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.     

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   

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 [mu]m 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 <= 0.05).     

Comparison of Volatile Anesthetic Actions on Intracellular Calcium Stores of Vascular Smooth Muscle: Investigation in Isolated Systemic Resistance Arteries

Background: Volatile anesthetic actions on intracellular Ca2+ stores (i.e., sarcoplasmic reticulum [SR]) of vascular smooth muscle have not been fully elucidated.

Methods: Using isometric force recording method and fura-2 fluorometry, the actions of four volatile anesthetics on SR were studied in isolated endothelium-denuded rat mesenteric arteries.

Results: Halothane (>= 3%) and enflurane (>= 3%), but not isoflurane and sevoflurane, increased the intracellular Ca2+ concentration ([Ca2+]i) in Ca2+-free solution. These Ca2+-releasing actions were eliminated by procaine. When each anesthetic was applied during Ca2+ loading, halothane (>= 3%) and enflurane (5%), but not isoflurane and sevoflurane, decreased the amount of Ca2+ in the SR. However, if halothane or enflurane was applied with procaine during Ca2+ loading, both anesthetics increased the amount of Ca2+ in the SR. The caffeine-induced increase in [Ca2+]i was enhanced in the presence of halothane (>= 1%), enflurane (>= 1%), and isoflurane (>= 3%) but was attenuated in the presence of sevoflurane (>= 3%). The norepinephrine-induced increase in [Ca2+]i was enhanced only in the presence of sevoflurane (>= 3%). Not all of these anesthetic effects on the [Ca2+]i were parallel with the simultaneously observed anesthetic effects on the force.     

Comparison of volatile anesthetic actions on intracellular calcium stores of vascular smooth muscle: investigation in isolated systemic resistance arteries

BACKGROUND: Volatile anesthetic actions on intracellular Ca2+ stores (ie., sarcoplasmic reticulum [SR]) of vascular smooth muscle have not been fully elucidated. METHODS: Using isometric force recording method and fura-2 fluorometry, the actions of four volatile anesthetics on SR were studied in isolated endothellum-denuded rat mesenteric arteries. RESULTS: Halothane (> or = 3%) and enflurane (> or = 3%), but not isoflurane and sevoflurane, increased the intracellular Ca2+ concentration ([Ca2+]i) in Ca2+-free solution. These Ca2+-releasing actions were eliminated by procaine. When each anesthetic was applied during Ca2+ loading, halothane (> or = 3%) and enflurane (5%), but not isoflurane and sevoflurane, decreased the amount of Ca2+ in the SR. However, if halothane or enflurane was applied with procaine during Ca2+ loading, both anesthetics increased the amount of Ca2+ in the SR. The caffeine-induced increase in [Ca2+], was enhanced in the presence of halothane (> or = 1%), enflurane (> or = 1%), and isoflurane (> or = 3%) but was attenuated in the presence of sevoflurane (> or = 3%). The norepinephrine-induced increase in [Ca2+], was enhanced only in the presence of sevoflurane (> or = 3%). Not all of these anesthetic effects on the [Ca2+]i were parallel with the simultaneously observed anesthetic effects on the force. CONCLUSIONS: In systemic resistance arteries, the halothane, enflurane, isoflurane, and sevoflurane differentially influence the SR functions. Both halothane and enflurane cause Ca2+ release from the caffeine-sensitive SR. In addition, both anesthetics appear to have a stimulating action on Ca2+ uptake in addition to the Ca2+-releasing action. Halothane, enflurane, and isoflurane all enhance, while sevoflurane attenuates, the Ca2+-induced Ca2+-release mechanism. However, only sevoflurane stimulates the inositol 1,4,5-triphosphate-induced Ca2+ release mechanism. Isoflurane and sevoflurane do not stimulate Ca2+ release or influence Ca2+ uptake.     

Differential Effects of Bupivacaine on Intracellular Ca2+ Regulation: Potential Mechanisms of Its Myotoxicity

Background: Bupivacaine produces skeletal muscle damage in clinical concentrations. It has been suggested that this may be caused by an increased intracellular level of [Ca2+]. Therefore, the aim of this study was to investigate direct intracellular effects of bupivacaine on Ca2+ release from the sarcoplasmic reticulum (SR), on Ca2+ uptake into the SR, and on Ca2+ sensitivity of the contractile proteins.

