Reciprocal amplification of ROS and Ca2+ signals in stressed mdx dystrophic skeletal muscle fibers

Muscular dystrophies are among the most severe inherited muscle diseases. The genetic defect is a mutation in the gene for dystrophin, a cytoskeletal protein which protects muscle cells from mechanical damage. Mechanical stress, applied as osmotic shock, elicits an abnormal surge of Ca²⁺ spark-like events in skeletal muscle fibers from dystrophin deficient (mdx) mice. Previous studies suggested a link between changes in the intracellular redox environment and appearance of Ca²⁺ sparks in normal mammalian skeletal muscle. Here, we tested whether the exaggerated Ca²⁺ responses in mdx fibers are related to oxidative stress. Localized intracellular and mitochondrial Ca²⁺ transients, as well as ROS production, were assessed with confocal microscopy. The rate of basal cellular but not mitochondrial ROS generation was significantly higher in mdx cells. This difference was abolished by pre-incubation of mdx fibers with an inhibitor of NAD(P)H oxidase. In addition, immunoblotting showed a significantly stronger expression of NAD(P)H oxidase in mdx muscle, suggesting a major contribution of this enzyme to oxidative stress in mdx fibers. Osmotic shock produced an abnormal and persistent Ca²⁺ spark activity, which was suppressed by ROS-reducing agents and by inhibitors of NAD(P)H oxidase. These Ca²⁺ signals resulted in mitochondrial Ca²⁺ accumulation in mdx fibers and an additional boost in cellular and mitochondrial ROS production. Taken together, our results indicate that the excessive ROS production and the simultaneous activation of abnormal Ca²⁺ signals amplify each other, finally culminating in a vicious cycle of damaging events, which may contribute to the abnormal stress sensitivity in dystrophic skeletal muscle. Drs. V.M. Shkryl and A.S. Martins contributed equally to this work.     

Effects of 2,3-butanedione monoxime on activation of contraction and crossbridge kinetics in intact and chemically skinned smooth muscle fibres from guinea pig taenia coli

Summary The effects of 2,3-butanedione monoxime (BDM) were studied in smooth muscle fibres from guinea pig taenia coli. In intact muscle, active force during contractions induced by high-K⁺ was inhibited by about 10% in 1 mM BDM and by approximately 70% in 10 mM BDM. Intracellular [Ca²⁺] during contraction, measured with the fura-2 technique, was reduced in the presence of BDM. The reduction in force and [Ca²⁺] in the presence of 1 and 10 mM BDM could be reproduced by reduction in extracellular Ca²⁺, suggesting that BDM influences the Ca²⁺ entry or release. In skinned muscle preparations, BDM decreased the Ca²⁺ sensitivity of active force. This change could be explained by a decreased level of myosin light chain phosphorylation. In fibres maximally activated by thiophosphorylation, the effect of BDM on force occurred at higher concentrations; 10 mM gave no reduction of force and 60 mM 15% reduction. The maximal shortening velocity (V _max) and force were unaffected by 30 mM BDM in thiophosphorylated muscle and decreased almost in parallel in Ca²⁺-activated contractions. The present results suggest that BDM inhibits myosin light chain phosphorylation, directly decreases force generation at the crossbridge level and inhibits the Ca²⁺ translocation in smooth muscle. The effect on force in skinned fibres is observed at higher BDM concentrations than those reported to be required for inhibition of force in striated muscle. The inhibition of force in intact smooth muscle could be explained by an influence on Ca²⁺ translocation.     

