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Obara K, Shigematsu M, Takahasi H, Iiboshi Y, Yoshioka K, Kasuya Y, Tanaka Y. Pharmacological properties of β-adrenoceptors mediating rat superior mesenteric artery relaxation and the effects of chemical sympathetic denervation. Life Sci 2020; 241:117155. [PMID: 31837330 DOI: 10.1016/j.lfs.2019.117155] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2019] [Revised: 12/06/2019] [Accepted: 12/08/2019] [Indexed: 10/25/2022]
Abstract
AIMS β-Adrenoceptors (β-ADRs) mediating the relaxation of rat superior mesenteric arteries (SMAs) were pharmacologically identified, and the effects of chemical sympathetic denervation on β-ADR-mediated relaxation were examined. MAIN METHODS The tension changes of endothelium-denuded SMAs were isometrically recorded and the mRNA of endothelium-denuded SMA β-ADR was detected using RT-PCR. KEY FINDINGS In endothelium-denuded SMAs contracted with ≥10-7 M phenylephrine (an α1-ADR agonist), isoprenaline (a β-ADR agonist)-induced relaxation was competitively inhibited by 3 × 10-9-10-8 M propranolol (a β1,2-ADR antagonist), but not further affected by ≥10-8 M propranolol. Although isoprenaline-induced relaxation was not affected by ICI-118,551 (10-9-10-8 M; a β2-ADR antagonist), it was competitively inhibited by atenolol (10-7-3 × 10-7 M; a β1-ADR antagonist) in the presence of ICI-118,551. In the presence of 10-7 M propranolol, isoprenaline- and CGP-12177A (a β3-ADR partial agonist)-induced relaxation was competitively inhibited by high concentrations of bupranolol (a β1,2,3-ADR antagonist), with pA2 values of 6.49 and 5.76, respectively. We detected the mRNA of β1- and β3-ADRs in endothelium-denuded SMAs. Treatment with 6-hydroxydopamine (a catecholaminergic neurotoxin) reduced maximal isoprenaline-induced relaxation in the presence and absence of 10-7 M propranolol, but not CGP-12177A-induced relaxation. SIGNIFICANCE Isoprenaline-induced relaxation of rat SMAs is mediated by β1- and β3-ADRs. β-ADR-mediated relaxation of rat SMAs is shown to be attenuated by chemical sympathetic denervation. The differences in the effects of bupranolol and chemical sympathetic denervation on the responses to isoprenaline and CGP-12177A in rat SMAs might be explained by the possible presence of multiple β3-ADRs with different pharmacological properties.
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Affiliation(s)
- Keisuke Obara
- Department of Chemical Pharmacology, Faculty of Pharmaceutical Sciences, Toho University, Miyama 2-2-1, Funabashi-City, Chiba 274-8510, Japan
| | - Mai Shigematsu
- Department of Chemical Pharmacology, Faculty of Pharmaceutical Sciences, Toho University, Miyama 2-2-1, Funabashi-City, Chiba 274-8510, Japan
| | - Hiromi Takahasi
- Department of Chemical Pharmacology, Faculty of Pharmaceutical Sciences, Toho University, Miyama 2-2-1, Funabashi-City, Chiba 274-8510, Japan
| | - Yuri Iiboshi
- Department of Chemical Pharmacology, Faculty of Pharmaceutical Sciences, Toho University, Miyama 2-2-1, Funabashi-City, Chiba 274-8510, Japan
| | - Kento Yoshioka
- Department of Chemical Pharmacology, Faculty of Pharmaceutical Sciences, Toho University, Miyama 2-2-1, Funabashi-City, Chiba 274-8510, Japan
| | - Yoshitoshi Kasuya
- Department of Biochemistry and Molecular Pharmacology, Graduate School of Medicine, Chiba University, 1-8-1 Inohana, Chiba 260-8670, Japan
| | - Yoshio Tanaka
- Department of Chemical Pharmacology, Faculty of Pharmaceutical Sciences, Toho University, Miyama 2-2-1, Funabashi-City, Chiba 274-8510, Japan.
