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1.
Smooth muscles are important constituents of vertebrate organisms that provide for contractile activity of internal organs and blood vessels. Basic molecular mechanism of both smooth and striated muscle contractility is the force-producing ATP-dependent interaction of the major contractile proteins, actin and myosin II molecular motor, activated upon elevation of the free intracellular Ca2+ concentration ([Ca2+]i). However, whereas striated muscles display a proportionality of generated force to the [Ca2+]i level, smooth muscles feature molecular mechanisms that modulate sensitivity of contractile machinery to [Ca2+]i. Phosphorylation of proteins that regulate functional activity of actomyosin plays an essential role in these modulatory mechanisms. This provides an ability for smooth muscle to contract and maintain tension within a broad range of [Ca2+]i and with a low energy cost, unavailable to a striated muscle. Detailed exploration of these mechanisms is required to understand the molecular organization and functioning of vertebrate contractile systems and for development of novel advances for treating cardiovascular and many other disorders. This review summarizes the currently known and hypothetical mechanisms involved in regulation of smooth muscle Ca2+-sensitivity with a special reference to phosphorylation of regulatory proteins of the contractile machinery as a means to modulate their activity.  相似文献   

2.
Ca2+ release from intracellular stores and influx from extracellular reservoir regulate a wide range of physiological functions including muscle contraction and rhythmic heartbeat. One of the most ubiquitous pathways involved in controlled Ca2+ influx into cells is store-operated Ca2+ entry (SOCE), which is activated by the reduction of Ca2+ concentration in the lumen of endoplasmic or sarcoplasmic reticulum (ER/SR). Although SOCE is pronounced in non-excitable cells, accumulating evidences highlight its presence and important roles in skeletal muscle and heart. Recent discovery of STIM proteins as ER/SR Ca2+ sensors and Orai proteins as Ca2+ channel pore forming unit expedited the mechanistic understanding of this pathway. This review focuses on current advances of SOCE components, regulation and physiologic and pathophysiologic roles in muscles. The specific property and the dysfunction of this pathway in muscle diseases, and new directions for future research in this rapidly growing field are discussed. [BMB Reports 2014; 47(2): 69-79]  相似文献   

3.
Ca2+-regulated motility is essential to numerous cellular functions, including muscle contraction. Systems with troponin C, myosin light chain, or calmodulin as the Ca2+ receptor have evolved in striated muscle and other types of cells to transduce the cytoplasm Ca2+ signals into allosteric conformational changes of contractile proteins. While these Ca2+ receptors are homologous proteins, their coupling to the responding elements is quite different in various cell types. The Ca2+ regulatory system in vertebrate striated muscle represents a highly specialized such signal transduction pathway consisting of the troponin complex and tropomyosin associated with the actin filament. To understand the molecular mechanism in the Ca2+ regulation of muscle contraction and cell motility, we have revealed a preserved ancestral close linkage between the genes encoding two of the troponin subunits, troponin I and troponin T, in the genome of mouse. The data suggest that the troponin I and troponin T genes may have originated from a single locus and evolved in parallel to encode a striated muscle-specific adapter to couple the Ca2+ receptor, troponin C, to the actin–myosin contractile machinery. This hypothesis views the three troponin subunits as two structure–function domains: the Ca2+ receptor and the signal transducing adapter. This model may help to further our understanding of the Ca2+ regulation of muscle contraction and the structure–function relationship of other potential adapter proteins which are converged to constitute the Ca2+ signal transduction pathways governing nonmuscle cell motility. Received: 15 April 1999 / Accepted: 15 July 1999  相似文献   

