Functional and molecular evidence for β1-, β2- and β3-adrenoceptors in human colon

S. J. Roberts, M. Papaioannou, B. A. Evans, R. J. Summers

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44 Citations (Scopus)

Abstract

1. Relaxation of carbachol pre-contracted human colonic muscle to (-)-isoprenaline was examined in circular, longitudinal and taenia coli preparations to determine the β-adrenoceptor subtypes involved. β1-, β2- and β3-Adrenoceptor mRNAs were also measured in colonic muscle and mucosa. 2. (-)-Isoprenaline caused relaxation of longitudinal smooth muscle preparations with pEC50 = 7.39 ± 0.12, and this response was inhibited by both propranolol (0.1 μM, pK(B) 8.55 ± 0.12) and the selective β1-antagonist, CGP 20712A (0.1 μM, pK(B) 8.80 ± 0.20), while the selective β2-antagonist, ICI 118551 (0.1 μM) failed to inhibit isoprenaline relaxation consistently. 3. (-)-Isoprenaline caused relaxation of taenia coli with a pEC50 of 6.70 ± 0.17. Propranolol (0.1 μM), CGP 20712A (0.1 μM) and ICI 118551 (0.1 μM) inhibited the isoprenaline response with similar low affinities (pK(B) values 7.93, 7.71 and 7.54, respectively). Carbachol pre-contracted circular smooth muscle preparations failed to relax consistently to isoprenaline and these responses were not characterized. 4. β1- and β2-Adrenoceptor mRNAs were present in circular/longitudinal muscle samples and taenia coli samples, and lower levels were detected in mucosa. β3-mRNA was also present in both muscle preparations but was not detected in human colonic mucosa. 5. In summary, β1-adrenoceptors are the predominant subtype mediating isoprenaline-induced relaxation of the thin longitudinal smooth muscle of human colon, while β3-receptors do not appear to be involved in these responses. However, β3-adrenoceptors may play a role in relaxation of the taenia coli as conventional antagonist affinities are low. β3-Adrenoceptor mRNA was present in taenia coli and circular/longitudinal smooth muscle but absent from human colonic mucosa.

Original languageEnglish
Pages (from-to)1527-1535
Number of pages9
JournalBritish Journal of Pharmacology
Volume120
Issue number8
DOIs
Publication statusPublished - 1 Jan 1997
Externally publishedYes

Keywords

  • Human colon
  • Messenger RNA
  • Mucosa
  • Smooth muscle
  • β-adrenoceptors

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