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Obara K, Suzuki S, Shibata H, Yoneyama N, Hamamatsu S, Yamaki F, Higai K, Tanaka Y. Noradrenaline-Induced Relaxation of Urinary Bladder Smooth Muscle Is Primarily Triggered through the β<sub>3</sub>-Adrenoceptor in Rats. Biol Pharm Bull 2019; 42:736-743. [DOI: 10.1248/bpb.b18-00903] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Affiliation(s)
- Keisuke Obara
- Department of Chemical Pharmacology, Faculty of Pharmaceutical Sciences, Toho University
| | - Serena Suzuki
- Department of Chemical Pharmacology, Faculty of Pharmaceutical Sciences, Toho University
| | - Hiroko Shibata
- Department of Chemical Pharmacology, Faculty of Pharmaceutical Sciences, Toho University
| | - Naoki Yoneyama
- Department of Chemical Pharmacology, Faculty of Pharmaceutical Sciences, Toho University
| | - Shoko Hamamatsu
- Department of Chemical Pharmacology, Faculty of Pharmaceutical Sciences, Toho University
| | - Fumiko Yamaki
- Department of Chemical Pharmacology, Faculty of Pharmaceutical Sciences, Toho University
| | - Koji Higai
- Laboratory of Medical Biochemistry, Faculty of Pharmaceutical Sciences, Toho University
| | - Yoshio Tanaka
- Department of Chemical Pharmacology, Faculty of Pharmaceutical Sciences, Toho University
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Chino D, Sone T, Yamazaki K, Tsuruoka Y, Yamagishi R, Shiina S, Obara K, Yamaki F, Higai K, Tanaka Y. Pharmacological identification of β-adrenoceptor subtypes mediating isoprenaline-induced relaxation of guinea pig colonic longitudinal smooth muscle. J Smooth Muscle Res 2018. [PMID: 29540623 PMCID: PMC5863046 DOI: 10.1540/jsmr.54.13] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Object We aimed to identify the β-adrenoceptor (β-AR) subtypes involved in isoprenaline-induced relaxation of guinea pig colonic longitudinal smooth muscle using pharmacological and biochemical approaches. Methods Longitudinal smooth muscle was prepared from the male guinea pig ascending colon and contracted with histamine prior to comparing the relaxant responses to three catecholamines (isoprenaline, adrenaline, and noradrenaline). The inhibitory effects of subtype-selective β-AR antagonists on isoprenaline-induced relaxation were then investigated. Results The relaxant potencies of the catecholamines were ranked as: isoprenaline > noradrenaline ≈ adrenaline, whereas the rank order was isoprenaline > noradrenaline > adrenaline in the presence of propranolol (a non-selective β-AR antagonist; 3 × 10-7 M). Atenolol (a selective β1-AR antagonist; 3 × 10-7-10-6 M) acted as a competitive antagonist of isoprenaline-induced relaxation, and the pA2 value was calculated to be 6.49 (95% confidence interval: 6.34-6.83). The relaxation to isoprenaline was not affected by ICI-118,551 (a selective β2-AR antagonist) at 10-9-10-8 M, but was competitively antagonized by 10-7-3 × 10-7 M, with a pA2 value of 7.41 (95% confidence interval: 7.18-8.02). In the presence of propranolol (3 × 10-7 M), the relaxant effect of isoprenaline was competitively antagonized by bupranolol (a non-selective β-AR antagonist), with a pA2 value of 5.90 (95% confidence interval: 5.73-6.35). Conclusion These findings indicated that the β-AR subtypes involved in isoprenaline-induced relaxation of colonic longitudinal guinea pig muscles are β1-AR and β3-AR.
