Spontaneous activation of β2- but not β1-adrenoceptors expressed in cardiac myocytes from β1β2 double knockout mice

Ying Ying Zhou, Dongmei Yang, Wei Zhong Zhu, Sheng Jun Zhang, Ding Ji Wang, Dan K. Rohrer, Eric Devic, Brian K. Kobilka, Edward G. Lakatta, Heping Cheng, Rui Ping Xiao

Research output: Contribution to journalArticle

Abstract

Although ligand-free, constitutive β2-adrenergic receptor (AR) signaling has been demonstrated in naive cell lines and in transgenic mice overexpressing cardiac β2-AR, it is unclear whether the dominant cardiac β-AR subtype, β1-AR, shares the ability of spontaneous activation. In the present study, we expressed human β1- or β2-AR via recombinant adenoviral infection in ventricular myocytes isolated from β1β2-AR double knockout mice, creating pure β1-AR and β2-AR systems with variable receptor densities. A contractile response to a nonselective β-AR agonist, isoproterenol, was absent in double knockout mouse myocytes but was fully restored after adenoviral β1-AR or adenoviral β2-AR infection. Increasing the titer of adenoviral vectors (multiplicity of infection 10-1000) led to a dose-dependent expression of β1- or β2-AR with a maximal density of 1207 ± 173 (36-fold over the wild-type control value) and 821 ± 38 fmol/mg protein (69-fold), respectively. Using confocal immunohistochemistry, we directly visualized the cellular distribution of β1-AR and β2-AR and found that both subtypes were distributed on the cell surface membrane and transverse tubules, resulting in a striated pattern. In the absence of ligand, β2-AR expression resulted in graded increases in baseline cAMP and contractility up to 428% and 233% of control, respectively, at the maximal β2-AR density. These effects were specifically reversed by a β2-AR inverse agonist, ICI 118,551 (10-7 M). In contrast, overexpression of β1-AR, even at a greater density, failed to enhance either basal cAMP or contractility; the alleged β1-AR inverse agonist, CGP 20712A (10-6 M), had no significant effect on basal contraction in these cells. Thus, we conclude that acute β2-AR overexpression in cardiac myocytes elicits significant physiological responses due to spontaneous receptor activation; however, this property is β-AR subtype specific because β1-AR does not exhibit agonist-independent spontaneous activation.

Original languageEnglish (US)
Pages (from-to)887-894
Number of pages8
JournalMolecular Pharmacology
Volume58
Issue number5
DOIs
StatePublished - Jan 1 2000
Externally publishedYes

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ASJC Scopus subject areas

  • Molecular Medicine
  • Pharmacology

Cite this

Zhou, Y. Y., Yang, D., Zhu, W. Z., Zhang, S. J., Wang, D. J., Rohrer, D. K., Devic, E., Kobilka, B. K., Lakatta, E. G., Cheng, H., & Xiao, R. P. (2000). Spontaneous activation of β2- but not β1-adrenoceptors expressed in cardiac myocytes from β1β2 double knockout mice. Molecular Pharmacology, 58(5), 887-894. https://doi.org/10.1124/mol.58.5.887