Ca2+ uptake and Ca2+ release by skeletal muscle sarcoplasmic reticulum: differing sensitivity to inhalational anesthetics

The effects of halothane, enflurane, and isoflurane were measured on two different mechanisms of Ca2+ regulation by isolated skeletal muscle sarcoplasmic reticulum (SR) membranes. A 100,000-dalton Ca2+-ATPase protein transports Ca2+ from outside to inside the SR membrane. At concentration ranges representing anesthetic levels of 0.06 to 2.3 times MAC, halothane, enflurane, and isoflurane each increased rate of Ca2+ uptake by SR. Each concentration of isoflurane produced a greater rate of Ca2+ uptake, whereas halothane and enflurane produced maximum stimulation of Ca2+ uptake at 1 and 1.6 times MAC, respectively. The second Ca2+ regulation mechanism studied was a Ca2+ release channel in the SR membrane. The release of Ca2+ via this mechanism requires a critical threshold Ca2+ load (nmol Ca2+/mg SR protein) for Ca2+-induced Ca2+ release to occur. Each anesthetic tested effectively lowered the critical Ca2+ load threshold for Ca2+ release, i.e., the Ca2+ channel was more readily induced to an open state in the presence of anesthetic. The concentrations of anesthetics having this effect on the putative Ca2+ channel were between 0.0026 and 0.078 MAC equivalents for each agent, and these concentrations are much lower than the anesthetic concentrations affecting Ca2+ uptake. These data show that in isolated skeletal muscle SR membranes a Ca2+ channel release function is altered at anesthetic concentrations far below those that change Ca2+ uptake function by a Ca2+-ATPase and below concentrations of the volatile agents producing clinical anesthesia. The Ca2+ channel effect may represent protein-anesthetic interaction, whereas the Ca2+-ATPase effect may occur by a generalized SR membrane perturbation by the anesthetics.     

Desflurane induces only minor Ca2+ release from the sarcoplasmic reticulum of mammalian skeletal muscle

BACKGROUND: Desflurane is a weaker trigger of malignant hyperthermia than is halothane. There are very few data of the pathophysiologic background of this observation. Therefore, the authors' aim was to investigate the direct effect of desflurane on calcium release in skinned skeletal muscle fibers. METHODS: For the measurements, single saponin-skinned muscle fiber preparations of BALB/c mice were used. For Ca2+ release experiments, liquid desflurane at 0.6 and 3.5 mm was applied to weakly calcium-buffered solutions with no added Ca2+. Desflurane was diluted in strongly Ca2+-buffered solutions, with [Ca2+] between 3.0 and 24.9 micrometer for [Ca2+]-force relations. Force transients were transformed into Ca2+ transients based on the individual [Ca2+]-force relations. As controls, 30 mm caffeine and equimolar sevoflurane were investigated in the same muscle fibers. RESULTS: At 3.5 mm, desflurane induced peak force transients of 8 +/- 4% (mean +/- SD) of maximal Ca2+-activated force (Tmax). These peak values were significantly smaller than those in the presence of 3.5 mm sevoflurane (24 +/- 10% of Tmax, P < 0.05), and 4 or 5 times smaller than previously reported Ca2+-release-induced force transients by equimolar halothane. Calculated peak Ca2+ transients derived from force transients and induced by 3.5 and 0.6 mm desflurane were significantly smaller than those induced by 30 mm caffeine. The [Ca2+]-force relation was shifted by desflurane, resulting in a Ca2+-sensitizing effect. The maximal Ca2+-activated force was significantly increased by 0.6 mm desflurane in comparison with the control, with no added substance (P 相似文献   

FK506 (tacrolimus) increases halothane-induced Ca2+ release from skeletal muscle sarcoplasmic reticulum