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Affiliation(s)
- Daisuke Chino
- Department of Chemical Pharmacology, Faculty of Pharmaceutical Sciences, Toho University, 2-2-1 Miyama, Funabashi-City, Chiba 274-8510, Japan.,Department of Pharmacotherapy, Faculty of Pharmaceutical Sciences, Nihon Pharmaceutical University, 10281 Komuro, Ina-machi, Kita-Adachi-gun, Saitama 362-0806, Japan
| | - Tomoyo Sone
- Department of Chemical Pharmacology, Faculty of Pharmaceutical Sciences, Toho University, 2-2-1 Miyama, Funabashi-City, Chiba 274-8510, Japan
| | - Kumi Yamazaki
- Department of Chemical Pharmacology, Faculty of Pharmaceutical Sciences, Toho University, 2-2-1 Miyama, Funabashi-City, Chiba 274-8510, Japan
| | - Yuri Tsuruoka
- Department of Chemical Pharmacology, Faculty of Pharmaceutical Sciences, Toho University, 2-2-1 Miyama, Funabashi-City, Chiba 274-8510, Japan
| | - Risa Yamagishi
- Department of Chemical Pharmacology, Faculty of Pharmaceutical Sciences, Toho University, 2-2-1 Miyama, Funabashi-City, Chiba 274-8510, Japan
| | - Shunsuke Shiina
- Department of Chemical Pharmacology, Faculty of Pharmaceutical Sciences, Toho University, 2-2-1 Miyama, Funabashi-City, Chiba 274-8510, Japan
| | - Keisuke Obara
- Department of Chemical Pharmacology, Faculty of Pharmaceutical Sciences, Toho University, 2-2-1 Miyama, Funabashi-City, Chiba 274-8510, Japan
| | - Fumiko Yamaki
- Department of Chemical Pharmacology, Faculty of Pharmaceutical Sciences, Toho University, 2-2-1 Miyama, Funabashi-City, Chiba 274-8510, Japan
| | - Koji Higai
- Laboratory of Medical Biochemistry, Faculty of Pharmaceutical Sciences, Toho University, 2-2-1 Miyama, Funabashi-City, Chiba 274-8510, Japan
| | - Yoshio Tanaka
- Department of Chemical Pharmacology, Faculty of Pharmaceutical Sciences, Toho University, 2-2-1 Miyama, Funabashi-City, Chiba 274-8510, Japan
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Afeli SAY, Hristov KL, Petkov GV. Do β3-adrenergic receptors play a role in guinea pig detrusor smooth muscle excitability and contractility? Am J Physiol Renal Physiol 2012; 302:F251-63. [PMID: 21993887 PMCID: PMC3340921 DOI: 10.1152/ajprenal.00378.2011] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2011] [Accepted: 10/11/2011] [Indexed: 11/22/2022] Open
Abstract
In many species, β3-adrenergic receptors (β3-ARs) have been reported to play a primary role in pharmacologically induced detrusor smooth muscle (DSM) relaxation. However, their role in guinea pig DSM remains controversial. The aim of this study was to investigate whether β3-ARs are expressed in guinea pig DSM and to evaluate how BRL37344 and L-755,507, two selective β3-AR agonists, modulate guinea pig DSM excitability and contractility. We used a combined experimental approach including RT-PCR, patch-clamp electrophysiology, and isometric DSM tension recordings. β3-AR mRNA message was detected in freshly isolated guinea pig DSM single cells. BRL37344 but not L-755,507 caused a slight decrease in DSM spontaneous phasic contraction amplitude and frequency in a concentration-dependent manner. In the presence of atropine (1 μM), only the spontaneous phasic contractions frequency was inhibited by BRL37344 at higher concentrations. Both BRL37344 and L-755,507 significantly decreased DSM carbachol-induced phasic and tonic contractions in a concentration-dependent manner. However, only BRL37344 inhibitory effect was partially antagonized by SR59230A (10 μM), a β3-AR antagonist. In the presence of atropine, BRL37344 and L-755,507 had no inhibitory effect on electrical field stimulation-induced contractions. Patch-clamp experiments showed that BRL37344 (100 μM) did not affect the DSM cell resting membrane potential and K(+) conductance. Although β3-ARs are expressed at the mRNA level, they play a minor to no role in guinea pig DSM spontaneous contractility without affecting cell excitability. However, BRL37344 and L-755,507 have pronounced inhibitory effects on guinea pig DSM carbachol-induced contractions. The study outlines important DSM β3-ARs species differences.