Methods: Saponin skinned muscle fibers from the extensor digitorum longus muscle of BALB/c mice were examined according to a standardized procedure described previously. For the assessment of effects on Ca2+ uptake and release from the SR, bupivacaine was added to the loading solution and the release solution, respectively. Force transients and force decays were monitored, and the position of the curve relating relative isometric force versus free [Ca2+] was evaluated in the presence or absence of bupivacaine.

Results: Bupivacaine induces Ca2+ release from the SR. In addition, the Ca2+ loading procedure is suppressed, resulting in smaller caffeine-induced force transients after loading in the presence of bupivacaine. The decay of caffeine-induced force transients is reduced by bupivacaine, and it also shifts [Ca2+]-force relation toward lower [Ca2+].     

The Action of Sevoflurane on Vascular Smooth Muscle of Isolated Mesenteric Resistance Arteries (Part 2): Mechanisms of Endothelium-independent Vasorelaxation

Background: The precise mechanisms behind the direct inhibitory action of sevoflurane on vascular smooth muscle have not been fully elucidated.

Methods: Endothelium-denuded smooth muscle strips were prepared from rat small mesenteric arteries. Isometric force and intracellular Ca2+ concentration ([Ca2+]i) were measured simultaneously in the fura-2-loaded strips. In another series of experiments, only isometric force was measured in the [beta]-escin-membrane-permeabilized strips.

Results: Sevoflurane (3-5%) inhibited the increases in both the [Ca2+]i and the force induced by either norepinephrine (0.5-10 [mu]m) or 40 mm K+. Sevoflurane still inhibited the increase in [Ca2+]i induced by norepinephrine after depletion of intracellular Ca2+ stores with ionomycin, although it little influenced the increase in [Ca2+]i induced by norepinephrine after treatment with verapamil. In the fura-2-loaded membrane-intact muscle, sevoflurane caused a rightward shift of Ca2+-force relation during force development to stepwise increment of extracellular Ca2+ concentration during 40-mm K+ depolarization in either the presence or the absence of norepinephrine. In contrast, sevoflurane did not influence Ca2+-activated contraction in the [beta]-escin-permeabilized muscle, in which [alpha]-adrenergic receptor coupling was not retained.     

In Vitro Effects of Desflurane, Sevoflurane, Isoflurane, and Halothane in Isolated Human Right Atria

Background: Direct myocardial effects of volatile anesthetics have been studied in various animal species in vitro. This study evaluated the effects of equianesthetic concentrations of desflurane, sevoflurane, isoflurane, and halothane on contractile parameters of isolated human atria in vitro.

Methods: Human right atrial trabeculae, obtained from patients undergoing coronary bypass surgery, were studied in an oxygenated (95% O2-5% CO2) Tyrode's modified solution ([Ca2+]o = 2.0 mM, 30[degrees]C, stimulation frequency 0.5 Hz). The effects of equianesthetic concentrations (0.5, 1, 1.5, 2, and 2.5 minimum alveolar concentration [MAC]) of desflurane, sevoflurane, isoflurane, and halothane on inotropic and lusitropic parameters of isometric twitches were measured.

Results: Isoflurane, sevoflurane, and desflurane induced a moderate concentration-dependent decrease in active isometric force, which was significantly lower than that induced by halothane. In the presence of adrenoceptor blockade, the desflurane-induced decrease in peak of the positive force derivative and time to peak force became comparable to those induced by isoflurane. Halothane induced a concentration-dependent decrease in time to half-relaxation and a contraction-relaxation coupling parameter significantly greater than those induced by isoflurane, sevoflurane and desflurane.     

The action of sevoflurane on vascular smooth muscle of isolated mesenteric resistance arteries (part 2): mechanisms of endothelium-independent vasorelaxation