BACKGROUND: FK506 binding protein is closely associated with the sarcoplasmic reticulum ryanodine receptor-channel and can modulate its function. The ryanodine receptor is stabilized by its association with FK506 binding protein. The immunosuppressant drugs FK506 (tacrolimus) and rapamycin can promote dissociation of FK506 binding protein from the ryanodine receptor 1 and by this mechanism increase sensitivity of ryanodine receptor 1 to agonists such as caffeine. Furthermore, it was shown recently that treatment of normal human skeletal muscle with FK506 and rapamycin increased halothane-induced contracture. The authors investigated the effect of the immunosuppressants FK506 and rapamycin on halothane-induced Ca2+ release in skeletal muscle sarcoplasmic reticulum vesicles. METHODS: Skeletal muscle terminal cisterns were isolated from New Zealand White rabbits. Ca2+ uptake and release was monitored in skeletal muscle sarcoplasmic reticulum vesicles using the fluo-3 fluorescent technique. Western Blot analysis of FK506 binding protein was performed using standard protocol. RESULTS: The authors observed that treatment of skeletal muscle sarcoplasmic reticulum vesicles with FK506 and rapamycin enhances halothane-induced Ca2+ release by about five times. Furthermore, the Ca2+ release induced by halothane in the presence of FK506 was inhibited by several antagonists of the ryanodine receptor, such as ruthenium red, spermine, and Mg2+. CONCLUSION: Dissociation of FK506 binding protein from its binding site in skeletal muscle sarcoplasmic reticulum vesicles can modulate halothane-induced Ca2+ release through the ryanodine receptor. Data are discussed in relation to the role of the FK506 binding protein in modulating the effect of halothane on the ryanodine receptor and the development of malignant hyperthermia phenotype.     

Thiopental does not alter Ca2+ uptake by cardiac sarcoplasmic reticulum

The effect of thiopental on Ca2+ uptake by cardiac sarcoplasmic reticulum (SR) isolated from the rabbit was examined to clarify the role of the sarcoplasmic reticulum in the negative inotropic action of thiopental. Thiopental, from 0 to 378 microM, did not alter the rate of Ca2+ uptake by the SR. We also compared the ATP dependence of Ca2+ uptake in the presence and absence of 284 microM thiopental. The Km for ATP and the Vmax of Ca+ uptake were unaffected by thiopental. It is concluded that thiopental does not alter Ca2+ uptake by the SR and that the negative inotropic effects of thiopental occur at other sites in the myocardial cell.     

Mg2+ dependence of halothane-induced Ca2+ release from the sarcoplasmic reticulum in skeletal muscle from humans susceptible to malignant hyperthermia

BACKGROUND: Recent work suggests that impaired Mg(2+) regulation of the ryanodine receptor is a common feature of both pig and human malignant hyperthermia. Therefore, the influence of [Mg(2+)] on halothane-induced Ca(2+) release from the sarcoplasmic reticulum was studied in malignant hyperthermia-susceptible (MHS) or -nonsusceptible (MHN) muscle. METHODS: Vastus medialis fibers were mechanically skinned and perfused with solutions containing physiologic (1 mm) or reduced concentrations of free [Mg(2+)]. Sarcoplasmic reticulum Ca(2+) release was detected using fura-2 or fluo-3. RESULTS: In MHN fibers, 1 mm halothane consistently did not induce sarcoplasmic reticulum Ca(2+) release in the presence of 1 mm Mg(2+). It was necessary to increase the halothane concentration to 20 mm or greater before Ca release occurred. However, when [Mg(2+)] was reduced below 1 mm, halothane became an increasingly effective stimulus for Ca(2+) release; e.g., at 0.4 mm Mg(2+), 58% of MHN fibers responded to halothane. In MHS fibers, 1 mm halothane induced Ca(2+) release in 57% of MHS fibers at 1 mm Mg(2+). Reducing [Mg(2+)] increased the proportion of MHS fibers that responded to 1 mm halothane. Further experiments revealed differences in the characteristics of halothane-induced Ca(2+) release in MHS and MHN fibers: In MHN fibers, at 1 mm Mg(2+), halothane induced a diffuse increase in [Ca(2+)], which began at the periphery of the fiber and spread slowly inward. In MHS fibers, halothane induced a localized C(2+)a release, which then propagated along the fiber. However, propagated Ca(2+) release was observed in MHN fibers when halothane was applied at an Mg(2+) concentration of 0.4 mm or less. CONCLUSIONS: When Mg(2+) inhibition of the ryanodine receptor is reduced, the halothane sensitivity of MHN fibers and the characteristics of the Ca release process approach that of the MHS phenotype. In MHS fibers, reduced Mg(2+) inhibition of the ryanodine receptor would be expected to have a major influence on halothane sensitivity. The Mg dependence of the halothane response in MHN and MHS may have important clinical implications in circumstances where intracellular [Mg(2+)] deviates from normal physiologic concentrations.     

