, calcium was early identified as one of the key participants at the biochemical level (Szent-Györgyi, 1975). In its soluble form, calcium exists as a cation (Ca2 +), which can form electrostatic interactions with negatively charged moieties of molecules (e.g., carboxyl groups). Thereby, varying Ca2 + levels can induce conformational changes in proteins, thus acting as a regulator of their function. Such is the case of the muscle contraction machinery, which contracts upon Ca2 + binding.

Interestingly, Ca2 + forms insoluble crystals with phosphate, which is a key intermediate in many cellular reactions (e.g., covalent regulation of protein function through phosphorylation and dephosphorylation). In accordance with that, cells maintain low Ca2 + levels in their cytosol (around 100 nM), but high levels in the extracellular milieu (around 10 mM, 10,000 times higher) (Szent-Györgyi, 1975). Because of this compartmentalization, a concentration gradient drives fast Ca2 + entry to the cytosol upon opening of specialized channels in the plasma membrane of myocytes, termed sarcolemma. This allows Ca2 + to act as a rapid second messenger.

Apart from timing, localization is also important for effective signal transduction. In the case of Ca2 + signals, different mechanisms regulate their spatiotemporal patterns: (i) the localization and selective activation of entry channels, (ii) limited Ca2 + diffusion to the cytoplasm (Al-Baldawi and Abercrombie, 1995; Donahue and Abercrombie, 1987), and (iii) pumps extrude Ca2 + and maintain its low resting levels (Szent-Györgyi, 1975). This system allows for spatially confined and temporally limited Ca2 + signals, which can be orchestrated into complex patterns to regulate multiple processes occurring at overlapping times.

Moreover, Ca2 + entry from the extracellular milieu is not the only source of intracellular Ca2 + signals. Certain organelles store Ca2 + at high levels, and thus, can readily release it to the cytosol using the aforementioned concentration gradient. The SR/ER is one of such organelles, with a resting Ca2 + concentration around 1–2 mM (Szent-Györgyi, 1975). Similar to the plasma membrane, it harbors pumps that remove Ca2 + from the cytosol into its lumen. Thus, the SR/ER is the largest intracellular Ca2 + reservoir, and its lumen acts in a similar fashion as the extracellular milieu in terms of Ca2 + compartmentalization.

The SR/ER is not only a key player in Ca2 + homeostasis, but also participates in many cellular processes. Most notably, the SR/ER is the primary site of synthesis of secretion proteins, as well as those targeted to cellular membranes (Caro and Palade, 1964). Ribosomes attached to the cytosolic side of the ER synthesize peptide chains that are co-translationally translocated to the ER lumen, or inserted at its membrane (Bravo et al., 2013). At the ER lumen, nascent peptides fold into their native conformation assisted by chaperones, which are proteins that prevent the formation of stable misfolded intermediates, prone to aggregation. In the ER, folding proteins become glycosylated in order to reach their native conformation. Furthermore, redox modifications of folding proteins also take place at the ER via enzymes termed foldases, which form and breakdown disulfide bonds. Finally, folding proteins interact with lectins that recognize their glycosylated moieties. These lectins serve as the ER quality control machinery, retaining protein folding intermediates, while letting terminally folded proteins advance to the rest of the secretory pathway (i.e., the cargo-managing organelle, the Golgi apparatus). Given its high concentration at the ER lumen, Ca2 + also plays a relevant role in protein folding, serving as a cofactor for chaperones, foldases and lectins.

Because of the redox reactions occurring at the ER lumen, this site is a privileged environment in terms of redox state. On the one hand, disulfide bond formation requires oxygen as an electron acceptor, which leads to the formation of oxygen reactive species (ROS) (Zeeshan et al., 2016). On the other hand, this mechanism converts the ER lumen in an oxidative environment, which differs from the cytosol (Hwang et al., 1992). Thus, the ER is not only a source of ROS, but its function is also highly sensitive to oxidative stress.

Along with from Ca2 + and protein homeostasis, the ER is also a key site for lipid synthesis. Diglycerides and triglycerides, which are the main components of lipid droplets, are synthesized at the ER surface. The route of phospholipid production also initiates at the SR/ER surface, beginning with the synthesis of phosphatidic acid, which then converts to phosphatidylinositol, phosphatidylcholine, phosphatidylethanolamine or phosphatidylserine (Vance and Tasseva, 2013). Furthermore, the SR/ER also participates in the synthesis of sphingolipids, ceramides and cholesterol (Jacquemyn et al., 2017).