BACKGROUND: The precise mechanisms behind the direct inhibitory action of sevoflurane on vascular smooth muscle have not been fully elucidated. METHODS: Endothelium-denuded smooth muscle strips were prepared from rat small mesenteric arteries. Isometric force and intracellular Ca2+ concentration ([Ca2+]i) were measured simultaneously in the fura-2-loaded strips. In another series of experiments, only isometric force was measured in the beta-escin-membrane-permeabilized strips. RESULTS: Sevoflurane (3-5%) inhibited the increases in both the [Ca2+]i and the force induced by either norepinephrine (0.5-10 microm) or 40 mm K+. Sevoflurane still inhibited the increase in [Ca2+]i induced by norepinephrine after depletion of intracellular Ca2+ stores with ionomycin, although it little influenced the increase in [Ca2+]i induced by norepinephrine after treatment with verapamil. In the fura-2-loaded membrane-intact muscle, sevoflurane caused a rightward shift of Ca2+-force relation during force development to stepwise increment of extracellular Ca2+ concentration during 40-mm K+ depolarization in either the presence or the absence of norepinephrine. In contrast, sevoflurane did not influence Ca2+-activated contraction in the beta-escin-permeabilized muscle, in which alpha-adrenergic receptor coupling was not retained. CONCLUSIONS: The inhibitory effects of sevoflurane on both norepinephrine- and potassium chloride (KCl)-induced contractions are caused by reduction of [Ca2+]i in vascular smooth muscle and inhibition of the myofilament Ca2+ sensitivity. The [Ca2+]i-reducing effect of sevoflurane observed in both the norepinephrine- and the K+-stimulated muscle is mainly caused by inhibition of voltage-gated Ca2+ influx. The inhibitory effect of sevoflurane on Ca2+ activation of contractile proteins seems to be mediated by the cell membrane or by some diffusible substances that are lost in the beta-escin-permeabilized cells.     

Differential effects of bupivacaine on intracellular Ca2+ regulation: potential mechanisms of its myotoxicity

BACKGROUND: Bupivacaine produces skeletal muscle damage in clinical concentrations. It has been suggested that this may be caused by an increased intracellular level of [Ca2+]. Therefore, the aim of this study was to investigate direct intracellular effects of bupivacaine on Ca2+ release from the sarcoplasmic reticulum (SR), on Ca2+ uptake into the SR, and on Ca2+ sensitivity of the contractile proteins. METHODS: Saponin skinned muscle fibers from the extensor digitorum longus muscle of BALB/c mice were examined according to a standardized procedure described previously. For the assessment of effects on Ca2+ uptake and release from the SR, bupivacaine was added to the loading solution and the release solution, respectively. Force transients and force decays were monitored, and the position of the curve relating relative isometric force free [Ca2+] was evaluated in the presence or absence of bupivacaine. RESULTS: Bupivacaine induces Ca2+ release from the SR. In addition, the Ca2+ loading procedure is suppressed, resulting in smaller caffeine-induced force transients after loading in the presence of bupivacaine. The decay of caffeine-induced force transients is reduced by bupivacaine, and it also shifts [Ca2+]-force relation toward lower [Ca2+]. CONCLUSIONS: These data reveal that bupivacaine does not only induce Ca2+ release from the SR, but also inhibits Ca2+ uptake by the SR, which is mainly regulated by SR Ca2+ adenosine triphosphatase activity. It also has a Ca2+ -sensitizing effect on the contractile proteins. These mechanisms result in increased intracellular [Ca2+] concentrations and may thus contribute to its pronounced skeletal muscle toxicity.     

Volatile Anesthetics Affect Calcium Mobilization in Bovine Endothelial Cells

Background: The site where volatile anesthetics inhibit endothelium-dependent, nitric oxide-mediated vasodilation is unclear. To determine whether anesthetics could limit endothelium-dependent nitric oxide production by inhibiting receptor-mediated increases in cytosolic Calcium2+, experiments were performed to see if the inhalational anesthetics halothane, isoflurane, and enflurane affect intracellular Calcium2+ ([Ca2+]i) transients induced by the agonists bradykinin and adenosine triphosphate in cultured bovine aortic endothelial cells.

Methods: Bovine aortic endothelial cells, which had been loaded with the fluorescent Calcium2+ indicator Fura-2, were added to medium preequilibrated with volatile anesthetic (1.25% and 2.5% for isoflurane, 1.755 and 3.5% for enflurane, and 0.75% and 1.5% for halothane). In Calcium2+ -containing medium, intracellular Calcium sup 2+ transients were elicited in response to bradykinin (10 nM and 1 micro Meter) or adenosine triphosphate (1 micro Meter and 100 micro Meter).

Results: Both bradykinin and adenosine triphosphate triggered a rapid rise to peak [Ca2+]i followed by a gradual decline to a plateau above the resting level. Although basal [Ca2+]i was unaltered by the anesthetics, both halothane and enflurane, in a dose-dependent manner, depressed the peak and plateau of the [Ca2+] sub i transient elicited by 10 nM bradykinin, whereas isoflurane had no effect. When [Ca2+]i transients were elicited by 1 micro Meter bradykinin, halothane (1% and 5%) did not alter peak and plateau levels. Halothane and enflurane also decreased [Ca2+]i transients evoked by 1 micro Meter and 100 micro Meter adenosine triphosphate, whereas isoflurane also had no effect in this setting.     

