This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a colleague Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (3) Citing Articles via Google Scholar Google Scholar Articles by Chen, X. Articles by Namiki, A. Search for Related Content PubMed PubMed Citation Articles by Chen, X. Articles by Namiki, A.

---

GENERAL ARTICLES

Interaction Between Volatile Anesthetics and Hypoxia in Porcine Tracheal Smooth Muscle

Department of Anesthesiology, Sapporo Medical University School of Medicine, Sapporo, Japan

Address correspondence and reprint requests to Michiaki Yamakage, MD, PhD, Department of Anesthesiology, Sapporo Medical University School of Medicine, South 1, West 16, Chuo-ku, Sapporo, Hokkaido 060-8543, Japan. Address e-mail to yamakage{at}sapmed .ac.jp.

	Abstract

Top Abstract Introduction Methods Results Discussion References

 
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 Ca²⁺ ([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 µM carbachol with a concomitant contraction. Volatile anesthetics significantly inhibited both carbachol-induced muscle contraction and increase in [Ca²⁺]_i. Hypoxia bubbled with 95% N₂/5% 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.

	Introduction

Top Abstract Introduction Methods Results Discussion References

 
Isoflurane and sevoflurane are potent bronchodilators (1,2) useful for treatment of patients with asthma in the operating room (3) and intensive care unit (4,5). The direct inhibitory mechanisms of these anesthetics on airway smooth muscle contraction are caused by decreases in both the intracellular concentration of free Ca²⁺ ([Ca²⁺]_i) and the activity of protein kinase C (PKC) (2,6). Intracellular Ca²⁺ plays a central role in regulation of the smooth muscle tone (7), and PKC sensitizes contractile elements to Ca²⁺ or activates a Ca²⁺-independent mechanism (6,8).

Hypoxia can occur during acute asthma attacks (9,10). Hypoxia also inhibits airway smooth muscle contraction (11–13); however, the mechanism is still unknown. Fernandes et al. (14) suggested, from measurements of muscle tension, that hypoxia attenuated the airway tone by altering the entry of extracellular Ca²⁺ into the airway smooth muscle. Aakjaer and Lombard (15) and Mochizuki and Jiang (16) found by measuring [Ca²⁺]_i that hypoxia did not change [Ca²⁺]_i in arterial smooth muscle cells but rather, increased [Ca²⁺]_i in myocardial cells. However, there have been no other detailed studies either on the hypoxic effect on [Ca²⁺]_i or on the interaction between hypoxia and volatile anesthetics in airway smooth muscle.

We investigated the direct interaction between volatile anesthetics, isoflurane and sevoflurane, and hypoxia in porcine tracheal smooth muscles in vitro by simultaneously measuring muscle tension and [Ca²⁺]_i.

	Methods

Top Abstract Introduction Methods Results Discussion References

 
The protocol for this study was approved by our committee on animal research. Tissue preparation was performed according to the previously described method (6). The tracheae were excised quickly from pigs (weighing 30–45 kg), and the epithelium, cartilage, and connective tissue were stripped from the smooth muscle. Tracheal smooth muscle strips (approximately 1 mm wide and 8 mm long) were pretreated with 5 µM acetoxymethyl ester of fura-2 (fura-2/AM), an indicator of Ca²⁺, in a physiological salt solution (PSS) containing 0.025% (vol/vol) cremophor EL for 6–7 h at room temperature (22°C–24°C). The PSS contained (in mM): 136.9 NaCl, 5.4 KCl, 1.5 CaCl₂, 1.0 MgCl₂, 23.9 NaHCO₃, 5.5 glucose, and 0.01 EDTA. This solution was saturated with a gas mixture of 95% O₂/5% CO₂, at 37°C (pH approximately 7.4). The fura-2-loaded muscle strip was held in a temperature-controlled (37°C) organ bath, and one end of the muscle strip was connected to a strain-gauge transducer (LVS-20GA; Kyowa, Tokyo, Japan). Experiments were performed with a fluorescence spectrometer (CAF-100; Japan Spectroscopic, Tokyo, Japan). Excitation light was passed through a rotating filter wheel (48 Hz) that contained 340- and 380-nm filters. The light emitted from the muscle strip at 500 nm was measured with a photomultiplier. The ratio of the fluorescence caused by excitation at 340 nm to that at 380 nm (R_340/380) was calculated and used as an indicator of [Ca²⁺]_i (6,8). PSS bubbled with 95% O₂/5% CO₂ was used for the control bath solution.