The SR/ER is a highly dynamic organelle that undergoes extensive remodeling with each cell division cycle (Fig. 1B). During mitosis, the ER remains as a group of extended sheets with homogeneous architecture, in striking contrast with the interphase ER described above. These sheets then distribute between the daughter cells by migrating to the poles of the dividing cell (Lu et al., 2009). Interestingly, the ER apparently retains its interconnected nature during mitosis, which contrasts with other organelles that disperse into smaller structures. Of note, although the nuclear envelope (NE) is a very distinct compartment of the SR/ER, its proteins disperse throughout the rest of the SR/ER network during mitosis, and must be reassembled at the end of the process (Yang et al., 1997).

During interphase, the ER maintains its structure through processes such as growth, which requires the synthesis of new lipids and proteins, and degradation, which occurs through selective degradation of ER portions by the lysosomal machinery (termed ER-phagy) (Bravo et al., 2013). ER tubules are also remodeled via branching, fusion and fission, resulting in the interconnected network typical of the tubular ER.

Due to decreased efficiency of quality control, degradation and/or renewal mechanisms, damage accumulates as time passes, in an aging path that occurs at the organismal, cellular and organellar level. A general feature of aging is the accumulation of misfolded proteins and/or protein aggregates that interfere with proper cell function (Agbulut et al., 2000). In the case of the SR, aging results in altered Ca2 + handling, which leads to a slower contraction (Narayanan et al., 1996). When damage accumulation becomes a critical burden, it leads to pro-inflammatory signaling, which, being an adaptive response to clear out damaged structures, also jeopardizes tissue homeostasis (Isaac et al., 2016). Finally, when cellular stress becomes unsolvable, it triggers cell demise pathways (Bravo et al., 2013).

Since the SR/ER constitutes the largest intracellular Ca2 + reservoir, extending throughout the whole cell, it provides localized domains of Ca2 + signaling. The basic element of Ca2 + signaling is the opening of a single Ca2 + channel, which creates a small microdomain of high Ca2 + concentration at the SR/ER surface, thus allowing for fine-tuning of the local Ca2 +-responsive machinery. These Ca2 + signals can also induce the opening of neighboring Ca2 + channels, creating a wave of high Ca2 + concentration across the cell that most notably induces myocyte contraction (Mulder and de Tombe, 1989). Furthermore, these two kinds of Ca2 + signals often coexist, as in the case of cardiac myocytes, which experience never-ending cycles of Ca2 + waves and contraction, yet being able to regulate other local Ca2 +-depending events.

Apart from Ca2 + signaling, the ER is also functionally connected with the rest of the secretory pathway through vesicle traffic. It provides proteins and lipid precursors to the Golgi apparatus, endosomal system, lysosomes, peroxisomes and plasma membrane (Bravo-Sagua et al., 2014). This traffic is essential for proper organelle function and structure. For example, inhibition of cargo export from de ER leads to the disappearance of the Golgi apparatus, and also induces ER stress due to protein accumulation in its lumen. Additionally, the SR/ER allegedly also provides nucleation sites and membranes for other structures, such as lipid droplets (otherwise termed adiposomes) (Murphy and Vance, 1999) and autophagosomes, the latter being engulfing membranes that isolate cytoplasmic material for lysosomal degradation (Axe et al., 2008).

Given that the SR/ER also forms the NE, it has nuclear invaginations termed the nucleoplasmic reticulum, which allows local Ca2 + signaling within the nucleus, thus regulating transcription factors and gene expression (Echevarría et al., 2003). Furthermore, the SR/ER also communicates with other structures through close apposition between membranes, without actual membrane fusion. Within the plasma membrane, contact points allow for localized extracellular Ca2 + entry, in order to refill SR/ER stores (Putney, 1986). Such mechanism activates upon SR/ER Ca2 + depletion, and is thus termed, store-operated Ca2 + entry (SOCE, originally termed capacitative Ca2 + entry). The interface between the SR/ER and mitochondria also requires close proximity to allow efficient lipid and Ca2 + transfer from the SR/ER to the mitochondria (Rizzuto et al., 1998; Rusiñol et al., 1994). In the mitochondrial matrix, Ca2 + stimulates oxidative metabolism and ATP production. In muscle cells, this communication is particularly important, as mitochondria must be positioned near the contractile machinery to provide enough ATP. This proximity is highly dynamic and its remodeling is an adaptive mechanism to cope with varying cellular needs (Bravo et al., 2011). When adverse conditions surpass the cellular adaptive capacity (e.g., chronic ER stress), it leads to sustained SR/ER-to-mitochondria Ca2 + transfer, which in turn, triggers mitochondrial dysfunction and cell death (Bravo-Sagua et al., 2013). Therefore, SR/ER-mitochondria communication serves as a double-edged sword that regulates both cell survival and death.

