The repolarizing effects of volatile anesthetics on porcine tracheal and bronchial smooth muscle cells.

This study was conducted to determine the effects of volatile anesthetics (potent bronchodilators) on membrane potentials in porcine tracheal and bronchial smooth muscle cells. We used a current-clamp technique to examine the effects of the volatile anesthetics isoflurane (1.5 minimum alveolar anesthetic concentration [MAC]) and sevoflurane (1.5 MAC) on membrane potentials of porcine tracheal and bronchial (third- to fifth-generation) smooth muscle cells depolarized by a muscarinic agonist, carbachol (1 microM). The effects of volatile anesthetics on muscarinic receptor binding affinity were also investigated by using a radiolabeled receptor assay technique. The volatile anesthetics isoflurane and sevoflurane induced significant repolarization of the depolarized cell membranes in the trachea (from -19.8 to -23.6 mV and to -24.8 mV, respectively) and bronchus (from -24.7 to -29.3 mV and -30.4 mV, respectively) without affecting carbachol binding affinity to the muscarinic receptor. The repolarizing effect was abolished by a Ca(2+)-activated Cl(-) channel blocker, niflumic acid. These results indicate that volatile anesthetic-induced repolarization of airway smooth muscle cell membranes might be caused by a change in Ca(2+)-activated Cl(-) channel activity and that the different repolarized effects of the volatile anesthetics could in part contribute to the different effects of volatile anesthetics on tracheal and bronchial smooth muscle contractions. IMPLICATIONS: By use of a current-clamp technique, the volatile anesthetics isoflurane and sevoflurane repolarized porcine airway smooth muscle cell membranes depolarized by a muscarinic agonist. This effect might be caused mainly by change in Ca(2+)-activated Cl(-) channel activity, not in K(+) channel activity.     

Interaction between volatile anesthetics and hypoxia in porcine tracheal smooth muscle

We investigated the direct interaction between the volatile anesthetics, isoflurane and sevoflurane, and hypoxia in porcine tracheal smooth muscle in vitro by simultaneously measuring muscle tension and intracellular concentration of free Ca(2+) ([Ca2+]i). Muscle tension was measured by using an isometric transducer, and [Ca2+]i was measured by using fura-2, an indicator of Ca2+. Under the condition of bubbling with 95% O2/5% CO2, [Ca2+]i was increased by 1 microM carbachol with a concomitant contraction. Volatile anesthetics significantly inhibited both carbachol-induced muscle contraction and increase in [Ca2+]i. Hypoxia bubbled with 95% N(2)/5% CO2 inhibited the muscle contraction by 30% with an increase in [Ca2+]i by 20%. Exposure to hypoxia substantially enhanced the inhibitory effects of these anesthetics on carbachol-induced muscle contraction, whereas the decreases in [Ca2+]i were significantly prevented by hypoxia. Under Ca2+-free conditions, hypoxia significantly decreased the muscle contraction by 20%; however, it still increased [Ca2+]i by 15%. Exposure to the anesthetics significantly enhanced the inhibitory effect of hypoxia on the muscle contraction; however, it appeared to have little effect on [Ca2+]i. Hypoxia inhibits airway smooth muscle contraction independently of intracellular Ca2+, and it substantially potentiates the inhibitory effects of volatile anesthetics on airway smooth muscle contraction. Implications: Hypoxia inhibits agonist-induced tracheal smooth muscle contraction with an increase in free Ca2+ [Ca2+]i, which comes from intracellular Ca2+ stores. Hypoxia also potentiates the inhibitory effect of volatile anesthetics on airway smooth muscle contraction. Conversely, there is a possibility that the treatment of asthmatic patients with oxygen partially attenuates the inhibitory effect of volatile anesthetics on airway smooth muscle contractility.     