Differential effects of sevoflurane, isoflurane, and halothane on Ca2+ release from the sarcoplasmic reticulum of skeletal muscle.

BACKGROUND: Although malignant hyperthermia after application of sevoflurane has been reported, little is known about its action on intracellular calcium homeostasis of skeletal muscle. The authors compared the effect of sevoflurane with that of isoflurane and halothane on Ca2+ release of mammalian sarcoplasmic reticulum and applied a novel method to quantify Ca2+ turnover in permeabilized skeletal muscle fibers. METHODS: Liquid sevoflurane, isoflurane, and halothane at 0.6 mM, 3.5 mM, and 7.6 mm were diluted either in weakly calcium buffered solutions with no added Ca2+ (to monitor Ca2+ release) or in strongly Ca2+ buffered solutions with [Ca2+] values between 3 nM and 24.9 microm for [Ca+]-force relations. Measurements were taken on single saponin skinned muscle fiber preparations of BALB/c mice. Individual [Ca2+]force relations were characterized by the Ca2+ concentration at half-maximal force that indicates the sensitivity of the contractile proteins and by the steepness. Each force transient was transformed directly into a Ca2+ transient with respect to the individual [Ca2+]-force relation of the fiber. RESULTS: At 0.6 mM, single force transients induced by sevoflurane were lower compared with equimolar concentrations of isoflurane and halothane (P < 0.05). Similarly, calculated peak Ca2+ transients of sevoflurane were lower than those induced by equimolar halothane (P < 0.05). The Ca2+ concentrations at half maximal force were decreased after the addition of sevoflurane, isoflurane, and halothane in a concentration-dependent manner (P < 0.05). CONCLUSION: Whereas sevoflurane, isoflurane, and halothane similarly increase the Ca2+ sensitivity of the contractile apparatus in skeletal muscle fibers, 0.6 mM sevoflurane induces smaller Ca2+ releases from the sarcoplasmic reticulum than does equimolar halothane.     

Mg2+ dependence of Ca2+ release from the sarcoplasmic reticulum induced by sevoflurane or halothane in skeletal muscle from humans susceptible to malignant hyperthermia

Background. In normal resting muscle, cytosolic Mg²⁺ exertsa potent inhibitory influence on the sarcoplasmic reticulum(SR) Ca²⁺ release channel (ryanodine receptor, RyR1). ImpairedMg²⁺-regulation of RyR1 has been proposed as a causal factorin malignant hyperthermia (MH). The aim of this study was tocompare the effects of cytosolic Mg²⁺ on SR Ca²⁺ release inducedby halothane or sevoflurane in normal (MHN) and MH susceptible(MHS) human skeletal muscle fibres. Methods. Samples of vastus medialis muscle were obtained frompatients under investigation for MH susceptibility. Single fibreswere mechanically skinned and perfused with solutions mimickingthe intracellular milieu. Changes in [Ca²⁺]_i were detected usingfura-2 fluorescence after application of equimolar halothaneor sevoflurane. Results. In MHN fibres, concentrations of sevoflurane or halothaneas high as 10 mM typically failed to induce SR Ca²⁺ releaseat physiological free [Mg²⁺] (1 mM). However, when [Mg²⁺] wasdecreased to 0.4 mM, SR Ca²⁺ release occurred in 51% (16/33)and 6% (2/33) of MHN fibres after the addition of 1 mM halothaneor 1 mM sevoflurane, respectively. Further decreases in [Mg²⁺]increased the proportion of responsive fibres. In the presenceof 0.1 mM [Mg²⁺], Ca²⁺ release occurred in all fibres (33/33)after the introduction of 1 mM halothane or 1 mM sevoflurane.In MHS fibres, 1 mM halothane or 1 mM sevoflurane-induced Ca²⁺release in 54% (7/13) or 15% (2/13) of fibres, respectively,at 1 mM Mg²⁺. A decrease in [Mg²⁺] to 0.2 mM Mg²⁺ was sufficientto render 100% of MHS fibres (13/13) responsive to 1 mM halothaneor 1 mM sevoflurane. Conclusions. In both MHS and MHN fibres (i) halothane is a morepotent activator of SR Ca²⁺ release than sevoflurane and (ii)as with halothane, the efficacy of sevoflurane-induced SR Ca²⁺release exhibits a marked dependence on cytosolic [Mg²⁺]. Themarked potentiation of SR Ca²⁺ release after a moderate reductionin cytosolic [Mg²⁺] suggests that conditions which cause hypomagnesaemiawill increase the probability and possibly severity of an MHevent. Conversely, maintenance of a normal or slightly increasedcytosolic [Mg²⁺] may reduce the probability of MH.     

