Localization of β 2-adrenoceptor messenger RNA in human and rat lung using in situ hybridization: Correlation with receptor autoradiography

Abstract

We have used in situ hybridization to study the localization of mRNA encoding the β 2-adrenoceptor in tissue sections of the human and rat lung and compared this with the distribution of β 2-receptor binding sites using receptor autoradiography. To localize β 2-receptor mRNA, a [ 32P]labeled antisense RNA probe (riboprobe) was generated from human or rat β 2-receptor cDNA. A similar distribution of β 2-receptor mRNA was identified in both species. The highest intensity of β 2-receptor mRNA was detected in smooth muscle of small airways, airway epithelium and pulmonary blood vessels. Lower intensity of β 2-receptor mRNA was identified in smooth muscle of large airways, and alveolar epithelium (presumably type I and type II pneumocytes). No significant hybridization signal was detected in interstitial tissue. The specificity of the hybridization signal was confirmed with a sense probe (having identical sequence to the mRNA) and preincubation with RNase A, and by Northern blot analysis which revealed a single band of mRNA of 2.2 kb. There was a correspondence between mRNA localization and the distribution of β 2-receptors visualized by [ 125I]iodocyanopindolol autoradiographically in the presence of CGP 20712 (a β 1-selective antagonist). However, alveolar walls that showed a high β 2-receptor density had relatively low levels of mRNA. This cellular heterogeneity may reflect differences in RNA stability or transcription rate in different lung cells. This approach opens up new options in the investigation of the regulation of pulmonary β 2-receptor gene expression in health and disease.