4.
Myogenic, or pressure-induced, vasoconstriction is critical for local blood flow autoregulation. Underlying this vascular smooth muscle (VSM) response are events including membrane depolarization, Ca2+ entry and mobilization, and activation of contractile proteins. Large conductance, Ca2+-activated K+ channel (BKCa) has been implicated in several of these steps including, (1) channel closure causing membrane depolarization, and (2) channel opening causing hyperpolarization to oppose excessive pressure-induced vasoconstriction. As multiple mechanisms regulate BKCa activity (subunit composition, membrane potential (Em) and Ca2+ levels, post-translational modification) tissue level diversity is predicted. Importantly, heterogeneity in BKCa channel activity may contribute to tissue-specific differences in regulation of myogenic vasoconstriction, allowing local hemodynamics to be matched to metabolic requirements. Knowledge of such variability will be important to exploiting the BKCa channel as a therapeutic target and understanding systemic effects of its pharmacological manipulation.  相似文献   

5.
We investigated the contractile phenotype of skeletal muscle deficient in exons MEx1 and MEx2 (KO) of the titin M-band by using the cre-lox recombination system and a multidisciplinary physiological approach to study skeletal muscle contractile performance. At a maximal tetanic stimulation frequency, intact KO extensor digitorum longus muscle was able to produce wild-type levels of force. However, at submaximal stimulation frequency, force was reduced in KO mice, giving rise to a rightward shift of the force-frequency curve. This rightward shift of the force-frequency curve could not be explained by altered sarcoplasmic reticulum Ca2+ handling, as indicated by analysis of Ca2+ transients in intact myofibers and expression of Ca2+-handling proteins, but can be explained by the reduced myofilament Ca2+ sensitivity of force generation that we found. Western blotting experiments suggested that the excision of titin exons MEx1 and MEx2 did not result in major changes in expression of titin M-band binding proteins or phosphorylation level of the thin-filament regulatory proteins, but rather in a shift toward expression of slow isoforms of the thick-filament-associated protein, myosin binding protein-C. Extraction of myosin binding protein-C from skinned muscle normalized myofilament Ca2+ sensitivity of the KO extensor digitorum longus muscle. Thus, our data suggest that the M-band region of titin affects the expression of genes involved in the regulation of skeletal muscle contraction.  相似文献   

6.
BK_(Ca)通道是细胞膜上受Ca~(2+)和膜电位双重调控的离子通道,其与细胞信号系统偶联并发挥着重要作用,该通道高度表达于高等动物的多种组织.最近的研究证实,在心肌细胞膜上存在力敏感BK通道并参与了心脏收缩与舒张的调控.本文将介绍BK通道与L-型钙通道功能上的耦合,心肌细胞质膜力敏感BK通道门控和功能的研究,以及对基底刚度的响应.这有助于更好地理解力敏感离子通道相关心脏疾病的病理和生理学基础.  相似文献   

7.
Different interacting signaling modules involving Ca2+/calmodulin-dependent myosin light chain kinase, Ca2+-independent regulatory light chain phosphorylation, myosin phosphatase inhibition, and actin filament-based proteins are proposed as specific cellular mechanisms involved in the regulation of smooth muscle contraction. However, the relative importance of specific modules is not well defined. By using tamoxifen-activated and smooth muscle-specific knock-out of myosin light chain kinase in mice, we analyzed its role in tonic airway smooth muscle contraction. Knock-out of the kinase in both tracheal and bronchial smooth muscle significantly reduced contraction and myosin phosphorylation responses to K+-depolarization and acetylcholine. Kinase-deficient mice lacked bronchial constrictions in normal and asthmatic airways, whereas the asthmatic inflammation response was not affected. These results indicate that myosin light chain kinase acts as a central participant in the contractile signaling module of tonic smooth muscle. Importantly, contractile airway smooth muscles are necessary for physiological and asthmatic airway resistance.  相似文献   