The effects of metabolic inhibition on force, Ca2+ and pHi in guinea-pig ureteric smooth muscle

 The effect of metabolic inhibition on the contractile function of adult guinea-pig ureter has been investigated. Strips of ureteric smooth muscle were loaded with Indo-1 or SNARF to measure intracellular [Ca²⁺] ([Ca²⁺]_i) or pH (pH_i) simultaneously with force. Inhibiting oxidative phosphorylation with cyanide rapidly reduced phasic contractions and the associated Ca²⁺ transients, after initial transient increases. The effects of cyanide were reversible and related to the amount of contractile activity undertaken. Inhibition of glycolysis with iodoacetate abolished all force. In high-K⁺-depolarised preparations, cyanide reduced the tonic contraction, but this was not accompanied by a reduction in [Ca²⁺]_i, suggesting a desensitisation of the myofilaments. Cyanide produced a fall in pH_i, which may underlie the initial transient increase in force. These data suggest that metabolic inhibition reduces force in the ureter by affecting both excitation and hence the Ca²⁺ transient, and at the myofilaments to reduce their sensitivity to Ca²⁺. Thus when oxidative metabolism is impaired contractile dysfunction may arise in the ureter. Received: 22 July 1997 / Received after revision and accepted: 12 September 1997     

Calcium regulation and muscle disease

Changes in intracellular Ca²⁺-concentration play an important role in the excitation–contraction–relaxation cycle of skeletal muscle. In this review we describe various inheritable muscle diseases to highlight the role of Ca²⁺ -regulatory mechanisms. Upon excitation the ryanodine receptor releases Ca²⁺ in the cytosol. During and after contraction the sarcoplasmic reticulum (SR) Ca²⁺ ATPase (SERCA) pumps Ca²⁺ back in the SR resulting in relaxation. An abnormal change in the intracellular Ca²⁺ -concentration results in defective muscle contraction and/or relaxation, which is the cause of various muscle diseases. Malignant hyperthermia (MH) and central core disease (CCD) are both caused by mutations in the ryanodine receptor but show different clinical phenotypes. In MH an acute increase of Ca²⁺ results in excessive muscle contraction causing rigidity, while in CCD a chronic rise of cytosolic Ca²⁺ is seen, leading to mitochondrial damage, disorganization of myofibrils and muscle weakness. In Brody disease and also in mitochondrial myopathies, SERCA functions sub optimal causing a prolonged physiological Ca²⁺ -elevation leading to slowing of relaxation. Defective actin–myosin interactions, as in nemaline myopathy and also in mitochondrial myopathies due to ATP-shortage, cause Ca²⁺-hyposensitivity and slowness of contraction. Information of Ca²⁺ -kinetics in these inherited muscular diseases improves our understanding of the role of calcium in the physiology and pathophysiology of the skeletal muscle cell.     

Protective effects of Chlorpromazine and Verapamil against cadmium-induced kidney damage in vivo

Overexposure to cadmium (Cd) can induce kidney damage, which was related to the oxidative damage and disturb intracellular Ca²⁺ homeostasis. Chlorpromazine (CPZ), targeting calmodulin (CaM), and the Ca²⁺ channel blocker Verapamil (Ver) are involved in intracellular Ca²⁺ homeostasis processes. The aim of the study was to investigate the kidney damage caused by Cd administrated for 6 weeks and to evaluate the effects of pre-treatment with either chlorpromazine or verapamil on Cd-induced kidney damage. Thirty-two Wistar rats were divided randomly into 4 groups by weight, i.e., control group, Cd-treated group, and CPZ or Ver pre-treated group. The Cd-treated group rats were subcutaneously (s.c.) injected with 7 μmol CdCl₂/kg body weight/day. The CPZ and Ver pre-treated group rats were intraperitoneally (i.p.) injected with 5 mg CPZ/kg body weight/day, 4 mg Ver/kg body weight/day, respectively, 1 h before the s.c. administration of 7 μmol CdCl₂/kg body weight/day. The control group rats were injected s.c. with saline at the same time. The volume of injection was 2 ml/kg body weight, 5 times per week, for up to 6 weeks. After 6 weeks, Cd concentrations in the renal cortex and urine were significantly higher in Cd-treated group than that in controls. Cd concentrations of the urine in CPZ and Ver pre-treated groups were significantly lower than that in Cd-treated group, but there were no significant changes in the renal cortex. Compared with the controls, urinary NAG, ALP activities, and the levels of GSH, MDA, and the activities of PKC, Na⁺–K⁺-ATPase, and Ca²⁺-ATPase in rats from the Cd-treated group were significantly increased. SOD activity was suppressed by Cd. Urinary NAG activity and the level of GSH and the activities of PKC and Ca²⁺-ATPase in both CPZ and Ver pre-treated groups were significantly lower than that in Cd-treated rats. The present results showed that Cd-induced kidney damage was related to the oxidative damage and disturb intracellular Ca²⁺ homeostasis. Both CPZ and Ver possess some ability to prevent cadmium-induced kidney damage via antioxidative action and by maintaining calcium homeostasis.     