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Affiliation(s)
- Serge A Y Afeli
- Dept. of Pharmaceutical and Biomedical Sciences, South Carolina College of Pharmacy, Univ. of South Carolina, Columbia, SC 29208, USA
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Tanaka Y, Takahashi H, Shibata S, Namiki K, Kimura S, Koike K, Kasuya Y. Functional analysis of guinea pig β1-adrenoceptor. J Recept Signal Transduct Res 2011; 31:395-401. [PMID: 21961942 DOI: 10.3109/10799893.2011.610109] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Although similarity of pharmacological responses to certain stimuli between guinea pigs and humans has been reported, this has been poorly defined by a molecular biological approach. In this study, we cloned the gene of guinea pig ?1-adrenoceptor (ADRB1). The deduced amino acid sequence of guinea pig ADRB1 (467-aa) showed 91% and 92% identity with the human and rat ADRB1 sequences, respectively. Using HEK293T cells expressing guinea pig, human and rat ADRB1s independently, we elucidated the functional characteristics of each ADRB1. The ligand-binding profiles and the concentration-response relationships for isoprenaline-induced cyclic adenosine monophosphate (cAMP) production were similar among the three ADRB1s. Isoprenaline also induced phosphorylation of extracellular-signal related kinases (ERK) through ADRB1s in a concentration-dependent manner. The minimum effective concentration of isoprenaline for phosphorylation of ERK, through guinea pig ADRB1 was the same as through human ADRB1, but markedly lower than that of through rat ADRB1. ERK phosphorylation through guinea pig ADRB1 was sensitive to pertussis toxin, a dominant-negative ras and PD98059, indicating that a G(i)-mediated pathway is involved in the ADRB1/ERK signaling loop. These results suggest that the G(i)-coupling efficacy of guinea pig and human ADRB1s may be higher than that of rat ADRB1.
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Affiliation(s)
- Yoshio Tanaka
- Department of Chemical Pharmacology, Toho University School of Pharmaceutical Sciences , Funabashi-City, Chiba , Japan
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Tanaka Y, Yamashita Y, Michikawa H, Horinouchi T, Koike K. Pharmacological characterization of the β-adrenoceptor that mediates the relaxant response to noradrenaline in guinea-pig tracheal smooth muscle. Naunyn Schmiedebergs Arch Pharmacol 2007; 375:51-64. [PMID: 17237919 DOI: 10.1007/s00210-006-0130-x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2006] [Accepted: 12/18/2006] [Indexed: 11/25/2022]
Abstract
Pharmacological characteristics of beta-adrenoceptors (beta-ARs) mediating noradrenaline-induced relaxation were investigated in guinea-pig tracheal smooth muscle. The inhibitory effects of several types of beta-AR antagonists on noradrenaline-induced relaxation against histamine contraction were scrutinized with Schild plot analysis. The concentration-response curve for noradrenaline obtained in the absence of phentolamine and uptake inhibitors was competitively antagonized by all of the beta-AR antagonists used in this study (propranolol, bupranolol, atenolol, butoxamine and ICI-118,551). However, their pA2 values were markedly less than the expected values for beta1-AR and beta2-AR. On the other hand, pA2 values of ICI-118,551 (6.85) determined in the presence of phentolamine suggested a contribution of a beta1 -AR rather than beta2 -AR. In the presence of phentolamine and uptake inhibitors (desipramine and deoxycorticosterone), the Schild plot for atenolol was a better fit, with two distinct straight lines. The pA2 values of atenolol provided by the regression were: approximately 7.0, which corresponds to the expected beta1-AR value, and approximately 6.5, which was 3 times less than the expected value for beta1 -AR, and thus the possible presence of two classes of beta1 -AR (beta1(Low) and beta1(High)) was suggested. This view was also supported by Schild plot analysis for propranolol, which fit two straight lines each with a slope of 1.0. The present findings indicate that beta1 -ARs contributing to noradrenaline-elicited relaxation in guinea-pig tracheal smooth muscle exhibit diverse pharmacological characteristics and may be subdivided into at least two classes with distinct affinities for atenolol. Under physiological conditions, beta1(Low) rather than beta1(High) seems to play a more significant role in noradrenaline-regulated airway smooth muscle tone.