8.
When the (pHi) surrounding myofilaments of striated muscle is reduced there is an inhibition of both the actin-myosin reaction as well as the Ca2+-sensitivity of the myofilaments. Although the mechanism for the effect of acidic pH on Ca2+-sensitivity has been controversial, we have evidence for the hypothesis that acidic pH reduces the affinity of troponin C (TNC) for Ca2+. This effect of acidic pH depends not only on a direct effect of protons on Ca2+-binding to TNC, but also upon neighboring thin filament proteins, especially TNI, the inhibitory component of the TN complex. Using flourescent probes that report Ca2+-binding to the regulatory sites of skeletal and cardiac TNC, we have shown, for example, that acidic pH directly decreases the Ca2+-affinity of TNC, but only by a relatively small amount. However, with TNC in whole TN or in the TNI-TNC complex, there is about a 2-fold enhancement of the effects of acidic pH on Ca2+-binding to TNC. Acidic pH decreases the affinity of skeletal TNI for skeletal TNC, and also influences the micro-environment of a probe postioned at Cys-133 of TNI, a region of interaction with TNC. Other evidence that the effects of acidic pH on Ca2+-TNC activation of myofilaments are influenced by TNI comes from studies with developing hearts. In contrast, to the case with the adult preparations, Ca2+-activation of detergent extracted fibers prepared from dog or rat hearts in the peri-natal period are weakly affected by a drop in pH from 7.0 to 6.5. This difference in the effect of acidic (pHi) appears to be due to a difference in the isoform population of TNI, and not to differences in isotype population or amount of TNC.  相似文献   

9.
10.
Guanylate cyclase activating proteins (GCAPs) serve as neuronal Ca2+-sensor proteins in vertebrate rod and cone photoreceptor cells. Zebrafish express in their retina a variety of six different GCAPs, of which four are specific for cone cells. One isoform, zGCAP4, is mainly expressed in double cones and long single cones. We cloned the zGCAP4 gene, purified non-myristoylated and myristoylated forms of the protein after heterologous expression in Escherichia coli and studied its properties: zGCAP4 was a strong activator of membrane-bound guanylate cyclases from bovine and zebrafish retina, showing half-maximal activation at 520–570 nM free Ca2+ concentration. Furthermore, the Ca2+-sensitive activation properties of non-myristoylated and myristoylated zGCAP4 were similar, indicating no influence of the myristoyl moiety on Ca2+-sensor function. Myristoylated zGCAP4 showed low affinity for membranes and did not exhibit a Ca2+–myristoyl switch, a feature typical of some but not all neuronal Ca2+-sensor proteins. However, tryptophan fluorescence studies and Ca2+-dependent differences in protease accessibility revealed Ca2+-induced conformational changes in myristoylated and non-myristoylated zGCAP4, indicating the operation as a Ca2+ sensor. Thus, expression and biochemical properties of zGCAP4 are in agreement with its function as an efficient Ca2+-sensitive regulator of guanylate cyclase activity in cone vision.  相似文献   

11.
Calmodulin (CAM) is a modulatory protein that regulates cellular activity by binding to a large number of proteins. Key elements in the Ca2+-dependent mechanism of interaction between CAM and the proteins it activates are the selectivity for Ca2+ ions and the requirement for Ca2+-dependent conformational changes. We report on results from a series of molecular dynamics simulations that identified discrete steps in the mechanism of structural rearrangement of CAM. The findings implicate the side chains of arginine residues in the bending of the central alpha helix. Structural and energetic considerations point to a dynamic hydrogen bonding pattern around the arginine residues as a ratcheting-type mechanism, causing the kinking of the central helix in consecutive steps stabilized by each new pattern of hydrogen bonds. Initial model building studies to locate potential binding sites of ligands such as trifluoperazine (TFP) indicate that the compaction of CAM results in several structural changes, that explain the selective binding of molecules such as TFP in the N-terminal domain. The present studies identify specific residues involved in the process of compaction and point to specific CAM residues involved in the binding of the ligand. These insights lead directly to propositions for experimental engineering of the molecular structure of CAM in order to probe the hypotheses and their consequences for the function of this important protein.  相似文献   