Ca2+-activated force-generating properties of mammalian skeletal muscle fibres: histochemically identified single peeled rabbit fibres

Summary Single peeled (sarcolemma removed) rabbit skeletal muscle fibres, identified histochemically from their myofibrillar ATPase and oxidative staining pattterns, were characterized according to their Ca²⁺-activated steady-state force-generating properties at normal intracellular pH (7.0) and under acidotic (pH 6.5) conditions. Maximum force-generating capacity of each fibre was assessed by measuring steady-state isometric force generation at saturating Ca²⁺ concentration at both pH values. The Ca²⁺ sensitivity of each fibre was ascertained by determining the percentage of maximum force generated at each of several subsaturating Ca²⁺ concentrations at both pH values. Fibres were selected from soleus, tibialis anterior and adductor magnus muscles. At subsaturating Ca²⁺ concentrations only two functional groups of fibres were distinguishable, corresponding to the histochemical classifications type I and type II. Type I fibres were more sensitive to Ca²⁺ and less depressed by acidosis than type II fibres in the subsaturating range of Ca²⁺ concentrations. At saturating Ca²⁺ concentrations, the acidotic depression of maximum force was significantly less for type I fibres than type II nonoxidative fibres regardless of their muscle of origin. Type II oxidative fibre maximum force properties depended upon the muscle of origin and demonstrated subgroups of these fibres that were different from type II nonoxidative fibres and similar to type I fibres.     

Excitation‐induced Ca2+ influx and skeletal muscle cell damage

Excessive exercise may lead to skeletal muscle cell damage with degradation of cellular components and leakage of intracellular enzymes. Calcium has repeatedly been proposed to be involved in these processes. Studies have shown that the resting level of cytoplasmic Ca²⁺ increases up to threefold during long‐term low‐frequency stimulation. We have shown that electrical stimulation produces a marked increase in Ca²⁺ uptake and Ca²⁺ content in rat skeletal muscle, both in vivo and in vitro. Continuous stimulation for 240 min at 1 Hz results in an increased release (18‐fold) of lactate dehydrogenase (LDH) from extensor digitorum longus (EDL) muscle. This was associated with an increased total Ca²⁺ content (185%), was augmented at high [Ca²⁺]_o and suppressed at low [Ca²⁺]_o. The release of LDH may reflect partial loss of sarcolemmal integrity as a result of degradation of membrane components by Ca²⁺‐activated enzymes (e.g. calpain or phospholipase A₂). After cessation of stimulation the increased release of LDH continues for at least 120 min. This is associated with an up to sevenfold increase in ⁴⁵Ca uptake. The increased permeability to Ca²⁺ may further activate calpain and phospholipase A₂ and accelerate the loss of membrane integrity. Stimulation‐induced uptake of Ca²⁺ and release of LDH is most pronounced in EDL (mainly composed of fast‐twitch fibres at variance with soleus which is mainly composed of slow‐twitch fibres). This may account for the observation that prolonged exercise leads to preferential damage to fast‐twitch fibres. We hypothesize that excessive exercise may lead to an intracellular accumulation of Ca²⁺ and increased cytoplasmic Ca²⁺ causing activation of self‐accelerating degradative pathways leading to muscle damage.     