Inhibitory effects of volatile anesthetics on K+ and Cl- channel currents in porcine tracheal and bronchial smooth muscle

BACKGROUND: K+ and Ca2+-activated Cl- (ClCa) channel currents have been shown to contribute to the alteration of membrane electrical activity in airway smooth muscle. This study was conducted to investigate the effects of volatile anesthetics, which are potent bronchodilators, on the activities of these channels in porcine tracheal and bronchial smooth muscles. METHODS: Whole-cell patch clamp recording techniques were used to investigate the effects of superfused isoflurane (0-1.5 minimum alveolar concentration) or sevoflurane (0-1.5 minimum alveolar concentration) on K+ and ClCa channel currents in dispersed smooth muscle cells. RESULTS: Isoflurane and sevoflurane inhibited whole-cell K+ currents to a greater degree in tracheal versus bronchial smooth muscle cells. More than 60% of the total K+ currents in tracheal smooth muscle appeared to be mediated through delayed rectifier K+ channels compared with less than 40% in bronchial smooth muscle. The inhibitory effects of the anesthetics were greater on the delayed rectifier K+ channels than on the remaining K+ channels. Cl- currents through ClCa channels were significantly inhibited by the anesthetics. The inhibitory potencies of the anesthetics on the ClCa channels were not different in tracheal and bronchial smooth muscle cells. CONCLUSIONS: Volatile anesthetics isoflurane and sevoflurane significantly inhibited Cl- currents through ClCa channels, and the inhibitory effect is consistent with the relaxant effect of volatile anesthetics in airway smooth muscle. Different distributions and different anesthetic sensitivities of K+ channel subtypes could play a role in the different inhibitory effects of the anesthetics on tracheal and bronchial smooth muscle contractions.     

Interactions of volatile anesthetics with neurodegenerative-disease-associated proteins

The prevalence of the neurodegenerative disorders is increasing as life expectancy lengthens, and there exists concern that environmental influences may contribute to this increase. These disorders are varied in their clinical presentation, but appear to have a common biophysical initiation. At this level, it is both plausible and now proven that anesthetics can enhance aggregation of some disease-causing proteins. Although data in support of an interaction in animal models are still lacking, data from clinical studies indicate an association, which provides further cause for concern. Many opportunities exist for rapid progress at all levels on defining whether anesthetics do indeed contribute to the pathogenesis of these progressive, debilitating disorders.     

Electromyographic detection of purinergic activity in Guinea pig detrusor smooth muscle

PURPOSE: We recorded nerve mediated extracellular electrical activity from guinea pig detrusor smooth muscle strips using suction electrodes and determined the electrophysiological origins of this signal and its relationship to contractile activity. MATERIALS AND METHODS: Mucosa-free detrusor strips were prepared from male guinea pigs sacrificed under Home Office license, physiologically superfused, attached to a pressure transducer and electrically stimulated (0.1 millisecond pulses). Electrical signals recorded using a bipolar reversible suction electrode were processed and recorded simultaneously with changes in strip tension. The effect of superfusion with alpha, beta-methylene adenosine triphosphate (ATP), atropine, extracellular [CaCl(2)] depletion and pharmacological Ca2+ channel blockade on the electrical and mechanical signals was determined. RESULTS: A biphasic electrical signal was consistently recorded from 37 detrusor strips. The signal was sensitive to graded reduction in [CaCl(2)] of the superfusate and abolished by tetrodotoxin in 7 preparations. The signal was also abolished in 12 preparations by alpha, beta-methylene ATP in association with an attenuated contraction but not significantly reduced in amplitude (p = 0.77) despite a significant reduction in tension with atropine (mean plus or minus SD 74% +/- 14% of control, p <0.001). The signal was attenuated to a mean maximum of 9% +/- 3% of control by pharmacological Ca2+ channel blockade and the remaining signal was abolished by alpha, beta-methylene ATP. CONCLUSIONS: The extracellular electrical signal recorded from guinea pig detrusor strips using suction electrodes originates from a purinergic mechanism. Although an atropine sensitive component may be present, the signal does not depend on cholinergic neuromuscular transmission and would not be expected to be generated by normal human detrusor. Provided that the electrophysiological basis of purinergic neurotransmission in guinea pig and human bladders is similar suction electrodes may be a valuable tool with which to evaluate in vitro and clinically by electromyography the pathological purinergic neuromuscular transmission that can be expressed in addition to normal cholinergic mechanisms in detrusor from dysfunctional human bladders.     