In sum, Ca2 + handling is spatially and temporally complex, requiring the communication of various organelles. Among them, the SR/ER plays a central role, being highly heterogeneous and dynamic. Through Ca2 + signals, the SR/ER controls a diverse array of functions, such as protein homeostasis, energy metabolism, gene expression and cell fate. Moreover, in muscle cells, all these regulatory networks coexist with whole-cell Ca2 + waves, which allow for cell contraction. In the following pages, we will describe Ca2 + handling in the SR/ER of the three muscle cell types (skeletal fibers, cardiac myocyte and SMC), explore their differences and analyze how their particularities associate with their function and pathological processes.

Section snippets

ER-shaping proteins and dynamics

The SR/ER requires a plethora of specialized proteins to acquire and maintain its shape. In terms of ER laminar structures, the protein Climp63 has been identified as a molecular spacer that maintains the width of the ER sheets. Moreover, Climp63 knock-down in the monkey kidney cell line COS-7 leads to decreased luminal width, without fully eliminating the sheet-shaped ER. Conversely, its overexpression leads to a marked increase in the number of ER sheets (Shibata et al., 2010). Of note,

Differential spatiotemporal Ca2 + handling

Ca2 + exerts its functions through the regulation of several Ca2 +-sensitive proteins with specific domains, such as EF-hand, C2 and annexin Ca2 +-binding domains. Each domain exhibits distinct Ca2 + binding dynamics, which allows for the fine regulation of intra- and/or inter-molecular interactions (Carafoli and Krebs, 2016). Therefore, these domains are probably susceptible to oscillatory Ca2 + changes consisting in series of Ca+ 2 spikes (Ca2 + transient elevations of certain amplitude and

Smooth muscle cell classification

Unlike striated muscle, SMC are very heterogeneous in relation to their location and function (in terms of contraction-relaxation times and mechanisms involved). These types of muscle cells do not have sarcomeres as contraction units; instead they present a network of actin-myosin that drives the contraction in a very particular way (Sweeney and Hammers, 2018). SMC can be classified in different groups; however, since the scope of this work is not the diversity of SMC, we will classify them

SR/ER dysfunction and diseases

The SR/ER is a pivotal organelle in the regulation of intracellular Ca2 +, which is a key second messenger in several pathological pathways. Alterations in Ca2 + uptake or release lead to Ca2 + imbalance, thereby triggering dysfunctional responses in cells. Additionally, the SR is the organelle responsible for protein synthesis, which is a very delicate process. Correct protein folding is carried out by luminal chaperones such as Grp78, Grp94 and Calreticulin, whose activity is Ca2 +-dependent (Xu

Concluding remarks

The SR/ER is a ubiquitous organelle composed of several domains, all of which are distinct in both composition and function. Moreover, the SR/ER undergoes profound specialization depending on the cell type, as well as extensive remodeling, according to both internal and external cues. Muscle cells take the versatility of SR/ER architecture to the extreme, ranging from an apparently disordered network to a densely packed array of parallel cisternae. In either case, the SR/ER participates in cell

Acknowledgments

This work was funded by Comisión Nacional de Ciencia y Tecnología (CONICYT) grants FONDAP 15130011 (R.B.-S., V.G., M.C., V.P., S.L.), FONDECYT 1190743 (V.P.), 1161156 (S.L.), and 1200490 (S.L.). Programa de Investigación Asociativa (PIA)-CONICYT 172066 (V.P.), Installation Program 77170004 2017 (R.B.-S.), and doctoral scholarships to P.S.-A. and F.M.-C. University of Chile grants FIDA/ABCvital 02-2018 (R.B.-S.), U-Inicia UI-006-19 (R.B.-S.) and U-Redes Generación VID G_2018-35 (V.P.) and the

References (308)

  • S. Boateng et al.

    Inhibition of endogenous cardiac phosphatase activity and measurement of sarcoplasmic reticulum calcium uptake: a possible role of phospholamban phosphorylation in the hypertrophied myocardium

    Biochem. Biophys. Res. Commun.

    (1997)
  • R. Bravo et al.

    Endoplasmic reticulum and the unfolded protein response: dynamics and metabolic integration

    Int. Rev. Cell Mol. Biol.