Sevoflurane modulation of Ca2+ regulation in skeletal muscle sarcoplasmic reticulum vesicles from young and mature rabbits

Introduction: Developmental differences in splice variants of the two key sarcoplasmic reticulum (SR) calcium regulatory proteins, ryanodine (RyR1), and sarcoendoplasmic reticulum calcium pump (SERCA1) have been linked to various neuromuscular disorders, but not malignant hyperthermia (MH). However, it is unclear whether an age‐related difference in volatile anesthetic‐mediated SR calcium function exists that could add to our current understanding of the clinical presentation of MH syndrome and provide insight into molecular mechanisms for general anesthesia that may have other physiologic and/or pathophysiologic significance. Therefore, the effects of sevoflurane on intracellular calcium regulation in isolated SR membrane vesicles from the skeletal muscle of healthy young rabbits were compared to their adult counterpart using an established in vitro model with the assumption that exposure to sevoflurane would elicit a weaker response in the young SR. Methods: Through dual wavelength spectroscopy of Ca²⁺: Arsenazo III difference absorbance, the effects of sevoflurane on SR Ca²⁺ uptake rate and release in heavy and light fraction SR membrane vesicles isolated from the white muscle of anesthetized, postweaned (age = 6 weeks, n = 5) and adult (age = 6 months, n = 5) male New Zealand rabbits were examined. Results: The adult group showed a 50% increase in Ca²⁺ uptake rate from control at both subclinical and clinically relevant anesthetic concentrations, whereas in the SR from the younger animals, Ca²⁺ uptake rate was not altered by any concentration of sevoflurane. The sensitivity of both the low and high affinity Ca²⁺‐binding sites on RyR1 was increased by sevoflurane to the same extent in the SR vesicles from the young and mature adult rabbits. Interestingly, a greater potency of sevoflurane for the high affinity‐binding site was identified, and this was independent of age. Conclusions: These findings suggest that the sensitivity of the SR to sevoflurane‐mediated Ca²⁺ uptake may be increased with maturity, while an analogous developmental effect on RyR1 is less probable. Nonetheless, this study shows for the first time that a potent inhalational agent such as sevoflurane can influence the high affinity SR calcium‐binding site by lowering the extraluminal concentration of calcium necessary to trigger calcium release. While this may not be of consequence when inhaled anesthetics are administered to normal children or adults, it may have life‐threatening consequences in carriers of RyR1 mutations.     

Effects of isoflurane, sevoflurane, and halothane on myofilament Ca2+ sensitivity and sarcoplasmic reticulum Ca2+ release in rat ventricular myocytes

BACKGROUND: The aim of this study was to describe and compare the effects of isoflurane, sevoflurane, and halothane at selected concentrations (i.e., concentrations that led to equivalent depression of the electrically evoked Ca2+ transient) on myofilament Ca2+ sensitivity, sarcoplasmic reticulum (SR) Ca2+ content, and the fraction of SR Ca2+ released during electrical stimulation (fractional release) in rat ventricular myocytes. METHODS: Single rat ventricular myocytes loaded with fura-2 were electrically stimulated at 1 Hz, and the Ca2+ transients and contractions were recorded optically. Cells were exposed to each anesthetic for 1 min. Changes in myofilament Ca2+ sensitivity were assessed by comparing the changes in the Ca2+ transient and contraction during exposure to anesthetic and low Ca2+. SR Ca2+ content was assessed by exposure to 20 mm caffeine. RESULTS: Isoflurane and halothane caused a depression of myofilament Ca2+ sensitivity, unlike sevoflurane, which had no effect on myofilament Ca2+ sensitivity. All three anesthetics decreased the electrically stimulated Ca2+ transient. SR Ca2+ content was reduced by both isoflurane and halothane but was unchanged by sevoflurane. Fractional release was reduced by both isoflurane and sevoflurane, but was unchanged by halothane. CONCLUSIONS: Depressed myofilament Ca2+ sensitivity contributes to the negative inotropic effects of isoflurane and halothane but not sevoflurane. The decrease in the Ca2+ transient is either responsible for or contributory to the negative inotropic effects of all three anesthetics and is either primarily the result of a decrease in fractional release (isoflurane and sevoflurane) or primarily the result of a decrease in SR Ca2+ content (halothane).     