Cardioprotection with volatile anesthetics: mechanisms and clinical implications

Cardiac surgery and some noncardiac procedures are associated with a significant risk of perioperative cardiac morbid events. Experimental data indicate that clinical concentrations of volatile general anesthetics protect the myocardium from ischemia and reperfusion injury, as shown by decreased infarct size and a more rapid recovery of contractile function on reperfusion. These anesthetics may also mediate protective effects in other organs, such as the brain and kidney. Recently, a number of reports have indicated that these experimentally observed protective effects may also have clinical implications in cardiac surgery. However, the impact of the use of volatile anesthetics on outcome measures, such as postoperative mortality and recovery in cardiac and noncardiac surgery, is yet to be determined.     

Characterization of spontaneous depolarizations in smooth muscle cells of the Guinea pig prostate

PURPOSE: We characterized the electrical events recorded in small segments of the dorsal lobe of the prostate of immature male guinea pigs and examined some mechanisms underlying their generation. MATERIAL AND METHODS: Membrane potential recordings were made in the stroma of the guinea pig prostate using conventional single microelectrode techniques. RESULTS: Three distinct, spontaneously occurring electrical events were recorded in guinea pig prostate, namely slow waves, consisting of a depolarizing transient 14 mV in amplitude with 1 to 6 nifedipine sensitive spikes superimposed, pacemaker potentials, consisting of a larger depolarization 40 mV in amplitude, and STDs 1 to 10 mV in amplitude. Only spikes on slow waves were inhibited by nifedipine. The depolarizing transient of slow waves, pacemaker potentials and STDs were abolished by cyclopiazonic acid, a blocker of the SERCA pump, and the mitochondrial uncoupler cyanide m-chlorophenyl hydrazone as well as upon exposure to Ca(2+)-free saline or the Cl(-) channel blockers niflumic acid and anthracene-9-carboxylic acid (Sigma Chemical Co., St. Louis, Missouri). Examination of the stochastic properties of STDs revealed that they were not well modeled by Poisson statistics, but rather they occurred in a clustered manner, such they may well underlie pacemaker potential generation. CONCLUSIONS: Guinea pig prostate shows STD and pacemaker potentials that arise from the release of Ca(2+) from intracellular stores and the activation of Ca(2+) activated Cl(-) channels. We speculate that the depolarizing transient of prostatic slow waves is the propagated response of pacemaker potentials evoked at sites electrically distant from the recording electrode.     

Effects and interaction of verapamil and volatile anesthetics on the isolated perfused guinea pig heart

The direct cardiac effects of volatile anesthetics and calcium channel blockers are obscured in vivo by autonomic reflexes and other extrinsic influences. The authors examined the direct in vitro effects of verapamil and the volatile anesthetics, halothane (HAL), enflurane (ENF), and isoflurane (ISO), in the isolated guinea pig heart. Each heart (N = 36) was perfused at constant pressure with an oxygenated Krebs-Ringer solution at 36 degrees C. Recording electrodes were placed in the right atrium, septum, and right ventricular wall. Left ventricular pressure (LVP) and coronary flow were measured. The combination of 75 or 150 ng/ml verapamil and 0.7 or 1.4 minimum alveolar concentrations (MAC) of each of the three anesthetics dose-dependently depressed spontaneous atrial rate (HR) and peak LVP, and prolonged atrial-septal (AV) time and intraventricular conduction time (IVCT). ENF decreased HR and LVP and increased IVCT more than did HAL or ISO at each anesthetic level. The combination of either level of ENF and 150 ng/ml verapamil reduced HR more than did the same level of verapamil with HAL or ISO; 1.4 MAC ENF with 150 ng/ml verapamil also caused sinus arrest in 17% of hearts. Although ENF, HAL, and ISO alone similarly depressed AV time, 1.4 MAC ENF synergistically increased, and 1.4 HAL and ISO additively increased, the delay in AV time due to each level of verapamil. In addition, 1.4 MAC ENF caused significant 25% and 67% incidences of complete AV block with low and high verapamil levels, respectively. Both levels of ENF with verapamil also increased IVCT more than did HAL or ISO with verapamil.(ABSTRACT TRUNCATED AT 250 WORDS)     