Halothane and isoflurane augment depolarization-induced cytosolic CA2+ transients and attenuate carbachol-stimulated CA2+ transients

BACKGROUND: Neuronal excitability is in part determined by Ca2+ availability that is controlled by regulatory mechanisms of cytosolic Ca2+ ([Ca2+]cyt). Alteration of any of those mechanisms by volatile anesthetics (VAs) may lead to a change in presynaptic transmission and postsynaptic excitability. Using a human neuroblastoma cell line, the effects of halothane and isoflurane on cytosolic Ca2+ concentration ([Ca2+]cyt) in response to K+ and carbachol stimulation were investigated. METHODS: Volatile anesthetic (0.05-1 mm) action on stimulated [Ca2+]cyt transients were monitored in suspensions of SH-SY5Y cells loaded with fura-2. Potassium chloride (KCl; 100 mm) was used to depolarize and activate Ca2+ entry through voltage-dependent calcium channels; 1 mm carbachol was used to activate muscarinic receptor-mediated inositol triphosphate (IP3)-dependent intracellular Ca2+ release. Sequential stimulations, KCl followed by carbachol and vice versa, were used to investigate interactions between intracellular Ca2+ stores. RESULTS: Halothane and isoflurane in clinically relevant concentrations enhanced the K+-evoked [Ca2+]cyt transient whether intracellular Ca2+ stores were full or partially depleted. In contrast, halothane and isoflurane reduced the carbachol-evoked [Ca2+]cyt transient when the intracellular Ca2+ stores were full but had no effect when the Ca2+ stores were partially depleted by KCl stimulation. CONCLUSIONS: Volatile anesthetics acted on sites that differently affect the K+- and carbachol-evoked [Ca2+]cyt transients. These data suggest the involvement of an intracellular Ca2+ translocation from the caffeine-sensitive Ca2+ store to the inositol triphosphate-sensitive Ca2+ store that was altered by halothane and isoflurane.     

Halothane alters control of intracellular Ca2+ mobilization in single rat ventricular myocytes.

In an attempt to understand the cellular mechanisms underlying volatile anesthetic-induced myocardial depression, halothane-induced negative inotropy was investigated in an animal model through continuous monitoring of intracellular Ca2+ concentration [( Ca2+]i) in rat ventricular myocytes loaded with fura-2. Single cells were stimulated with 15 mM caffeine or 15 mM extracellular K+ (K+O) or were paced by extracellular glass suction pipette electrode. With each stimulus modality, halothane (0.6-1.5%) caused a significant (P less than 0.05) and dose-dependent depression of the Ca2+ transient. Caffeine and electrically stimulated Ca2+ transients were reduced, in 1.5% halothane, to 35 +/- 14 and 42 +/- 8% of control, respectively. Resting or basal [Ca2+]i was unaffected by halothane. Halothane did not elicit spontaneous Ca2+ transients in these cells. Single cells stimulated by trains of electrical stimuli at 1.0, 1.5, and 2.0 Hz showed a change in [Ca2+]i from prestimulus levels to a stimulated baseline steady state that appeared to increase with stimulus frequency. Halothane at 0.7% increased the change in resting to stimulated baseline [Ca2+]i and depressed net transients (P less than 0.05) at 1.0 and 1.5 Hz. In contrast, 0.1 microM ryanodine depressed the Ca2+ transients in myocytes stimulated by trains of stimuli, but did not potentiate the change in stimulated baseline [Ca2+]i at any pacing rate. The results are consistent with the hypothesis that halothane reduces Ca2+i availability by causing a net loss of Ca2+ from the sarcoplasmic reticulum. The results from experiments using onset of pacing to induce a sudden increase in Ca2+i load in previously quiescent myocytes suggest that halothane may act to limit sarcoplasmic reticulum and/or sarcolemmal uptake/extrusion mechanisms, as compared to ryanodine, which depletes sarcoplasmic reticulum Ca2+ stores without affecting reuptake and extrusion.     

