Modulation of -Adrenoreceptor Expression in the Airways

β-Adrenoceptors (βAR) are members of the G-protein-coupled receptor superfamily, consisting of three subtypes: β₁ , β₂ , and β₃ (1 ). cDNAs and genes encoding three subtypes have been cloned from several species, including human. There are only β₁ - and β₂ ARs to be found in lung (2 ), which regulate many aspects of lung function. In addition to desensitization and downregulation at the cell surface membrane, the number of βARs expressed is modulated by regulation of steady-state levels of mRNA and the rate of gene transcription (3 ). Regulation of β- and β₂ AR mRNAs and gene transcription in lung may occur after exposure to receptor agonists or drug treatments (4 –6 ). Thus, this could represent a mechanism for long-term modulation of βAR expression.