异丙酚对离体人支气管平滑肌的作用

目的 观察异丙酚对离体人肺叶支气管平滑肌的作用。方法 离体人肺叶支气管取自胸外科肺叶切除术患者（n=10）,采用离体气管实验法,以乙酰胆碱（3μg·ml-1）激发,观察临床相关剂量的异丙酚（1、2、5、10、20μg·ml-1）对离体人肺叶支气管平滑肌的作用,脂肪乳剂作为对照。结果与对照组相比,1、2、5、10、20μg·ml-1的异丙酚显著减弱乙酰胆碱的平滑肌收缩反应（P值分别<0.05、<0.01、<0.01、<0.01、<0.01）。结论 临床相关剂量的异丙酚可有效地减弱乙酰胆碱介导的离体人肺叶支气管平滑肌的收缩反应.     

Effects of volatile anesthetics on store-operated Ca(2+) influx in airway smooth muscle

BACKGROUND: In airway smooth muscle (ASM), volatile anesthetics deplete sarcoplasmic reticulum (SR) Ca(2+) stores by increasing Ca(2+) "leak." Accordingly, SR replenishment becomes dependent on Ca(2+) influx. Depletion of SR Ca(2+) stores triggers Ca(2+) influx via specific plasma membrane channels, store-operated Ca(2+) channels (SOCC). We hypothesized that anesthetics inhibit SOCC triggered by increased SR Ca(2+) "leak," preventing SR replenishment and enhancing ASM relaxation. METHODS: In porcine ASM cells, SR Ca was depleted by cyclopiazonic acid or caffeine in 0 extracellular Ca(2+), nifedipine and KCl (preventing Ca(2+) influx through L-type and SOCC channels). Extracellular Ca(2+) was rapidly introduced to selectively activate SOCC. After SOCC activation, SR was replenished and the protocol repeated in the presence of 1 or 2 minimum alveolar concentration halothane, isoflurane, or sevoflurane. In other cells, characteristics of SOCC and interactions between acetylcholine (Ach) and volatile anesthetics were examined. RESULTS: Cyclopiazonic acid produced slow SR leak, whereas the caffeine response was transient in ASM cells. Reintroduction of extracellular Ca(2+) rapidly increased [Ca(2+)]i. This influx was insensitive to nifedipine, SKF-96365, and KBR-7943, inhibited by Ni and blockade of inositol 1,4,5-triphosphate-induced SR Ca(2+) release, and enhanced by ACh. Preexposure to 1 or 2 minimum alveolar concentration halothane completely inhibited Ca(2+) influx when extracellular Ca(2+) was reintroduced, whereas isoflurane and sevoflurane produced less inhibition. Only halothane and isoflurane inhibited ACh-induced augmentation of Ca(2+) influx. CONCLUSION: Volatile anesthetics inhibit a Ni/La-sensitive store-operated Ca(2+) influx mechanism in porcine ASM cells, which likely helps maintain anesthetic-induced bronchodilation.     