12.
The regulation of intracellular Ca2+ is essential for cardiomyocyte function, and alterations in proteins that regulate Ca2+ influx have dire consequences in the diseased heart. Low voltage-activated, T-type Ca2+ channels are one pathway of Ca2+ entry that is regulated according to developmental stage and in pathological conditions in the adult heart. Cardiac T-type channels consist of two main types, Cav3.1 (α1G) and Cav3.2 (α1H), and both can be induced in the myocardium in disease and injury but still, relatively little is known about mechanisms for their regulation and their respective functions. This article integrates previous data establishing regulation of T-type Ca2+ channels in animal models of cardiac disease, with recent data that begin to address the functional consequences of cardiac Cav3.1 and Cav3.2 Ca2+ channel expression in the pathological setting. The putative association of T-type Ca2+ channels with Ca2+ dependent signaling pathways in the context of cardiac hypertrophy is also discussed.  相似文献   

13.
Skeletal muscle is a highly organized tissue that has to be optimized for fast signalling events conveying electrical excitation to contractile response. The site of electro-chemico-mechanical coupling is the skeletal muscle triad where two membrane systems, the extracellular t-tubules and the intracellular sarcoplasmic reticulum, come into very close contact. Structure fits function here and the signalling proteins DHPR and RyR1 were the first to be discovered to bridge this gap in a conformational coupling arrangement. Since then, however, new proteins and more signalling cascades have been identified just in the last decade, adding more diversity and fine tuning to the regulation of excitation-contraction coupling (ECC) and control over Ca2+ store content. The concept of Ca2+ entry into working skeletal muscle has become attractive again with the experimental evidence summarized in this review. Store-operated Ca2+ entry (SOCE), excitation-coupled Ca2+ entry (ECCE), action-potential-activated Ca2+ current (APACC), and retrograde EC-coupling (ECC) are new concepts additional to the conventional orthograde ECC; they have provided fascinating new insights into muscle physiology. In this review, we discuss the discovery of these pathways, their potential roles, and the signalling proteins involved that show that the triad may become a crowded place in time.  相似文献   

14.
In the last 15 years, remarkable progress has been realized in identifying the genes that encode the ion-transporting proteins involved in exocrine gland function, including salivary glands. Among these proteins, Ca2+-dependent K+ channels take part in key functions including membrane potential regulation, fluid movement and K+ secretion in exocrine glands. Two K+ channels have been identified in exocrine salivary glands: (1) a Ca2+-activated K+ channel of intermediate single channel conductance encoded by the KCNN4 gene, and (2) a voltage- and Ca2+-dependent K+ channel of large single channel conductance encoded by the KCNMA1 gene. This review focuses on the physiological roles of Ca2+-dependent K+ channels in exocrine salivary glands. We also discuss interesting recent findings on the regulation of Ca2+-dependent K+ channels by protein–protein interactions that may significantly impact exocrine gland physiology.  相似文献   

15.
In vertebrate striated muscle, troponon-tropomyosin is responsible, in part, not only for transducing the effect of calcium on contractile protein activation, but also for inhibiting actin and myosin interaction when calcium is absent. The regulatory troponin (Tn) complex displays several molecular and calcium binding variations in cardiac muscles of different species and undergoes genetic changes with development and in various pathologic states.Extensive reviews on the role of tropomyosin (Tm) and Tn in the regulation of striated muscle contraction have been published describing the molecular mechanisms involved in contractile protein regulation. In our studies, we have found an increase in Mg2+ ATPase activity in cardiac myofibrils from dystrophic hamsters and in rats with chronic coronary artery narrowing. The abnormalities in myofibrillar ATPase activity from cardiomyopathic hamsters were largely corrected by recombining the preparations with a TnTm, complex isolated from normal hamsters indicating that the TnTm, may play a major role in altered myocardial function. We have also observed down regulation of Ca2+ Mg2+ ATPase of myofibrils from hypertrophic guinea pig hearts, myocardial infarcted rats and diabetic-hypertensive rat hearts. In myosin from diabetic rats, this abnormality was substantially corrected by adding troponin-tropomyosin complex from control hearts. All of these disease models are associated with decreased ATPase activities of pure myosin and in the case of rat and hamster models, shifts of myosin, heavy chain from alpha to beta predominate.In summary, there are three main troponin subunit components which might alter myofibrillar function however, very few direct links of molecular alterations in the regulatory proteins to physiologic and pathologic function have been demonstrated so far.  相似文献   