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Affiliation(s)
- Yoshio Tanaka
- Department of Chemical Pharmacology, Toho University School of Pharmaceutical Sciences, 2-2-1 Miyama, Funabashi-City, Chiba, 274-8510, Japan.
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Uchida K, Kamikawa Y. Muscularis mucosae - the forgotten sibling. J Smooth Muscle Res 2007; 43:157-77. [DOI: 10.1540/jsmr.43.157] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Affiliation(s)
- Kohsuke Uchida
- Department of Pharmacology, Dokkyo Medical University School of Medicine
| | - Yuichiro Kamikawa
- Department of Pharmacology, Dokkyo Medical University School of Medicine
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Tanaka Y, Horinouchi T, Koike K. New insights into beta-adrenoceptors in smooth muscle: distribution of receptor subtypes and molecular mechanisms triggering muscle relaxation. Clin Exp Pharmacol Physiol 2006; 32:503-14. [PMID: 16026507 DOI: 10.1111/j.1440-1681.2005.04222.x] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
1. The beta-adrenoceptor is currently classified into beta(1), beta(2) and beta(3) subtypes and all three subtypes are expressed in smooth muscle. Each beta-adrenoceptor subtype exhibits tissue-specific distribution patterns, which may be a determinant controlling the mechanical functions of corresponding smooth muscle. Airway and uterine smooth muscles abundantly express the beta(2)-adrenoceptor, the physiological significance of which is established as a fundamental regulator of the mechanical activities of these muscles. Recent pharmacomechanical and molecular approaches have revealed roles for the beta(3)-adrenoceptor in the gastrointestinal tract and urinary bladder smooth muscle. 2. The beta-adrenoceptor is a G(s)-protein-coupled receptor and its activation elevates smooth muscle cAMP. A substantial role for a cAMP-dependent mechanism(s) is generally believed to be the key trigger for eliciting beta-adrenoceptor-mediated relaxation of smooth muscle. Downstream effectors activated via a cAMP-dependent mechanism(s) include plasma membrane K(+) channels, such as the large-conductance, Ca(2+)-activated K(+) (MaxiK) channel. 3. Beta-Adrenoceptor-mediated relaxant mechanisms also include cAMP-independent signalling pathways. This view is supported by numerous pharmacological and electrophysiological lines of evidence. In airway smooth muscle, direct activation of the MaxiK channel by G(s)alpha is a mechanism by which stimulation of beta(2)-adrenoceptors elicits muscle relaxation independently of the elevation of cAMP. 4. The cAMP-independent mechanism(s) is also substantial in beta(3)-adrenoceptor-mediated relaxation of gastrointestinal tract smooth muscle. However, in the case of the beta(3)-adrenoceptor, a delayed rectified K(+) channel rather than the MaxiK channel seems to mediate, in part, cAMP-independent relaxant mechanisms. 5. In the present article, we review the distribution of beta-adrenoceptor subtypes in smooth muscle tissues and discuss the molecular mechanisms by which each subtype elicits muscle relaxation, focusing on the roles of cAMP and plasma membrane K(+) channels.
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Affiliation(s)
- Yoshio Tanaka
- Department of Chemical Pharmacology, Toho University School of Pharmaceutical Sciences, Funabashi-City, Chiba, Japan.