General anesthetics and vascular smooth muscle: direct actions of general anesthetics on cellular mechanisms regulating vascular tone

General anesthetics threaten cardiovascular stability by causing changes in cardiac function, vascular reactivity, and cardiovascular reflexes and significantly alter distribution of cardiac output to various organs. Their overall impact is often systemic hypotension, which is attributable to myocardial depression, peripheral vasodilation, and attenuated sympathetic nervous system activity. However, one could be more causative than the others, depending on anesthetic agents and cardiovascular factors inherent in patients (e.g., coexisting heart disease). It is generally believed that most general anesthetics attenuate sympathetic nervous system outflow from the central nervous system, thereby decreasing vascular resistance in peripheral circulations. Indeed, in previous in vivo studies, during administration of various general anesthetics, vascular resistance was decreased in most peripheral circulations; however, it was unaffected or increased in some peripheral circulations. General anesthetics may act directly on vascular smooth muscle and/or endothelial cells in various vascular beds, influencing total peripheral and/or regional vascular resistance, and hence organ blood flow. This article reviews previously reported direct (i.e., nonneural) vascular actions of general anesthetics and discusses their underlying mechanisms, their in vivo relevance, and the future of research for general anesthetic vascular pharmacology.     

Low-temperature modification of the inhibitory effects of volatile anesthetics on airway smooth muscle contraction in dogs

BACKGROUND: Because exposure to low temperature can modify the effect of volatile anesthetics on airway smooth muscle contraction, this study was conducted to investigate low-temperature modifications of the inhibitory effects of isoflurane and sevoflurane on canine tracheal smooth muscle tone by simultaneously measuring the muscle tension and intracellular concentration of Ca2+ ([Ca2+]i) and by measuring voltage-dependent Ca2+ channel activity. METHODS: [Ca2+]i was monitored by the 500-nm light emission ratio of preloaded fura-2, a Ca2+ indicator. Isometric tension was measured simultaneously. Whole cell patch clamp recording techniques were used to observe voltage-dependent Ca2+ channel activity in dispersed muscle cells. Isoflurane (0-3.0%) or sevoflurane (0-3%) was introduced to a bath solution at various temperatures (37, 34, or 31 degrees C). RESULTS: Low temperature (34 or 31 degrees C) reduced high-K+-induced (72.7 mm) muscle contraction and increased [Ca2+]i, but it enhanced carbachol-induced (1 microm) muscle contraction with a decrease in [Ca2+]i. The volatile anesthetics tested showed significant inhibition of both high-K+-induced and carbachol-induced airway smooth muscle contraction, with a concomitant decrease in [Ca2+]i. The inhibition of the carbachol-induced muscle contraction by volatile anesthetics was abolished partially by exposure to low temperature. Volatile anesthetics and low-temperature exposure significantly inhibited voltage-dependent Ca2+ channel activity of the smooth muscle. CONCLUSIONS: Exposure of airway smooth muscle to low temperature leads to an increase in agonist-induced muscle contractility, with a decrease in [Ca2+]i. The inhibition of voltage-dependent Ca2+ channel activity by exposure to low temperature and by volatile anesthetics cam be attributed, at least in part, to the decrease in [Ca2+]i.     

The nitric oxide pathway in pig isolated calyceal smooth muscle.

In pig and humans, whose kidneys have a multi-calyceal collecting system, the initiation of ureteral peristalsis takes place in the renal calyces. In the pig and human ureter, recent evidence suggests that nitric oxide (NO) is an inhibitory mediator that may be involved in the regulation of peristalsis. This study was designed to assess whether the NO synthase/NO/cyclic GMP pathway modulates the motility of pig isolated calyceal smooth muscle. Immunohistochemistry revealed a moderate overall innervation of the smooth muscle layer, and no neuronal or inducible NO synthase (NOS) immunoreactivities. Endothelial NOS immunoreactivities were observed in the urothelium and vascular endothelium, and numerous cyclic GMP-immunoreactive (-IR) calyceal smooth muscle cells were found. As measured by monitoring the conversion of L-arginine to L-citrulline, Ca(2+)-dependent NOS activity was moderate. Assessment of functional effects was performed in tissue baths and showed that NO and SIN-1 decreased spontaneous and induced contractions of isolated preparations in a concentration-dependent manner. In strips exposed to NO, there was a 10-fold increase of the cyclic GMP levels compared with control preparations (P < 0.01). It is concluded that a non-neuronal NOS/NO/cyclic GMP pathway is present in pig calyces, where it may influence motility. The demonstration of cyclic GMP-IR smooth muscle cells suggests that NO acts directly on these cells. This NOS/NO/cyclic GMP pathway may be a target for drugs inhibiting peristalsis of mammalian upper urinary tract. Neurourol. Urodynam. 18:673-685, 1999.     