Contractions were induced by 1 µM carbachol, a potent muscarinic receptor agonist. After the contractions reached a steady state, the tissues were exposed to a bath solution equilibrated with one of two volatile anesthetics: isoflurane, 0.6 (1.0% at the vaporizer), 1.2 (2.0%), or 1.8 (3.0%) minimum alveolar concentrations (MAC) in pigs (17); or sevoflurane, 0.4 (1.0%), 0.8 (2.0%), or 1.2 (3.0%) MAC in pigs (18). Similar to this experiment, the tissue strips were exposed to mild or severe hypoxia (30% N₂/65% O₂/5% CO₂, or 95% N₂/5% CO₂, respectively) with or without the volatile anesthetics during carbachol-induced contraction. To investigate the role of Ca²⁺ store during the hypoxia with or without volatile anesthetics, the same protocols previously described were performed by using a Ca²⁺-free bath solution with 100 µM EGTA (19).

Because there was a possibility that hypoxia per se could change the intracellular pH (pH_i), resulting in changes of both airway smooth muscle contractility (20) and the fura-2 affinity for Ca²⁺ (21), we confirmed the effect of hypoxia on pH_i of the tracheal smooth muscle strips by the use of a fluorescence technique (20). Muscle strips were treated with 5 µM acetoxymethyl ester of 2',7'-bis(2-carboxyethyl)-5,6-carboxyfluorescein (BCECF/AM), an indicator of pH, in PSS containing 0.025% (vol/vol) cremophor EL for 60 min at room temperature. The pH_i experiments were performed with a spectrometer as previously described by using excitation wavelengths of 450 and 500 nm and a 540 nm photomultiplier filter. The ratio of the fluorescence caused by excitation at 500 nm to that at 450 nm was calculated from successive illumination periods and referred to as R_500/450. At the end of each experiment, R_500/450 was calibrated by using the high-K⁺-nigericin technique (22).

The vaporizers for isoflurane and sevoflurane were calibrated with an infrared anesthetic gas monitor (5250 RGM; Datex-Ohmeda, Madison, WI). Concentrations of the anesthetics in bath solution samples were analyzed with a gas chromatograph (GC-17A; Shimadzu, Kyoto, Japan). The mean concentrations of isoflurane in the solution (1.0%, 2.0%, and 3.0% in the gas phase) were 0.27, 0.58, and 0.84 mM, respectively, whereas the mean concentrations of sevoflurane in the solution (1.0%, 2.0%, and 3.0% in the gas phase) were 0.17, 0.33, and 0.56 mM, respectively. Each concentration of the anesthetic had a close linear correlation with each concentration of the anesthetic in the gas phase. The percentage of O₂ in the gas phase was monitored continuously during the experiments by using a calibrated O₂ tension sensor and monitor (OS-1000 and OM-400; Aika, Tokyo, Japan). We also measured the O₂ tension in the bath solution by using a blood gas analysis apparatus (Rapidpoint 400; Bayer Medical, Tokyo, Japan). Concentrations of O₂ reached a steady state in the organ bath within 60–90 s. O₂ at 95%, 30%, and 0%, bubbled into the organ bath produced O₂ tensions of 515, 152, and 22 mm Hg, respectively (n = 5 each). Tissues were typically exposed to each O₂ tension for 20–30 min.

The following drugs and chemicals were used: fura-2/AM, BCECF/AM (Dojindo, Kumamoto, Japan), EDTA (Katayama, Osaka, Japan), carbachol, EGTA, cremophor EL, nigericin (Sigma Chemical, St. Louis, MO), sevoflurane (Maruishi, Osaka, Japan), and isoflurane (Ohio Medical, Madison, WI).

A total of 56 pigs were used in this study, and the data are expressed as mean ± SD. For the measurement of [Ca²⁺]_i and muscle tension, carbachol-induced sustained changes in [Ca²⁺]_i and muscle tension were used as references (100%). Data were analyzed by using one-way or two-way analysis of variance for repeated measurements, and Fisher’s test was used as a post hoc test. In all comparisons, P < 0.05 was considered significant.