16.
The voltage-dependent slow channels in the myocardial cell membrane are the major pathway by which Ca2+ ions enter the cell during excitation for initiation and regulation of the force of contraction of cardiac muscle. The slow channels have some special properties, including functional dependence on metabolic energy, selective blockade by acidosis, and regulation by the intracellular cyclic nucleotide levels. Because of these special properties of the slow channels, Ca2+ influx into the myocardial cell can be controlled by extrinsic factors (such as autonomic nerve stimulation or circulating hormones) and by intrinsic factors (such as cellular pH or ATP level). The slow Ca2+ channels of the heart are regulated by cAMP in a stimulatory fashion. Elevation of cAMP produces a very rapid increase in number of slow channels available for voltage activation during excitation. The probability of a slow channel opening and the mean open time of the channel are increased. Therefore, any agent that increases the cAMP level of the myocardial cell will tend to potentiate Isi, Ca2+ influx, and contraction. The myocardial slow Ca2+ channels are also regulated by cGMP, in a manner that is opposite to that of CAMP. The effect of cGMP is presumably mediated by means of phosphorylation of a protein, as for example, a regulatory protein (inhibitory-type) associated with the slow channel. Preliminary data suggest that calmodulin also may play a role in regulation of the myocardial slow Ca2+ channels, possibly mediated by the Ca2+-calmodulin-protein kinase and phosphorylation of some regulatory-type of protein. Thus, it appears that the slow Ca2+ channel is a complex structure, including perhaps several associated regulatory proteins, which can be regulated by a number of extrinsic and intrinsic factors.VSM cells contain two types of Ca2+ channels: slow (L-type) Ca2+ channels and fast (T-type) Ca2+ channels. Although regulation of voltage-dependent Ca2+ slow channels of VSM cells have not been fully clarified yet, we have made some progress towards answering this question. Slow (L-type, high-threshold) Ca2+ channels may be modified by phosphorylation of the channel protein or an associated regulatory protein. In contrast to cardiac muscle where cAMP and cGMP have antagonistic effects on Ca2+ slow channel activity, in VSM, cAMP and cGMP have similar effects, namely inhibition of the Ca2+ slow channels. Thus, any agent that elevates cAMP or cGMP will inhibit Ca2+ influx, and thereby act to produce vasodilation. The Ca2+ slow channels require ATP for activity, with a K0.5 of about 0.3 mM. C-kinase may stimulate the Ca2+ slow channels by phosphorylation. G-protein may have a direct action on the Ca2+ channels, and may mediate the effects of activation of some receptors. These mechanisms of Ca2+ channel regulation may be invoked during exposure to agonists or drugs, which change second messenger levels, thereby controlling vascular tone.  相似文献   

17.
Parvalbumins (PVs) are acidic, intracellular Ca2+‐binding proteins of low molecular weight. They are associated with several Ca2+‐mediated cellular activities and physiological processes. It has been suggested that PV might function as a “Ca2+ shuttle” transporting Ca2+ from troponin‐C (TnC) to the sarcoplasmic reticulum (SR) Ca2+ pump during muscle relaxation. Thus, PV may contribute to the performance of rapid, phasic movements by accelerating the contraction–relaxation cycle of fast‐twitch muscle fibers. Interestingly, PVs promote the generation of power stroke in fish by speeding up the rate of relaxation and thus provide impetus to attain maximal sustainable speeds. However, immunological monitoring of diverse tissues demonstrated that PVs are also present in non‐muscle cells. The axoplasmic transport and various intracellular secretory mechanisms including the endocrine secretions seem to be controlled by the Ca2+ regulation machinery. Any defect in the Ca2+ handling apparatus may cause several clinical problems; for instance, PV deficiency alters the neuronal activity, a key mechanism leading to epileptic seizures. Moreover, atypical relaxation of the heart results in diastolic dysfunction, which is a major cause of heart failure predominantly among the aged people. PV may offer a unique potential to correct defective relaxation in energetically compromised failing hearts through PV gene transfer. Consequently, PV gene transfer may present a new therapeutic approach to correct cellular disturbances in Ca2+ signaling pathways of diseased organs. Hence, PVs appear to be amazingly useful candidate proteins regulating a variety of cellular functions through action on Ca2+ flux management.  相似文献   