Different inhibitory effects of volatile anesthetics on T- and L-type voltage-dependent Ca2+ channels in porcine tracheal and bronchial smooth muscles

BACKGROUND: The distal airway is more important in the regulation of airflow resistance than is the proximal airway, and volatile anesthetics have a greater inhibitory effect on distal airway muscle tone. The authors investigated the different reactivities of airway smooth muscles to volatile anesthetics by measuring porcine tracheal or bronchial (third to fifth generation) smooth muscle tension and intracellular concentration of free Ca2+ ([Ca2+]i) and by measuring inward Ca2+ currents (ICa) through voltage-dependent Ca2+ channels (VDCs). METHODS: Intracellular concentration of free Ca2+ was monitored by the 500-nm light emission ratio of Ca2+ indicator fura-2. Isometric tension was measured simultaneously. Whole-cell patch clamp recording techniques were used to investigate the effects of volatile anesthetics on ICa in dispersed smooth muscle cells. Isoflurane (0-1.5 minimum alveolar concentration) or sevoflurane (0-1.5 minimum alveolar concentration) was introduced into a bath solution. RESULTS: The volatile anesthetics tested had greater inhibitory effects on carbachol-induced bronchial smooth muscle contraction than on tracheal smooth muscle contraction. These inhibitory effects by the anesthetics on muscle tension were parallel to the inhibitory effects on [Ca2+]i. Although tracheal smooth muscle cells had only L-type VDCs, some bronchial smooth muscle cells (approximately 30%) included T-type VDC. Each of the two anesthetics significantly inhibited the activities of both types of VDCs in a dose-dependent manner; however, the anesthetics had greater inhibitory effects on T-type VDC activity in bronchial smooth muscle. CONCLUSIONS: The existence of the T-type VDC in bronchial smooth muscle and the high sensitivity of this channel to volatile anesthetics seem to be, at least in part, responsible for the different reactivities to the anesthetics in tracheal and bronchial smooth muscles.     

Inflammation of bronchial smooth muscle in allergic asthma

BACKGROUND: Recent observations in asthma suggest that bronchial smooth muscle is infiltrated by inflammatory cells including mast cells. Such an infiltration may contribute to airway remodelling that is partly due to an increase in smooth muscle mass. Whether muscle increase is the result of smooth muscle cell hypertrophy remains controversial and has not been studied by ultrastructural analysis. A morphometric analysis of airway smooth muscle (ASM) was undertaken in asthmatic patients using electron microscopy to examine the interactions between ASM cells and inflammatory cells. METHODS: ASM specimens were obtained from 14 asthmatic subjects and nine non-asthmatic controls undergoing fibreoptic endoscopy. Inflammatory cell counts were assessed by immunohistochemistry, and ultrastructural parameters were measured using electron microscopy in a blinded fashion on smooth muscle cells and inflammatory cells. RESULTS: ASM from asthmatic patients was infiltrated by an increased number of mast cells and lymphocytes. Smooth muscle cells and their basal lamina were thicker in asthmatic patients (9.5 (0.8) and 1.4 (0.2) microm) than in controls (6.7 (0.4) and 0.7 (0.1) microm). In asthmatics the extracellular matrix was frequently organised in large amounts between ASM cells. Myofibroblasts within smooth muscle bundles were only observed in asthmatics, some of them displaying a close contact with ASM cells. CONCLUSION: In asthma, airway myositis is characterised by a direct interaction between ASM cells and mast cells and lymphocytes. Smooth muscle remodelling was present, including cell hypertrophy and abnormal extracellular matrix deposition moulding ASM cells.     