	Results

Top Abstract Introduction Methods Results Discussion References

 
Under the condition of bubbling with 95% O₂/5% CO₂, the ratio R_340/380, an indicator of [Ca²⁺]_i, was rapidly increased by carbachol (1 µM), with a concomitant contraction (Fig. 1A). [Ca²⁺]_i and muscle tension reached their respective peaks in 20–60 s. Exposure to 1.8 MAC isoflurane significantly decreased both carbachol-induced muscle contraction and increase in [Ca²⁺]_i. Severe hypoxia bubbled with 95% N₂/5% CO₂ also inhibited the muscle contraction by 30%; however, it conversely increased the [Ca²⁺]_i by 20% (Fig. 1B). The effects of 1.8 MAC isoflurane with severe hypoxia are shown in Figure 1C. Isoflurane with hypoxia substantially inhibited carbachol-induced muscle contraction with a decrease in [Ca²⁺]_i. Linear relationships were observed between anesthetic potencies and percentage of response of muscle tension and between anesthetic potencies and percentage of response of [Ca²⁺]_i (Fig. 2). Exposure to hypoxia significantly enhanced the inhibitory effects of these volatile anesthetics on carbachol-induced muscle contraction, whereas the decreases in [Ca²⁺]_i by the anesthetics were significantly prevented by the hypoxia. We also tested the effect of hypoxia or volatile anesthetics on the resting muscle tension and [Ca²⁺]_i. There were no statistical changes in muscle tension or [Ca²⁺]_i by hypoxia or volatile anesthetics tested (n = 3 each, data not shown).

View larger version (14K): [in this window] [in a new window]   Figure 1. Representative data of the effect of interaction between 1.8 minimum alveolar concentration (MAC) isoflurane and severe hypoxia (bubbled with 95% N2/5% CO2) on muscle tension and [Ca2+]i (indicated by R340/380) of carbachol-stimulated smooth muscle in the presence of 1.5 mM external Ca2+.

View larger version (27K): [in this window] [in a new window]   Figure 2. The relationships between anesthetic potencies, indicated by minimum alveolar concentration (MAC), and percentage of response of muscle tension and between anesthetic potencies and percentage of response of [Ca2+]i (indicated by R340/380) in the presence of 1.5 mM external Ca2+. Mild and severe hypoxia exposure to hypoxia bubbled with 30% O2/65% N2/5% CO2 and with 95% N2/5% CO2, respectively. Exposure to hypoxia significantly enhanced the inhibitory effects of the volatile anesthetics on carbachol-induced muscle contraction, whereas the decreases in [Ca2+]i by the volatile anesthetics were significantly prevented by hypoxia. Data are expressed as mean ± SD (n = 7, *P < 0.05 versus 0 MAC anesthetic, P < 0.05, P < 0.01 versus 95% O2/5% CO2).

View larger version (13K): [in this window] [in a new window]   Figure 3. Representative data of the effect of interaction between 1.2 minimum alveolar concentration (MAC) sevoflurane and severe hypoxia (bubbled with 95% N2/5% CO2) on muscle tension and [Ca2+]i (indicated by R340/380) of carbachol-stimulated smooth muscle in the absence of external Ca2+ (with 100 µM EGTA).

View larger version (26K): [in this window] [in a new window]   Figure 4. The relationships between anesthetic potencies, represented by minimum alveolar concentration (MAC), and percentage of response of muscle tension and between anesthetic potencies and percentage of response of [Ca2+]i (indicated by R340/380) in the absence of external Ca2+ (with 100 µM EGTA). Mild and severe hypoxia exposure to hypoxia bubbled with 30% O2/65% N2/5% CO2 and with 95% N2/5% CO2, respectively. Both volatile anesthetics and hypoxia significantly inhibited muscle contraction in a gradient-dependent manner. In contrast, the volatile anesthetics tested had no effects on [Ca2+]i, whereas hypoxia significantly increased [Ca2+]i in a gradient-dependent manner. Data are expressed as mean ± SD (n = 7, *P < 0.05 versus 0 MAC anesthetic, P < 0.05, P < 0.01 versus 95% O2/5% CO2).