Calcium-induced calcium release from the sarcoplasmic reticulum can be evaluated with a half-logistic function model in aequorin-injected cardiac muscles

Purpose  

Release of calcium (Ca²⁺) from the sarcoplasmic reticulum (SR) induced by Ca²⁺ influx through voltage-dependent sarcolemmal L-type Ca²⁺ channels (CICR) in cardiac muscle cells has been implicated as a potential target contributing to anesthetic-induced myocardial depression. In an earlier study, we found that (1) a half-logistic (h-L) function, which represents a half-curve of a sigmoid logistic function with a boundary at the inflection point, curve-fits the first half of the ascending phases of the isometric myocardial tension and isovolumic left ventricular (LV) pressure waveforms better than a mono-exponential (m-E) function and (2) the h-L time constants are useful as inotropic indices. We report here our investigation of the potential application of an h-L function to the analysis of the first half of the ascending phase of the Ca²⁺ transient curve (faCaT) that precedes and initiates myocardial contraction and the increase in LV pressure.     

家兔未成熟心肌摄钙功能的实验研究

目的：从亚细胞水平研究未成熟心肌缺血－再灌注损伤中肌浆网（Sarcoplasmic reticulum,SR)摄钙功能和mRNA的表达。方法：将18只幼兔和18只成年兔随机分为4组，进行离体心灌注。测定各组心功能、冠状动脉流出液血气，单细胞内游离钙离子浓度（[Ca^2 ]i)，肌浆网钙离子－三磷酸腺苷酶（Sarcoplasmic reticulum Ca^2 -adenosine triphosphatase,SR Ca^2 -ATPase)活性，肌浆网^45Ca^2 (SR^45Ca^2 )摄取，并用斑点杂交（dot blot)检测SR Ca^2 -ATPase mRNA表达。结果：缺血－再灌注后，成熟与未成熟心肌均发生钙超载（P＞0．05）。未成熟心肌SR Ca^2 -ATPase活性恢复率明显高于成熟心肌（P＜0．01），SR^45Ca^2 摄取恢复率高于成熟心肌（P＜0．05），SR Ca^2 - ATPase mRNA表达上调低于成熟心肌（P＜0．01）。结论：未成熟心肌缺血－再灌注损伤钙超载中，SR^45Ca^2 摄取功能不起主要作用。     

Halothane and isoflurane effects on Ca2+ fluxes of isolated myocardial sarcoplasmic reticulum.

To elucidate better the differential myocardial depressant actions of halogenated volatile anesthetics, anesthetic-induced changes in Ca2+ accumulation, release, and Ca-ATPase (Ca2+ pump) activity of isolated canine cardiac sarcoplasmic reticulum (SR) vesicles were examined. An initial crude microsomal fraction of homogenized canine ventricle was subfractionated on a discontinuous sucrose gradient after Ca2+ loading in the presence of phosphate. Junctional SR (JSR) enriched with terminal cisternae was identified by its content of an electrophoretically verified approximately 450-kDa protein, the Ca(2+)-release channel (CaRC). When the CaRC of JSR was blocked by 1 microM ruthenium red (RR), the rate of Ca2+ uptake increased 47% as measured spectrophotometrically using the Ca-sensitive dye antipyrylazo III. A second fraction was identified as primarily longitudinal SR (LSR) based on its trace content of 450-kDa protein and 11% increase of Ca2+ uptake with RR. Halothane (0.75-2.5%) or isoflurane (2.5-4%) decreased net Ca2+ accumulation rate by either LSR or JSR, and the decrease in uptake rate of JSR was only partially reversed by addition of 1 microM RR (27% increase for isoflurane, 7% increase for halothane). Both halothane and isoflurane increased JSR ATP consumption as measured by a coupled-enzyme assay. 45Ca2+ efflux from passively loaded SR vesicles was then determined to verify that the decreased net uptake rate was due to enhanced Ca2+ efflux from vesicles. Both anesthetics increased passive Ca2+ efflux from SR vesicles in which the CaRC was blocked by 10 microM RR as well as those in which Ca2+ release via the CaRC was activated by 10 microM Ca2+.(ABSTRACT TRUNCATED AT 250 WORDS)     

