Abstract
(-)-Isoproterenol [4-[1-hydroxy-2-[(1-methylethyl)amino]ethyl]-1,2-benzene diol hydrochloride] relaxes murine detrusor through β-adrenoceptors (ARs); however, the β-AR subtypes involved are unknown. β2-ARs have been associated with caveolae, plasma-lemmal scaffolding domains that are absent in caveolin-1 (cav-1) knockout (KO) mice. Here, we studied detrusor responses in the absence and presence of β-AR subtype-selective antagonists in wild-type (WT) and cav-1 KO mice. To inquire whether the murine detrusor model is relevant to man, β-AR subtypes that mediate (-)-isoproterenol-evoked human detrusor relaxation were investigated. In WT mice, (-)-isoproterenol concentration-dependently relaxed the KCl (40 mM)-precontracted detrusor (-logEC50M = 8.04, Emax = 62%). The effects of (-)-isoproterenol were surmountably antagonized by the β2-AR-selective antagonist ICI 118,551 [(±)-1-[2,3-(dihydro-7-methyl-1H-inden-4-yl)oxy]-3-[(1-methylethyl)amino]-2-butanol] (pKB = 9.28) but not affected by the β1-AR-selective antagonist CGP 20712 [1-[2-((3-carbamoyl-4-hydroxy)phenoxy)ethylamino]-3-[4-(1-methyl-4-trifluoromethyl-2-imidazolyl)phenoxy]-2-propanol] and β3-AR-selective L-748,337 [(S)-M-[4-[2-[3-[3-[acetamidomethyl)phenoxy)-2-hydroxypropyl]-amino]-ethyl]-phenylbenzsulfonamide)], suggesting involvement of β2-AR only. The cav-1 KO detrusor displayed significant contractile dysfunction. (-)-Isoproterenol was less potent and efficient in relaxing detrusor from cav-1 KO (-logEC50M, 7.76; Emax = 44%), but ICI 118,551 caused similar antagonism (pKB = 9.15), suggesting that β2-AR function persisted in cav-1 KO. The β3-AR-selective antagonist L-748,337 in the presence of ICI 118,551 and CGP 20712 caused additional blockade of (-)-isoproterenol effects in cav-1 KO, consistent with a β3-AR involvement during relaxation and suppression of this effect in WT. (-)-Isoproterenol relaxed human detrusor muscle precontracted with carbachol (-logEC50M = 6.39, Emax = 52%). However, the effects of (-)-isoproterenol in human detrusor were not blocked by CGP 20712 or ICI 118,551 but antagonized by L-748,337 (pKB = 7.65). We conclude that murine detrusor relaxation occurs via β2-AR, and loss of caveolae does not perturb β2-AR function but unmasks an additional activation of β3-AR. In contrast, detrusor relaxation in man is mediated exclusively via β3-AR.
Footnotes
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Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
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doi:10.1124/jpet.108.142562
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ABBREVIATIONS: AR, adrenoceptor; cav-1, caveolin-1; KO, knockout; RT, reverse transcriptase; PCR, polymerase chain reaction; WT, wild type; L-748,337 (S)-M-[4-[2-[3-[3-[acetamidomethyl)phenoxy)-2-hydroxypropyl]-amino]-ethyl]-phenylbenzsulfonamide); ICI 118,551, (±)-1-[2,3-(dihydro-7-methyl-1H-inden-4-yl)oxy]-3-[(1-methylethyl)amino]-2-butanol; CGP 20712, 1-[2-((3-carbamoyl-4-hydroxy)phenoxy)ethylamino]-3-[4-(1-methyl-4-trifluoromethyl-2-imidazolyl) phenoxy]-2-propanol; phentolamine hydrochloride, 2-[N-(3-hydroxyphenyl)-p-toluidinomethyl]-2-imidazolidine hydrochloride; CHO, Chinese hamster ovary; BRL 37,344, (±)-(R*,R*)-[4-[2-[[2-(3-chlorophenyl)-2-hydroxyethyl]amino]propyl]phenoxy]acetic acid; L-755,507, 4-[[hexylamino)carbonyl]amino]-N-[4-[2-[[(2S)-2-hydroxy-3-(4-hydroxyphenoxy)propyl]amino]ethyl]-benzenesulfonamide; SR 59,230, 1-(2-ethylphenoxy-3-[[(1S)-1,2,3,4-tetrahydro-1-naphthalenyl]amino]-(2S)-2-propanol hydrochloride.
- Received June 23, 2008.
- Accepted September 25, 2008.
- The American Society for Pharmacology and Experimental Therapeutics
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