Mechanisms of direct inhibitory action of isoflurane on vascular smooth muscle of mesenteric resistance arteries

BACKGROUND: Isoflurane has been shown to directly inhibit vascular reactivity. However, less information is available regarding its underlying mechanisms in systemic resistance arteries. METHODS: Endothelium-denuded smooth muscle strips were prepared from rat mesenteric resistance arteries. Isometric force and intracellular Ca2+ concentration ([Ca2+]i) were measured simultaneously in the fura-2-loaded strips, whereas only the force was measured in the beta-escin membrane-permeabilized strips. RESULTS: Isoflurane (3-5%) inhibited the increases in both [Ca2+]i and force induced by either norepinephrine (0.5 microM) or KCl (40 mM). These inhibitions were similarly observed after depletion of intracellular Ca2+ stores by ryanodine. Regardless of the presence of ryanodine, after washout of isoflurane, its inhibition of the norepinephrine response (both [Ca2+]i and force) was significantly prolonged, whereas that of the KCl response was quickly restored. In the ryanodine-treated strips, the norepinephrine- and KCl-induced increases in [Ca2+]i were both eliminated by nifedipine, a voltage-gated Ca2+ channel blocker, whereas only the former was inhibited by niflumic acid, a Ca2+-activated Cl- channel blocker. Isoflurane caused a rightward shift of the Ca2+-force relation only in the fura-2-loaded strips but not in the beta-escin-permeabilized strips. CONCLUSIONS: In mesenteric resistance arteries, isoflurane depresses vascular smooth muscle reactivity by directly inhibiting both Ca2+ mobilization and myofilament Ca2+ sensitivity. Isoflurane inhibits both norepinephrine- and KCl-induced voltage-gated Ca2+ influx. During stimulation with norepinephrine, isoflurane may prevent activation of Ca2+-activated Cl- channels and thereby inhibit voltage-gated Ca2+ influx in a prolonged manner. The presence of the plasma membrane appears essential for its inhibition of the myofilament Ca2+ sensitivity.     

Halothane and Isoflurane Augment Depolarization-induced Cytosolic CA2+ Transients and Attenuate Carbachol-stimulated CA2+ Transients

Background: Neuronal excitability is in part determined by Ca2+ availability that is controlled by regulatory mechanisms of cytosolic Ca2+ ([Ca2+]cyt). Alteration of any of those mechanisms by volatile anesthetics (VAs) may lead to a change in presynaptic transmission and postsynaptic excitability. Using a human neuroblastoma cell line, the effects of halothane and isoflurane on cytosolic Ca2+ concentration ([Ca2+]cyt) in response to K+ and carbachol stimulation were investigated.

Methods: Volatile anesthetic (0.05-1 mm) action on stimulated [Ca2+]cyt transients were monitored in suspensions of SH-SY5Y cells loaded with fura-2. Potassium chloride (KCl; 100 mm) was used to depolarize and activate Ca2+ entry through voltage-dependent calcium channels; 1 mm carbachol was used to activate muscarinic receptor-mediated inositol triphosphate (IP3)-dependent intracellular Ca2+ release. Sequential stimulations, KCl followed by carbachol and vice versa, were used to investigate interactions between intracellular Ca2+ stores.

Results: Halothane and isoflurane in clinically relevant concentrations enhanced the K+-evoked [Ca2+]cyt transient whether intracellular Ca2+ stores were full or partially depleted. In contrast, halothane and isoflurane reduced the carbachol-evoked [Ca2+]cyt transient when the intracellular Ca2+ stores were full but had no effect when the Ca2+ stores were partially depleted by KCl stimulation.     

In vitro effects of desflurane, sevoflurane, isoflurane, and halothane in isolated human right atria

BACKGROUND: Direct myocardial effects of volatile anesthetics have been studied in various animal species in vitro. This study evaluated the effects of equianesthetic concentrations of desflurane, sevoflurane, isoflurane, and halothane on contractile parameters of isolated human atria in vitro. METHODS: Human right atrial trabeculae, obtained from patients undergoing coronary bypass surgery, were studied in an oxygenated (95% O2-5% CO2) Tyrode's modified solution ([Ca2+]o = 2.0 mM, 30 degrees C, stimulation frequency 0.5 Hz). The effects of equianesthetic concentrations (0.5, 1, 1.5, 2, and 2.5 minimum alveolar concentration [MAC]) of desflurane, sevoflurane, isoflurane, and halothane on inotropic and lusitropic parameters of isometric twitches were measured. RESULTS: Isoflurane, sevoflurane, and desflurane induced a moderate concentration-dependent decrease in active isometric force, which was significantly lower than that induced by halothane. In the presence of adrenoceptor blockade, the desflurane-induced decrease in peak of the positive force derivative and time to peak force became comparable to those induced by isoflurane. Halothane induced a concentration-dependent decrease in time to half-relaxation and a contraction-relaxation coupling parameter significantly greater than those induced by isoflurane, sevoflurane and desflurane. CONCLUSIONS: In isolated human atrial myocardium, desflurane, sevoflurane, and isoflurane induced a moderate concentration-dependent negative inotropic effect. The effect of desflurane on time to peak force and peak of the positive force derivative could be related to intramyocardial catecholamine release. At clinically relevant concentrations, desflurane, sevoflurane, and isoflurane did not modify isometric relaxation.     