	Discussion

Top Abstract Introduction Methods Results Discussion References

 
The principal findings of our study are that, in porcine tracheal smooth muscle in vitro, exposure to hypoxia significantly inhibited carbachol-induced airway smooth muscle contraction with an increase in [Ca²⁺]_i with or without external Ca²⁺, and that the volatile anesthetics, isoflurane and sevoflurane, with hypoxia had far more inhibitory effects on the smooth muscle contraction than did those with oxygen (Figs. 2 and 4). Because [Ca²⁺]_i plays a central role in the regulation of airway smooth muscle tone (7), a possible mechanism for the relaxation by hypoxia appeared to be a decrease in [Ca²⁺]_i. We, however, provided direct evidence by using a fluorescence technique that hypoxia inhibited airway smooth muscle contraction accompanied by an increase in [Ca²⁺]_i. The following two cellular mechanisms contribute to increases in [Ca²⁺]_i: 1) Ca²⁺ release from intracellular Ca²⁺ stores, especially sarcoplasmic reticulum, and 2) Ca²⁺ influx through cell membrane-associated voltage-dependent Ca²⁺ channels (VDCCs) and voltage-independent receptor-operated Ca²⁺ channels (7,23,24). Because sustained contraction of airway smooth muscle requires the continued entry of extracellular Ca²⁺ (25), and blockade of VDCCs suppresses the sustained increase in [Ca²⁺]_i in agonist-stimulated airway smooth muscle (8), Ca²⁺ influx through VDCCs is most important in the regulation of [Ca²⁺]_i homeostasis. The direct effects of hypoxia on [Ca²⁺]_i in this study did not change even when the muscle strips were exposed to a Ca²⁺-free bath solution, demonstrating that the increase in [Ca²⁺]_i by hypoxia is independent of extracellular Ca²⁺. It is, therefore, likely that the increase in [Ca²⁺]_i by hypoxia is caused by the Ca²⁺ release from sarcoplasmic reticulum. The volatile anesthetics tested had no effect on [Ca²⁺]_i induced by hypoxia in the Ca²⁺-free bath solution (Figs. 3 and 4). This result may support our hypothesis because isoflurane and sevoflurane in large doses had little inhibitory effect on Ca²⁺ release from intracellular stores (2,19). During hypoxic exposure, pH_i might be another important regulator for Ca²⁺ homeostasis because hypoxia may be associated with acid production caused by anoxic metabolism (16). Lattanzio (21) also reported that a decrease in pH_i <7.0 could change the Ca²⁺ affinity for fura-2, indicating that R_340/380 would not express the [Ca²⁺]_i correctly. However, pH_i measured by a pH indicator, BCECF, did not change during exposure to hypoxia in this study. Although hypoxia may enhance acid production, intracellular buffer system and acid extrusion could maintain the pH_i near the control level (16), and it is unlikely that changes in pH_i in airway smooth muscle play any role in changes in [Ca²⁺]_i during exposure to hypoxia.

Based on these findings, it appears that Ca²⁺-independent mechanisms are important in hypoxia-induced airway smooth muscle relaxation. At first, the depletion of the energy stores (e.g., ATP) needed for the myosin phosphorylation should be considered as a regulator in the relaxation. It has, however, been demonstrated that the intracellular concentration of ATP was sufficient for maintaining airway smooth muscle contraction during hypoxia (26). Moreover, we found in this study that pH_i did not change during hypoxia, which is also inconsistent with the hypothesis of energy exhaustion. Cyclic AMP, which inhibits airway smooth muscle contraction independent of Ca²⁺, could be another regulator of relaxation during hypoxia. However, it is also unlikely that an increase in the intracellular concentration of cyclic AMP is involved in the hypoxic-inhibition of airway smooth muscle contraction because Fernandes et al. (14) demonstrated that indomethacin (a cyclooxygenase inhibitor) and propranolol (a ß-adrenoceptor antagonist) each failed to inhibit the hypoxic response on airway smooth muscle. Finally, the inhibition of PKC activity should be considered as an important regulator of hypoxia-induced airway smooth muscle relaxation. Under basal conditions, PKC is thought to be located mainly in cytosol and to be "deactivated." After carbachol stimulation, PKC is rapidly translocated to the membrane to be "activated" (6,26). PKC acts to sensitize contractile elements to Ca²⁺ or activates a Ca²⁺-independent mechanism by inhibiting myosin light chain phosphatase. Therefore, the inhibitory effects of hypoxia on porcine airway smooth muscle contraction may partly involve the suppression of this PKC activity. Investigations of this possibility, such as measurement of PKC translocation, must be the subject of future research.