Differences in α2-adrenoceptor modulation of calcium channels in vascular smooth muscle cells of male and female rats

 Effects of the α₂-adrenergic agonist clonidine on current through Ca²⁺ channels was recorded from vascular smooth muscle cells isolated from tail arteries and aortae of male and female rats. The average Ba²⁺ current in control was not significantly different between males and females; however, clonidine (1 μM) enhanced Ba²⁺ current through Ca²⁺ channels in cells from females, but not from males. The greater sensitivity of vascular smooth muscle cells to clonidine may underlie different contractile responses to α₂-adrenergic agonists between males and females. Received: 20 May 1996/Received after revision and accepted: 2 August 1996     

The role of Ca2+ and calmodulin in insulin signalling in mammalian skeletal muscle

The role of Ca²⁺ in mediating effects of insulin on skeletal muscle has been widely debated. It is believed that in skeletal muscle Ca²⁺ has a permissive role, necessary but not of prime importance in mediating the stimulatory actions of insulin. In this review, we present evidence that insulin causes a localized increase in the concentration of Ca²⁺. Specifically, insulin induces a rise in near‐membrane Ca²⁺ but not the bulk Ca²⁺ in the myoplasm. The rise in near‐membrane Ca²⁺ is because of an influx through channels that can be blocked by L‐type Ca²⁺ channel inhibitors. Calcium appears to exert some of its subsequent effects via calmodulin‐dependent processes as calmodulin inhibitors block the translocation of glucose transporters and other enzymes as well as the insulin‐stimulated increase in glucose transport.     

Role of Ca2+ mobilization and Ca2+ sensitization in 8-iso-PGF2α-induced contraction in airway smooth muscle

Background Isoprostanes are prostaglandin (PG)-like compounds synthesized by oxidative stress, not by cyclooxygenase, and increase in bronchoalveolar lavage fluid of patients with asthma. The airway inflammation implicated in this disease may be amplified by oxidants. Although isoprostanes are useful biomarkers for oxidative stress, the action of these agents on airways has not been fully elucidated. Objective This study was designed to determine the intracellular mechanisms underlying the effects of oxidative stress on airway smooth muscle, focused on Ca²⁺ signalling pathways involved in the effect of 8-iso-PGF_2α. Methods Using simultaneous recording of isometric tension and F₃₄₀/F₃₈₀ (an indicator of intracellular concentrations of Ca²⁺, [Ca²⁺]_i), we examined the correlation between tension and [Ca²⁺]_i in response to 8-iso-PGF_2α in the fura-2 loaded tracheal smooth muscle. Results Augmented tension and F₃₄₀/F₃₈₀ by 8-iso-PGF_2α were attenuated by ICI-192605, an antagonist of thromboxane A₂ receptors (TP receptors). Moreover, D609, an antagonist of phosphatidylcholine-specific phospholipase C, markedly reduced both the tension and F₃₄₀/F₃₈₀ induced by 8-iso-PGF_2α, whereas U73122, an antagonist of phosphatidylinositol-specific phospholipase C, modestly inhibited them by 8-iso-PGF_2α. SKF96365, a non-selective antagonist of Ca²⁺ channels, markedly reduced both tension and F₃₄₀/F₃₈₀ by 8-iso-PGF_2α. However, diltiazem and verapamil, voltage-dependent Ca²⁺ channel inhibitors, modestly attenuated tension although their reduction of F₃₄₀/F₃₈₀ was not different from that by SKF96365. Y-27632, an inhibitor of Rho-kinase, significantly attenuated contraction induced by 8-iso-PGF_2α without reducing F₃₄₀/F₃₈₀, whereas GF109203X and Go6983, protein kinase C inhibitors, did not markedly antagonize them although reducing F₃₄₀/F₃₈₀ with a potency similar to Y-27632. Conclusion 8-iso-PGF_2α causes airway smooth muscle contraction via activation of TP receptors. Ca²⁺ mobilization by SKF96365- and D609-sensitive Ca²⁺ influx and Ca²⁺ sensitization by Rho-kinase contribute to the intracellular mechanisms underlying the action of 8-iso-PGF_2α. Rho-kinase may be a therapeutic target for the physiologic abnormalities induced by oxidative stress in airways.     