Energy interconversion by the sarcoplasmic reticulum Ca2+-ATPase: ATP hydrolysis, Ca2+ transport, ATP synthesis and heat production

The sarcoplasmic reticulum of skeletal muscle retains a membrane bound Ca2+-ATPase which is able to interconvert different forms of energy. A part of the chemical energy released during ATP hydrolysis is converted into heat and in the bibliography it is assumed that the amount of heat produced during the hydrolysis of an ATP molecule is always the same, as if the energy released during ATP cleavage were divided in two non-interchangeable parts: one would be converted into heat, and the other used for Ca2+ transport. Data obtained in our laboratory during the past three years indicate that the amount of heat released during the hydrolysis of ATP may vary between 7 and 32 Kcal/mol depending on whether or not a transmembrane Ca2+ gradient is formed across the sarcoplasmic reticulum membrane. Drugs such as heparin and dimethyl sulfoxide are able to modify the fraction of the chemical energy released during ATP hydrolysis which is used for Ca2+ transport and the fraction which is dissipated in the surrounding medium as heat.     

Thiopental induces contraction of rat aortic smooth muscle through Ca(2+) release from the sarcoplasmic reticulum

Little is known about the mechanism of thiopental-induced contraction in vascular smooth muscle. This study aimed to clarify this question by conducting isometric tension experiments and (45)Ca(2+) flux measurements in endothelium-denuded rat aortic rings. Thiopental induced a concentration-dependent contraction under basal tension. This contraction was enhanced when rings were precontracted with phenylephrine in the presence of verapamil. In Ca(2+)-free solution, thiopental-induced contraction was reduced but not abolished with high concentrations. Ca(2+) store depletion with a maximum dose of caffeine in Ca(2+)-free solution further reduced the contraction by subsequent thiopental. Ca(2+) store depletion with thapsigargin completely abolished contraction by thiopental. (45)Ca(2+) influx experiment in the presence of verapamil showed that thiopental could not induce any Ca(2+) influx with or without phenylephrine prestimulation. The (45)Ca(2+) efflux experiment showed more evidence of thiopental-induced Ca(2+) release, which was abolished by thapsigargin. In conclusion, thiopental induces contraction in rat aortic smooth muscle by releasing Ca(2+) from the sarcoplasmic reticulum without Ca(2+) influx. IMPLICATIONS: This is the first study providing evidence that thiopental-induced vascular contraction is caused by Ca(2+) release from the sarcoplasmic reticulum of the smooth muscle.     

Depressed levels of Ca2+-cycling proteins may underlie sarcoplasmic reticulum dysfunction in the diabetic heart

In view of the depressed sarcoplasmic reticulum (SR) Ca2+-pump and Ca2+-release activities in the diabetic heart and the critical role of phosphorylation in regulating the SR function, we examined the status of Ca2+-calmodulin-dependent protein kinase (CaMK) and cAMP-dependent protein kinase (PKA)-mediated phosphorylations in the diabetic heart. Diabetes was induced in male Sprague-Dawley rats by an injection of streptozotocin (65 mg/kg i.v.), and the animals were killed 6 weeks later for assessment of the ventricular SR function. Depressed cardiac performance and SR Ca2+-uptake and -release activities in diabetic animals were accompanied by a significant decrease in the level of SR Ca2+-cycling proteins, such as ryanodine receptor, Ca2+-pump ATPase, and phospholamban. On the other hand, the CaMK- and PKA-mediated phosphorylations of these Ca2+-cycling proteins, the endogenous SR CaMK and PKA activities, and the endogenous SR and cytosolic phosphatase activities were increased in the diabetic heart. Treatment of 3-week diabetic animals with insulin partially or fully prevented the diabetes-induced changes in cardiac performance, SR Ca2+-uptake and -release activites, and SR protein content, whereas the diabetes-induced changes in SR CaMK- and PKA-mediated phosphorylations and activities, as well as phosphatase activities, were not significantly affected. These results suggest that the reduced content of the Ca2+-cycling proteins, unlike alterations in PKA and phosphatase activities, appear to be the major defect underlying SR dysfunction in the diabetic heart.     