Volatile Anesthetics Increase Intracellular Calcium in Cerebrocortical and Hippocampal Neurons

Background: An increase in intracellular calcium concentration ([Ca2+]i) in neurons has been proposed as an important effect of volatile anesthetics, because they alter signaling pathways that influence neurotransmission. However, the existing data for anesthetic-induced increases in [Ca2+]i conflict.

Methods: Changes in [Ca2+]i were measured using fura-2 fluorescence spectroscopy in rat cortical brain slices at 90, 185, 370, and 705 [micro sign]M isoflurane. To define the causes of an increase in [Ca2+]i, slices were studied in Ca2+-free medium, in the presence of Ca2+-channel blockers, and in the presence of the Ca2+-release inhibitor azumolene. The authors compared the effect of the volatile anesthetic with that of the nonanesthetic compound 1,2-dichlorohexafluorocyclobutane. Single-dose experiments in CA1 neurons in hippocampal slices with halothane (360 [micro sign]M) and in acutely dissociated CA1 neurons with halothane (360 [micro sign]M) and isoflurane (445 [micro sign]M) also were performed.

Results: Isoflurane at 0.5, 1, and 2 minimum alveolar concentrations increased basal [Ca2+]i in cortical slices in a dose-dependent manner (P < 0.05). This increase was not altered by Ca2+-channel blockers or Ca2+-free medium but was reduced 85% by azumolene. The nonanesthetic 1,2-dichlorohexafluorocyclobutane did not increase [Ca2+] (i). In dissociated CA1 neurons, isoflurane reversibly increased basal [Ca (2+)]i by 15 nM (P < 0.05). Halothane increased [Ca2+]i in dissociated CA1 neurons and CA1 neurons in hippocampal slices by approximately 30 nM (P < 0.05).     

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.     

Volatile anesthetics increase intracellular calcium in cerebrocortical and hippocampal neurons

BACKGROUND: An increase in intracellular calcium concentration ([Ca2+]i) in neurons has been proposed as an important effect of volatile anesthetics, because they alter signaling pathways that influence neurotransmission. However, the existing data for anesthetic-induced increases in [Ca2+]i conflict. METHODS: Changes in [Ca2+]i were measured using fura-2 fluorescence spectroscopy in rat cortical brain slices at 90, 185, 370, and 705 microM isoflurane. To define the causes of an increase in [Ca2+]i, slices were studied in Ca2+-free medium, in the presence of Ca2+-channel blockers, and in the presence of the Ca2+-release inhibitor azumolene. The authors compared the effect of the volatile anesthetic with that of the nonanesthetic compound 1,2-dichlorohexafluorocyclobutane. Single-dose experiments in CA1 neurons in hippocampal slices with halothane (360 microM) and in acutely dissociated CA1 neurons with halothane (360 microM) and isoflurane (445 microM) also were performed. RESULTS: Isoflurane at 0.5, 1, and 2 minimum alveolar concentrations increased basal [Ca2+]i in cortical slices in a dose-dependent manner (P < 0.05). This increase was not altered by Ca2+-channel blockers or Ca2+-free medium but was reduced 85% by azumolene. The nonanesthetic 1,2-dichlorohexafluorocyclobutane did not increase [Ca2+]i. In dissociated CA1 neurons, isoflurane reversibly increased basal [Ca2+]i by 15 nM (P < 0.05). Halothane increased [Ca2+]i in dissociated CA1 neurons and CA1 neurons in hippocampal slices by approximately 30 nM (P < 0.05). CONCLUSIONS: (1) Isoflurane and halothane reversibly increase [Ca2+]i in isolated neurons and in neurons within brain slices. (2) The increase in [Ca2+]i is caused primarily by release from intracellular stores. (3) Increases in [Ca2+]i occur with anesthetics but not with the nonanesthetic 1,2-dichlorohexafluorocyclobutane.     

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).