    (2013)
  • R. Bravo-Sagua et al.

    Organelle communication: signaling crossroads between homeostasis and disease

    Int. J. Biochem. Cell Biol.

    (2014)
  • S.E. Burk et al.

    cDNA cloning, functional expression, and mRNA tissue distribution of a third organellar Ca2 + pump

    J. Biol. Chem.

    (1989)
  • E. Carafoli et al.

    Why calcium? How calcium became the best communicator

    J. Biol. Chem.

    (2016)
  • M.A. Carrasco et al.

    Calcium microdomains and gene expression in neurons and skeletal muscle cells

    Cell Calcium

    (2006)
  • E. Chacon et al.

    Mitochondrial free calcium transients during excitation-contraction coupling in rabbit cardiac myocytes

    FEBS Lett.

    (1996)
  • W. Chen et al.

    Phosphorylation of phospholamban in aortic smooth muscle cells and heart by calcium/calmodulin-dependent protein kinase II

    Cell. Signal.

    (1994)
  • S. Currie et al.

    Calcium/calmodulin-dependent protein kinase II activity is increased in sarcoplasmic reticulum from coronary artery ligated rabbit hearts

    FEBS Lett.

    (1999)
  • O.M. de Brito et al.

    Mitofusin-2 regulates mitochondrial and endoplasmic reticulum morphology and tethering: the role of Ras

    Mitochondrion

    (2009)
  • A. Díaz-Vegas et al.

    Skeletal muscle excitation-metabolism coupling

    Arch. Biochem. Biophys.

    (2019)
  • B.S. Donahue et al.

    Free diffusion coefficient of ionic calcium in cytoplasm

    Cell Calcium

    (1987)
  • W. Du et al.

    Ryanodine receptors in muscarinic receptor-mediated bronchoconstriction

    J. Biol. Chem.

    (2005)
  • S.E. Dunn et al.

    Nerve activity-dependent modulation of calcineurin signaling in adult fast and slow skeletal muscle fibers

    J. Biol. Chem.

    (2001)
  • A.C. Elliott

    Recent developments in non-excitable cell calcium entry

    Cell Calcium

    (2001)
  • P.A. Ellison et al.

    Kinetics of smooth muscle heavy meromyosin with one thiophosphorylated head

    J. Biol. Chem.

    (2000)
  • J.M. Eltit et al.

    Membrane electrical activity elicits inositol 1,4,5-trisphosphate-dependent slow Ca2 + signals through a Gbeta-gamma/phosphatidylinositol 3-kinase gamma pathway in skeletal myotubes

    J. Biol. Chem.

    (2006)
  • A.M. Evans

    Nanojunctions of the sarcoplasmic reticulum deliver site- and function-specific calcium signaling in vascular smooth muscles

    Adv. Pharmacol.

    (2017)
  • C.H. Feldman et al.

    The role of STIM1 and SOCE in smooth muscle contractility

    Cell Calcium

    (2017)
  • B.E. Flucher et al.

    Development of the excitation-contraction coupling apparatus in skeletal muscle: association of sarcoplasmic reticulum and transverse tubules with myofibrils

    Dev. Biol.

    (1993)
  • R.C. Foehring et al.

    Relation of whole muscle contractile properties to source of innervation

    Exp. Neurol.

    (1988)
  • V. Garrido-Moreno et al.

    GDF-11 prevents cardiomyocyte hypertrophy by maintaining the sarcoplasmic reticulum-mitochondria communication

    Pharmacol. Res.

    (2019)
  • D. Ghosh et al.

    Calcium channels in vascular smooth muscle

    Adv. Pharmacol.

    (2017)
  • L. Golini et al.

    Junctophilin 1 and 2 proteins interact with the L-type Ca2 + channel dihydropyridine receptors (DHPRs) in skeletal muscle

    J. Biol. Chem.

    (2011)
  • M.F. Gomez et al.

    Opposing actions of inositol 1,4,5-trisphosphate and ryanodine receptors on nuclear factor of activated T-cells regulation in smooth muscle

    J. Biol. Chem.

    (2002)
  • B. Abrenica et al.

    Nucleoplasmic calcium regulation in rabbit aortic vascular smooth muscle cells

    Can. J. Physiol. Pharmacol.

    (2003)
  • O. Agbulut et al.

    Age-related appearance of tubular aggregates in the skeletal muscle of almost all male inbred mice

    Histochem. Cell Biol.