Effects of volatile anesthetics on response to norepinephrine and acetylcholine in guinea pig atria

The in vitro chronotropic and inotropic effects of norepinephrine and acetylcholine in isolated right and left guinea pig atria were examined in the absence and presence of halothane, isoflurane, and enflurane (0.6 and 1.2 MAC). All three anesthetics elicited dose-dependent reductions in contractile force and spontaneous pacemaker activity. The maximal developed tension observed in the presence of norepinephrine was not altered by the anesthetics and corresponding ED50 values increased only in the presence of 1.2 MAC halothane and 1.2 MAC isoflurane. The anesthetics did not affect (a) the maximal positive chronotropic effect of norepinephrine, (b) the ED50 values for its positive chronotropic effect, and (c) acetylcholine-induced negative inotropic and chronotropic actions and did not induce arrhythmic activity even in the presence of the maximally effective neurotransmitter concentrations. These findings indicate that in isolated guinea pig atria volatile anesthetics, in concentrations up to 1.2 MAC, do not alter the inotropic and chronotropic effects of norepinephrine or acetylcholine and do not induce arrhythmogenic action in the presence of the neurotransmitters. These data suggest that altered atrial responsiveness to adrenergic or muscarinic stimulation does not contribute to the development of anesthetic-induced cardiac arrhythmias.     

Store-operated Ca2+ influx in airway smooth muscle: Interactions between volatile anesthetic and cyclic nucleotide effects

BACKGROUND: Volatile anesthetics produce bronchodilation in part by depleting sarcoplasmic reticulum Ca stores in airway smooth muscle (ASM). Other bronchodilatory drugs are known to act via cyclic nucleotides (cyclic adenosine 3',5'-cyclic monophosphate, cyclic guanosine 3',5'-cyclic monophosphate). Intracellular Ca regulation in ASM involves plasma membrane Ca influx, including that triggered by sarcoplasmic reticulum Ca depletion (store-operated Ca entry [SOCE]). The authors hypothesized that anesthetics and bronchodilatory agents interact in inhibiting SOCE, thus enhancing ASM relaxation. METHODS: In enzymatically dissociated porcine ASM cells imaged using fluorescence microscopy, sarcoplasmic reticulum Ca was depleted by 1 microm cyclopiazonic acid in 0 extracellular Ca, nifedipine, and potassium chloride (preventing Ca influx through L-type channels and SOCE). Extracellular Ca was rapidly reintroduced to selectively activate SOCE in the presence or absence of 1 minimum alveolar concentration (MAC) halothane, isoflurane, or sevoflurane. Anesthetic interference with SOCE regulation by cyclic nucleotides was examined by activating SOCE in the presence of (1) 1 microm acetylcholine, (2) 100 microm dibutryl cyclic adenosine 3',5'-cyclic monophosphate, or (3) 100 microm 8-bromo-cyclic guanosine 3',5'-cyclic monophosphate. RESULTS: SOCE was enhanced by acetylcholine, whereas volatile anesthetics and both cyclic nucleotides partially inhibited Ca influx. Preexposure to 1 or 2 MAC anesthetic (halothane > isoflurane > sevoflurane) inhibited SOCE. Only halothane and isoflurane inhibited acetylcholine-induced augmentation of Ca influx, and significantly potentiated cyclic nucleotide inhibition such that no influx was observed in the presence of anesthetics and cyclic nucleotides. CONCLUSIONS: These data indicate that volatile anesthetics prevent sarcoplasmic reticulum refilling by inhibiting SOCE and enhancing cyclic nucleotide blunting of Ca influx in ASM. Such interactions likely result in substantial airway relaxation in the presence of both anesthetics and bronchodilatory agents such as beta agonists or nitric oxide.