18.
A rise in cytoplasmic [Ca2+] due to store-operated Ca2+ entry (SOCE) triggers a plethora of responses, both acute and long term. This leads to the important question of how this initial signal is decoded to regulate specific cellular functions. It is now clearly established that local [Ca2+] at the site of SOCE can vary significantly from the global [Ca2+] in the cytosol. Such Ca2+ microdomains are generated by the assembly of key Ca2+ signaling proteins within the domains. For example, GPCR, IP3 receptors, TRPC3 channels, the plasma membrane Ca2+ pump and the endoplasmic reticulum (ER) Ca2+ pump have all been found to be assembled in a complex and all of them contribute to the Ca2+ signal. Recent studies have revealed that two other critical components of SOCE, STIM1 and Orai1, are also recruited to these regions. Thus, the entire machinery for activation and regulation of SOCE is compartmentalized in specific cellular domains which facilitates the specificity and rate of protein-protein interactions that are required for activation of the channels. In the case of TRPC1-SOC channels, it appears that specific lipid domains, lipid raft domains (LRDs), in the plasma membrane, as well as cholesterol-binding scaffolding proteins such as caveolin-1 (Cav-1), are involved in assembly of the TRPC channel complexes. Thus, plasma membrane proteins and lipid domains as well as ER proteins contribute to the SOCE-Ca2+ signaling microdomain and modulation of the Ca2+ signals per se. Of further interest is that modulation of Ca2+ signals, i.e. amplitude and/or frequency, can result in regulation of specific cellular functions. The emerging data reveal a dynamic Ca2+ signaling complex composed of TRPC1/Orai1/STIM1 that is physiologically consistent with the dynamic nature of the Ca2+ signal that is generated. This review will focus on the recent studies which demonstrate critical aspects of the TRPC1 channelosome that are involved in the regulation of TRPC1 function and TRPC1-SOC-generated Ca2+ signals.  相似文献   

19.
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 CaV1.1 and RyR1 is required for the MH phenotype usually linked to mutations in the RyR channel to also associate with mutations in CaV1.1. 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 CaV1.2. 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.  相似文献   

20.
Cellular migration and contractility are fundamental processes that are regulated by a variety of concerted mechanisms such as cytoskeleton rearrangements, focal adhesion turnover, and Ca2+ oscillations. TRPM4 is a Ca2+-activated non-selective cationic channel (Ca2+-NSCC) that conducts monovalent but not divalent cations. Here, we used a mass spectrometry-based proteomics approach to identify putative TRPM4-associated proteins. Interestingly, the largest group of these proteins has actin cytoskeleton-related functions, and among these nine are specifically annotated as focal adhesion-related proteins. Consistent with these results, we found that TRPM4 localizes to focal adhesions in cells from different cellular lineages. We show that suppression of TRPM4 in MEFs impacts turnover of focal adhesions, serum-induced Ca2+ influx, focal adhesion kinase (FAK) and Rac activities, and results in reduced cellular spreading, migration and contractile behavior. Finally, we demonstrate that the inhibition of TRPM4 activity alters cellular contractility in vivo, affecting cutaneous wound healing. Together, these findings provide the first evidence, to our knowledge, for a TRP channel specifically localized to focal adhesions, where it performs a central role in modulating cellular migration and contractility.  相似文献   

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