The spectral changes in EMG during a second bout eccentric contraction could be due to adaptation in muscle fibres themselves: a simulation study

The mechanism of marked reduction in damage symptoms after repeated bout of similar eccentric contractions is still unknown. The neuronal adaptation leading to reduction of muscle fibre propagation velocity (MFPV) due to increased activation of slow-twitch motor units (MUs), decrease in activation of fast-twitch MUs, and/or increase in MU synchronization was suggested as a cause for lower EMG frequency characteristics. However, the repeated bout effect could occur also after electrically stimulated exercise. Prolonged elevation of cytoplasmic Ca²⁺ due to the increased membrane permeability after eccentric contractions was reported. Elevated Ca²⁺ induced peripheral changes that included alteration of intracellular action potential and MFPV reduction. We simulated and compared changes in EMG frequency characteristics related to effects of central nervous system (CNS) or to peripheral changes. The simulations were performed for different electrode arrangements and positions. The results showed that the peripheral effects could be similar or even stronger than the effects related to CNS. We hypothesised that the repeated bout effect was a consequence of the adaptation in muscle fibres necessary for avoiding Ca²⁺-induced protein and lipid degradation due to Ca²⁺ overload resulting from the increased membrane permeability after eccentric contraction. The possibilities for noninvasive testing of this hypothesis were discussed.     

Ruthenium red reduces the Ca2+ sensitivity of Ca2+ uptake into cardiac sarcoplasmic reticulum

 Ruthenium red inhibits mitochondrial Ca²⁺ uptake and is widely used as an inhibitor of ryanodine-sensitive Ca²⁺ channels that function to release Ca²⁺ from the sarcoplasmic reticulum (SR) of muscle cells. It also has effects on other Ca²⁺ channels and ion transporters. To study the effects of ruthenium red on Ca²⁺ transport into the SR of cardiac muscle cells, fluorescence measurements of Ca²⁺ uptake into cardiac SR vesicles were made. Ruthenium red significantly decreased the Ca²⁺ sensitivity of SR uptake in a dose-dependent manner at concentrations ranging from 5 μM to 20 μM. There were no significant effects of ruthenium red on the maximum velocity or the Hill coefficient of SR Ca²⁺ uptake. Received: 14 January 1998 / Received after revision: 12 March 1998 / Accepted: 16 March 1998     

Biochemical events associated with PHA-induced lymphocyte activation in human ageing II. Characteristics of the early Ca2+ uptake

Since the early biochemical changes are critical in defining the triggering mechanism of a mitogen-induced lymphocyte activation, their study could provide a good understanding of the processes that might be relevant to the immune deficiency associated with ageing.The increase of Ca²⁺ influx appears to be one of these earliest events which takes place in the first minutes following the contact with stimulating agents, as a consequence of membrane activation. Therefore, the timing and the magnitude of Ca²⁺ influx were analyzed in unstimulated and PHA-stimulated peripheral blood lymphocytes (PBL) from old and adult subjects.Whereas PBL from elders exhibited a decrease in DNA synthesis, the characteristics of Ca²⁺ accumulation into unstimulated and PHA-stimulated PBL were found unaltered in the elderly.The data support the evidence that the cellular defect relevant to the depressed response to T-mitogens associated with ageing, does not result from the defect of Ca²⁺ transport induced by membrane activation.     