The effect of the prostaglandin derivative PGBx on calcium uptake and release by skeletal muscle sarcoplasmic reticulum

The effects of the prostaglandin derivative PGBx on calcium release and uptake by skeletal muscle sarcoplasmic reticulum (SR) and on (Ca2+ + Mg2+)- adenosine triphosphatase (ATPase) activity were studied using skeletal muscle from rabbit hind legs. Both calcium uptake and Ca2+-ATPase activity were significantly inhibited by PGBx. Addition of PGBx to SR vesicles resulted in the release of calcium. It is proposed that this action of PGBx could be effected by the inhibition of ATPase and resulting passive release of calcium. The possibility also exists that PGBx could decrease the capacity of the SR vesicles for calcium in addition to any possible ionophoretic properties.     

Differential effects of bupivacaine and ropivacaine enantiomers on intracellular Ca2+ regulation in murine skeletal muscle fibers

BACKGROUND: Increased intracellular Ca concentrations are considered to be a major pathomechanism in local anesthetic myotoxicity. Racemic bupivacaine and S-ropivacaine cause Ca release from the sarcoplasmic reticulum of skeletal muscle fibers and simultaneously inhibit Ca reuptake. Examining the optical isomers of both agents, the authors investigated stereoselective effects on muscular Ca regulation to get a closer insight in subcellular mechanisms of local anesthetic myotoxicity. METHODS: R- and S-enantiomers as well as racemic mixtures of both agents were tested in concentrations of 1, 5, 10, and 15 mm. Saponin-skinned muscle fibers from the extensor digitorum longus muscle of BALB/c mice were examined according to a standardized procedure. For the assessment of effects on Ca uptake and release from the sarcoplasmic reticulum, agents were added to the loading solution and the release solution, respectively, and force and Ca transients were monitored. RESULTS: The effects of S-enantiomers on both Ca release and reuptake were significantly more pronounced than those of racemic mixtures and R-enantiomers, respectively. In addition, the effects of racemates were markedly stronger than those of R-enantiomers. With regard to Ca release, the effects of bupivacaine isomers were more pronounced than the isomers of ropivacaine. CONCLUSIONS: These data show that stereoselectivity is involved in alterations of intracellular Ca regulation by bupivacaine and ropivacaine. S-enantiomers seem to be more potent than R-enantiomers, with intermediate effects of racemic mixtures. In addition, lipophilicity also seems to determine the extent of Ca release by local anesthetics.     

七氟醚对豚鼠耳蜗外毛细胞Ca2+跨膜内流和内质网钙释放功能的影响

目的 观察七氟醚对豚鼠耳蜗外毛细胞Ca2+跨膜内流和内质网钙释放功能的影响,探讨其对听觉外周感受器(耳蜗)作用的可能机制.方法 第一部分成年豚鼠,雌雄不拘,迅速断头,取耳蜗,酶孵育后,机械分离法分离外毛细胞,30个活力良好的外毛细胞随机分为3组(n=10):对照组(C组),低浓度七氟醚组(S1组)和高浓度七氟醚组(S2组),用Fluo-3AM钙荧光指示剂染色后,分别给予纯氧、1.7%七氟醚、3.4%七氟醚处理20min,然后加入40mmol/L氯化钾,测定细胞内游离钙离子浓度([Ca2+];).第二部分以20 mmol/L 咖啡因代替氯化钾其余处理及分组同第一部分.结果 第一部分与基础值比较,各组给予七氟醚后[Ca2+];差异无统计学意义(P＞0.05),加入氯化钾后[Ca2+];升高(P＜0.01);S1组和S2组加入氯化钾后[Ca2+];低于C组,且S2组低于S1组(P＜0.05).第二部分与基础值比较,各组给予七氟醚后[Ca2+];差异无统计学意义(P＞0.05),加入咖啡因后[Ca2+];升高(P＜0.0);加入咖啡因后各组[Ca2+];差异无统计学意义(P＞0.05).结论 七氟醚可浓度依赖性地抑制豚鼠耳蜗外毛细胞电压依赖型Ca2+通道开放,而对内质网Ryanodine敏感性钙释放功能无影响.