Another result from our study showed that hypoxia potentiated the inhibitory effects of volatile anesthetics on airway smooth muscle (Fig. 2). This result parallels those of other basic experiments and clinical observations that volatile anesthetics are useful in the treatment of severe asthmatic attack (1,3–5). The addition of volatile anesthetics with oxygen significantly decreased [Ca²⁺]_i as well as muscle tension, which is similar to previous observations (2). These volatile anesthetics with hypoxia, however, substantially decreased muscle tension more than did those with oxygen, and the [Ca²⁺]_i did not decrease additionally. This result indicates that hypoxia potentiated the inhibitory effects of these anesthetics on airway smooth muscle by Ca²⁺-independent mechanisms. This is strongly supported by the effects of the interaction between volatile anesthetics and hypoxia on airway smooth muscle contraction with a Ca²⁺-free solution (Figs. 3 and 4).

In conclusion, hypoxia inhibits agonist-induced porcine tracheal smooth muscle contraction with an increase in [Ca²⁺]_i, which comes from intracellular Ca²⁺ stores. The Ca²⁺-independent relaxation effects of hypoxia might be mediated by PKC. In addition, 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 too much oxygen partially attenuates the inhibitory effect of volatile anesthetics on airway smooth muscle contractility.

	Acknowledgments

 
Supported, in part, by grant-in-aid 10770762 for research from the Ministry of Education, Science and Culture, Tokyo, Japan, and an incentive grant 98-B-02 for research from the Akiyama Research Foundation, Sapporo, Japan.

	References

Top Abstract Introduction Methods Results Discussion References

 