The effect of praziquantel on calcium in Hymenolepis diminuta

Praziquantel (PZ) at concentrations down to 5 × 10^?8 M induced a rapid contraction of Hymenolepis diminuta musculature. This effect was accompanied by a strong inhibition of ⁴⁵Ca²⁺ incorporation which showed some dependence on Ca²⁺ concentration. Ca²⁺ efflux experiments showed that PZ markedly stimulated the release of Ca²⁺ from tapeworms preloaded with ⁴⁵Ca²⁺, with the effluxed Ca²⁺ being derived from a small fast pool and a larger slow pool. This stimulatory effect appeared, like PZ-induced muscle contraction, to be independent of external Ca²⁺. By carrying out ⁴⁵Ca²⁺ exchange experiments under near equilibrium conditions and atomic absorption spectroscopy it could be demonstrated that PZ resulted in a net excretion of endogenous Ca²⁺. In PZ-induced contracted worms adenylate nucleotide levels and the adenylate energy charge were not significantly different from those of untreated control worms. Also, PZ had no effect on Ca²⁺-stimulated ATPase activity of the tapeworm's tegumental brush border. Nor did the drug alter the activities of Ca²⁺-ATPases in whole homogenates of worms or mitochondria, microsomal or soluble fractions. Although the mechanism of PZ-induced changes in Ca²⁺ transport was not elucidated, it is suggested that the sustained release of endogenous Ca²⁺ may affect the sequence of excitation-contraction coupling and that such interference may cause the observed massive contraction of the tapeworm's musculature.     

The elusive role of store depletion in the control of intracellular calcium release

The contractile cycle of striated muscles, skeletal and cardiac, is controlled by a cytosolic [Ca²⁺] transient that requires rapid movements of the ion through channels in the sarcoplasmic reticulum (SR). A functional signature of these channels is their closure after a stereotyped time lapse of Ca²⁺ release. In cardiac muscle there is abundant evidence that termination of release is mediated by depletion of the Ca²⁺ store, even if the linkage mechanism remains unknown. By contrast, in skeletal muscle the mechanisms of release termination are not understood. This article reviews measurements of store depletion, the experimental evidence for dependence of Ca²⁺ release on the [Ca²⁺] level inside the SR, as well as tests of the molecular nature of putative intra-store Ca²⁺ sensors. Because Ca²⁺ sparks exhibit the basic release termination mechanism, much attention is dedicated to the studies of store depletion caused by sparks and its relationship with termination of sparks. The review notes the striking differences in volume, content and buffering power of the stores in cardiac vs. skeletal muscle, differences that explain why functional depletion is much greater for cardiac than skeletal muscle stores. Because in skeletal muscle store depletion is minimal and reduction in store [Ca²⁺] does not appear to greatly inhibit Ca²⁺ release, it is concluded that decrease in free SR [Ca²⁺] does not mediate physiological termination of Ca²⁺ release in this type of muscle. In spite of the apparent absence of store depletion and its putative channel closing effect, termination of Ca²⁺ sparks is faster and more robust in skeletal than cardiac muscle. A gating role of a hypothetical “proximate store” constituted by polymers of calsequestrin and associated proteins is invoked in an attempt to preserve a role for store depletion and unify mechanisms in both types of striated muscle.     

Characterization of Ca2+- and Sr2+-activated tension in functionally skinned chicken fibers of normal and dystrophic skeletal and normal cardiac muscle