    (2000)
  • M. Aoyama et al.

    Requirement of ryanodine receptors for pacemaker Ca2 + activity in ICC and HEK293 cells

    J. Cell Sci.

    (2004)
  • R. Araya et al.

    Dihydropyridine receptors as voltage sensors for a depolarization-evoked, IP3R-mediated, slow calcium signal in skeletal muscle cells

    J. Gen. Physiol.

    (2003)
  • J. Avila-Medina et al.

    The complex role of store operated calcium entry pathways and related proteins in the function of cardiac, skeletal and vascular smooth muscle cells

    Front. Physiol.

    (2018)
  • E.L. Axe et al.

    Autophagosome formation from membrane compartments enriched in phosphatidylinositol 3-phosphate and dynamically connected to the endoplasmic reticulum

    J. Cell Biol.

    (2008)
  • F. Bacou et al.

    Expression of myosin isoforms in denervated, cross-reinnervated, and electrically stimulated rabbit muscles

    Eur. J. Biochem.

    (1996)
  • Y. Bai et al.

    The contribution of inositol 1,4,5-trisphosphate and ryanodine receptors to agonist-induced Ca(2 +) signaling of airway smooth muscle cells

    Am. J. Physiol. Lung Cell. Mol. Physiol.

    (2009)
  • R.A. Bannister

    Bridging the myoplasmic gap II: more recent advances in skeletal muscle excitation-contraction coupling

    J. Exp. Biol.

    (2016)
  • R. Bassel-Duby et al.

    Signaling pathways in skeletal muscle remodeling

    Annu. Rev. Biochem.

    (2006)
  • A. Bergner et al.

    Acetylcholine-induced calcium signaling and contraction of airway smooth muscle cells in lung slices

    J. Gen. Physiol.

    (2002)
  • M.J. Berridge

    Smooth muscle cell calcium activation mechanisms

    J. Physiol.

    (2008)
  • M.J. Berridge et al.

    The versatility and universality of calcium signalling

    Nat. Rev. Mol. Cell Biol.

    (2000)
  • B. Blaauw et al.

    No evidence for inositol 1,4,5-trisphosphate-dependent Ca2 + release in isolated fibers of adult mouse skeletal muscle

    J. Gen. Physiol.

    (2012)
  • M.P. Blaustein et al.

    Sodium/calcium exchange: its physiological implications

    Physiol. Rev.

    (1999)
  • Cited by (29)

    • Strategy for sodium-salt substitution: On the relationship between hypertension and dietary intake of cations

      2022, Food Research International
      Citation Excerpt :

      By promoting Ca2+ chelation and efflux as well as inhibiting absorption, Mg2+ can effectively reduce the intracellular Ca2+ concentration. Besides, Mg2+ can compete with Ca2+ to bind to the site of troponin (Belin & He, 2007), inhibit the contraction produced by the relative slide between myosin thick filaments and actin filaments, regulating the activity and dynamics of contractile proteins (Bravo-Sagua et al., 2020). Intracellular Mg2+ can also serve as a second messenger to regulate Ca2+-related signal transduction (Touyz, Laurant, & Schiffrin, 1998).

    • Lockdown of mitochondrial Ca<sup>2+</sup> extrusion and subsequent resveratrol treatment kill HeLa cells by Ca<sup>2+</sup> overload

      2021, International Journal of Biochemistry and Cell Biology
      Citation Excerpt :

      Calcium ion [Ca2+], the most highlighted, prominent, versatile second messenger is crucially involved in regulating many physiological cellular functions (Bravo-Sagua et al., 2020; Delierneux et al., 2020; Giorgi et al., 2018) which constantly influx and efflux out of mitochondria (Vultur et al., 2018).

    • CRISPR/Cas9-mediated tryptophan hydroxylase 1 knockout decreases calcium transportation in goat mammary epithelial cells

      2021, Biochemical Engineering Journal
      Citation Excerpt :

      In addition to meeting the needs of lactation and maintaining ion homeostasis, calcium itself is also an important regulator of multiple biological processes in cells. Calcium has the functions of forming bones, maintaining muscle and nerve excitability, participating in blood coagulation, and maintaining normal life activities of cells [66,67]. Calmodulin(CaM), the major calcium sensor in most cells, can bind up to four calcium ions, extending the protein to bind cellular targets [68].

    • Ca<sup>2 +</sup> in health and disease

      2021, International Review of Cell and Molecular Biology
    View all citing articles on Scopus

    These authors contributed equally to this work.

    View full text