1. Mitsuhata H, Saitoh J, Shimizu R, et al. Sevoflurane and isoflurane protect against bronchospasm in dogs. Anesthesiology 1994; 81: 1230–4.[Web of Science][Medline]
2. Yamakage M, Kohro S, Kawamata T, Namiki A. Inhibitory effects of four inhaled anesthetics on canine tracheal smooth muscle contraction and intracellular Ca²⁺ concentration. Anesth Analg 1993; 77: 67–72.[Abstract/Free Full Text]
3. Rooke GA, Choi J-H, Bishop MJ. The effect of isoflurane, halothane, sevoflurane, and thiopental/nitrous oxide on respiratory system resistance after tracheal intubation. Anesthesiology 1997; 86: 1294–9.[Web of Science][Medline]
4. Maltais F, Sovilj M, Goldberg P, Gottfried SB. Respiratory mechanics in status asthmaticus: effects of inhalational anesthesia. Chest 1994; 106: 1401–6.[Abstract/Free Full Text]
5. Johnston RG, Noseworthy TW, Friesen EG, et al. Isoflurane therapy for status asthmaticus in children and adults. Chest 1990; 97: 698–701.[Abstract/Free Full Text]
6. Yamakage M. Direct inhibitory mechanisms of halothane on canine tracheal smooth muscle contraction. Anesthesiology 1992; 77: 546–53.[Web of Science][Medline]
7. van Breemen C, Saida K. Cellular mechanisms regulating [Ca²⁺]_i smooth muscle. Annu Rev Physiol 1989; 51: 315–29.[Web of Science][Medline]
8. Ozaki H, Kwon S-C, Tajimi M, Karaki H. Changes in cytosolic Ca²⁺ and contraction induced by various stimulants and relaxants in canine tracheal smooth muscle. Pflügers Arch 1990; 416: 351–9.[Web of Science][Medline]
9. Nichols DG. Emergency management of status asthmaticus in children. Pediatr Ann 1996; 25: 394–400.[Web of Science][Medline]
10. Kunitoh H, Watanabe K, Sajima Y. Clinical features to predict hypoxia and/or hypercapnia in acute asthma attacks. J Asthma 1994; 31: 401–7.[Web of Science][Medline]
11. Stephens NL, Kroeger E. Effect of hypoxia on airway smooth muscle mechanics and electrophysiology. J Appl Physiol 1970; 28: 630–5.[Free Full Text]
12. Stephens NL. Study of reversibility of effects of hypoxia in airway smooth muscle. Can J Physiol Pharmacol 1977; 55: 828–32.[Web of Science][Medline]
13. Paterson NA, Hamilton JT, Yaghi A, Miller DS. Effect of hypoxia on responses of respiratory smooth muscle to histamine and LTD4. J Appl Physiol 1988; 64: 435–40.[Abstract/Free Full Text]
14. Fernandes LB, Stuart-Smith K, Croxton TL, Hirshman CA. Role of Ca²⁺ entry in the modulation of airway tone by hypoxia. Am J Physiol 1993; 264: L284–9.[Abstract/Free Full Text]
15. Aalkjaer C, Lombard JH. Effect of hypoxia on force, intracellular pH and Ca²⁺ concentration in rat cerebral and mesenteric small arteries. J Physiol 1995; 482: 409–19.[Abstract/Free Full Text]
16. Mochizuki S, Jiang C. Na⁺ /Ca^{+ +} exchanger and myocardial ischemia/reperfusion. Jpn Heart J 1998; 39: 707–14.[Medline]
17. Tranquilli WJ, Thurmon JC, Benson GJ. Anesthetic potency of nitrous oxide in young swine (Sus scrofa). Am J Vet Res 1985; 46: 58–60.[Web of Science][Medline]
18. Manohar M, Parks CM. Porcine systemic and regional organ blood flow during 1.0 and 1.5 minimum alveolar concentrations of sevoflurane anesthesia without and with 50% nitrous oxide. J Pharmacol Exp Ther 1984; 231: 640–8.[Abstract/Free Full Text]
19. Yamakage M, Kohro S, Matsuzaki T, et al. Role of intracellular Ca²⁺ stores in the inhibitory effect of halothane on airway smooth muscle contraction. Anesthesiology 1998; 89: 165–73.[Web of Science][Medline]
20. Yamakage M, Kohro S, Yamauchi M, Namiki A. The effects of extracellular pH on intracellular pH, Ca²⁺ and tension of canine tracheal smooth muscle strips. Life Sci 1995; 56: PL175–80.
21. Lattanzio FA Jr. The effects of pH and temperature on fluorescent calcium indicators as determined with chelex-100 and EDTA buffer systems. Biochem Biophys Res Commun 1990; 171: 102–8.[Web of Science][Medline]
22. Thomas JA, Buchsbaum RN, Zimniak A, Racker E. Intracellular pH measurements in Ehrlich ascites tumor cells utilizing spectroscopic probes generated in situ. Biochemistry 1979; 18: 2210–8.[Medline]
23. Kajita J, Yamaguchi H. Calcium mobilization by muscarinic cholinergic stimulation in bovine single airway smooth muscle. Am J Physiol 1993; 264: L496–503.[Abstract/Free Full Text]
24. Coburn RF, Baron CB. Coupling mechanisms in airway smooth muscle. Am J Physiol 1990; 258: L119–33.[Abstract/Free Full Text]
25. Bourreau JP, Abela AP, Kwan Y, Daniel EE. Acetylcholine Ca²⁺ stores refilling directly involves a dihydropyridine-sensitive channel in dog trachea. Am J Physiol 1991; 261: C497–505.[Abstract/Free Full Text]
26. Nishizuka Y. Studies and perspectives of protein kinase C. Science 1986; 233: 305–12.[Abstract/Free Full Text]

This article has been cited by other articles:

				J.-H. Baumert, K. E. Hecker, M. Hein, M. Reyle-Hahn, N. A. Horn, and R. Rossaint Effects of xenon anaesthesia on the circulatory response to hypoventilation Br. J. Anaesth., August 1, 2005; 95(2): 166 - 171. [Abstract] [Full Text] [PDF]

				N. Ouedraogo, R. Marthan, and a. E. Roux The Effects of Propofol and Etomidate on Airway Contractility in Chronically Hypoxic Rats Anesth. Analg., April 1, 2003; 96(4): 1035 - 1041. [Abstract] [Full Text] [PDF]

This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a colleague Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (3) Citing Articles via Google Scholar Google Scholar Articles by Chen, X. Articles by Namiki, A. Search for Related Content PubMed PubMed Citation Articles by Chen, X. Articles by Namiki, A.