The Ca²⁺ and Sr²⁺ activation of tension in functionally skinned chicken fibers of normal and dystrophic skeletal and normal cardiac muscle were studied. The muscles studied can be separated into two groups based upon their Ca²⁺ and Sr²⁺ sensitivities: those which are significantly more sensitive to Ca²⁺ than to Sr²⁺, pectoralis and posterior latissimus dorsi (PLD), and those which show no Ca²⁺/Sr²⁺ sensitivity difference, cardiac and anterior latissimus dorsi (ALD). This suggests that there is more than one type of Ca²⁺ site involved in Ca²⁺ control of muscle contraction in different muscle types and suggests that ALD and cardiac muscle may be controlled by a different type of binding site than PLD and pectoralis muscle. Dystrophic ALD and PLD muscles showed little change in their Ca²⁺ and Sr²⁺ sensitivities from those of normal muscles in contrast to the pectoralis which showed a decrease in both Ca²⁺ and Sr²⁺ sensitivity (approaching that of PLD) with the onset of dystrophy. Similarly, upon SDS polyacrylamide gel electrophoresis, dystrophic ALD and PLD muscles showed no difference in contractile proteins from those of normal muscles, in contrast to pectoralis muscle where the appearance of a 36,000 dalton protein band correlated with the onset of dystrophy and the changes in the Ca²⁺/Sr²⁺ activation properties of this muscle. The contractile protein band pattern of normal and dystrophic PLD and dystrophic pectoralis muscle were similar including the presence of the 36,000 dalton protein.     

Altered Ca2+ sparks in aging skeletal and cardiac muscle

Ca²⁺ sparks are the fundamental units that comprise Ca²⁺-induced Ca²⁺ release (CICR) in striated muscle cells. In cardiac muscle, spontaneous Ca²⁺ sparks underlie the rhythmic CICR activity during heart contraction. In skeletal muscle, Ca²⁺ sparks remain quiescent during the resting state and are activated in a plastic fashion to accommodate various levels of stress. With aging, the plastic Ca²⁺ spark signal becomes static in skeletal muscle, whereas loss of CICR control leads to leaky Ca²⁺ spark activity in aged cardiomyocytes. Ca²⁺ spark responses reflect the integrated function of the intracellular Ca²⁺ regulatory machinery centered around the triad or dyad junctional complexes of striated muscles, which harbor the principal molecular players of excitation-contraction coupling. This review highlights the contribution of age-related modification of the Ca²⁺ release machinery and the effect of membrane structure and membrane cross-talk on the altered Ca²⁺ spark signaling during aging of striated muscles.     

The role of SERCA2a/PLN complex, Ca2+ homeostasis, and anti-apoptotic proteins in determining cell fate

Intracellular calcium is a major coordinator of numerous aspects of cellular physiology, including muscle contractility and cell survival. In cardiac muscle, aberrant Ca²⁺ cycling has been implicated in a range of pathological conditions including cardiomyopathies and heart failure. The sarco(endo)plasmic reticulum Ca²⁺ transport adenosine triphosphatase (SERCA2a) and its regulator phospholamban (PLN) have a central role in modulating Ca²⁺ homeostasis and, therefore, cardiac function. Herein, we discuss the mechanisms through which SERCA2a and PLN control cardiomyocyte function in health and disease. Emphasis is placed on our newly identified PLN-binding partner HS-1-associated protein X-1 (HAX-1), which has an anti-apoptotic function and presents with numerous similarities to Bcl-2. Recent evidence indicates that proteins of the Bcl-2 family can influence ER Ca²⁺ content, a critical determinant of cellular sensitivity to apoptosis. The discovery of the PLN/HAX-1 interaction therefore unveils an important new link between Ca²⁺ homeostasis and cell survival, with significant therapeutic potential.     

钙激活性氯离子通道与高肺血流性肺动脉高压

Pulmonary hypertension induced by high pulmonary blood flow involves a variety of complex mechanisms, including endothelial damage, pulmonary artery smooth muscle relaxation-contraction disorder and vascular remodeling. Besides, the factor of ion channels in pulmonary artery smooth muscle cells is also highly correlated to vasoconstriction. In recent years, many studies have shown that activation of Ca²⁺-activated Cl^- channels is responsible for the membrane depolarization of pulmonary artery smooth muscle cells, and plays an important role in the regulation of vascular tone and vasoconstriction. This article reviews the biophysical and pharmacological characteristics of Ca²⁺-activated Cl^- channels as well as the influence of Ca²⁺-activated Cl^- channels in high pulmonary blood flow-induced pulmonary hypertension.