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Tanaka Y, Yamashita Y, Horinouchi T, Koike K. Adrenaline produces the relaxation of guinea-pig airway smooth muscle primarily through the mediation of beta(2)-adrenoceptors. J Smooth Muscle Res 2005; 41:153-61. [PMID: 16006748 DOI: 10.1540/jsmr.41.153] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The beta-adrenoceptor subtype that mediates adrenaline-induced relaxation was pharmacologically identified in smooth muscle cells of the isolated guinea-pig trachea. Adrenaline produced a concentration-dependent relaxation with a pD(2) value of 7.1. The concentration-response curve for adrenaline was shifted rightwards in a competitive fashion by the beta(1)-/beta(2)-nonselective antagonists propranolol and bupranolol, with pA(2) values of 8.85 and 8.97, respectively. Adrenaline-induced relaxation was not affected by the beta(1)-selective antagonists atenolol and CGP-20, 712A within the concentration ranges supposed to antagonize the beta(1)-subtype (atenolol, <or=10(-6) M; CGP-20, 712A, <or=10(-8) M). By contrast, the concentration-response curve for adrenaline was shifted rightwards in a competitive fashion by atenolol at concentrations >or=3x10(-6) M with a pA(2) value of 5.77. The concentration-response curve for adrenaline was also competitively antagonized by the beta(2)-selective antagonists butoxamine and ICI-118,551 with pA(2) values of 6.86 and 8.73, respectively. The pA(2) values of beta-adrenoceptor antagonists (propranolol, bupranolol, atenolol, butoxamine and ICI-118,551) tested against adrenaline were consistent with the values when tested against salbutamol, a beta(2)-selective adrenoceptor agonist. The present findings provide evidence that the relaxant response of the smooth muscle of the guinea-pig trachea to the adrenal medulla hormone, adrenaline, is mainly mediated through beta(2)-adrenoceptors.
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Affiliation(s)
- Yoshio Tanaka
- Department of Chemical Pharmacology, Toho University School of Pharmaceutical Science, Miyama 2-2-1, Funabashi-city, Chiba 274-8510, Japan.
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Tanaka Y, Yamashita Y, Horinouchi T, Yamaki F, Koike K. Evidence showing that beta-adrenoceptor subtype responsible for the relaxation induced by isoprenaline is principally beta2 but not beta1 in guinea-pig tracheal smooth muscle. ACTA ACUST UNITED AC 2004; 24:37-43. [PMID: 15458542 DOI: 10.1111/j.1474-8673.2004.00314.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
1. The present study was carried out to pharmacologically identify the beta-adrenoceptor subtype that mediates isoprenaline-elicited relaxation in the isolated guinea-pig tracheal smooth muscle, to answer the question whether it is beta(1)- or beta(2)-subtype? 2. Isoprenaline as well as salbutamol, a well-known beta(2)-selective adrenoceptor agonist, produced a concentration-dependent relaxation with a pD(2) value of 8.12 vs. 7.54 for salbutamol. 3. Isoprenaline-elicited relaxation was not affected by beta(1)-selective antagonists, atenolol and CGP-20,712A, within the concentration ranges supposed to antagonize beta(1)-subtype: atenolol, < or =10(-6) M; CGP-20,712A, < or =10(-8) M. 4. By contrast, the concentration-response curves for isoprenaline as well as salbutamol were shifted rightwards in a competitive fashion by atenolol at the concentrations > or =3 x 10(-6) M. However, pA(2) values of atenolol against isoprenaline (5.86) and salbutamol (5.71) were consistent with the value corresponding to beta(2)- but not to beta(1)-subtype (around 7.00), and these values were not significantly different from each other. 5. Competitive antagonism of the relaxations to isoprenaline and salbutamol were also obtained with beta(2)-selective antagonists, butoxamine and ICI-118,551. Against isoprenaline and salbutamol, the pA(2) values of butoxamine (6.51 vs. 6.81) and ICI-118,551 (8.83 vs. 8.90) were substantially identical. Thus the primary mediation of beta(2)-receptor in the relaxations was strongly supported. 6. The present findings provide evidence that the beta-adrenoceptor which mediates isoprenaline-elicited relaxation of guinea-pig tracheal smooth muscle is essentially beta(2)- but not beta(1)-subtype. The present study also indicates the importance of using multiple receptor antagonists with different pA(2) values to pharmacologically identify the responsible receptor subtype in smooth muscle mechanical responses.
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Affiliation(s)
- Y Tanaka
- Department of Chemical Pharmacology, Toho University School of Pharmaceutical Sciences, Miyama 2-2-1, Funabashi-City, Chiba 274-8510, Japan
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