初代培養肺胞II型上皮細胞に発現するβ<SUB>1</SUB>-およびβ<SUB>2</SUB>-adrenoceptor mRNA量の変化

Abstract

Alveolar type II cells synthesize and secrete pulmonary surfactant. Type II cells maintained on tissue culture plastic lose their diffrentiated functions and become flattened like alveolar type I cells. This phenotypic change observed in these cells in vitro has been suggested to represent differentiation of type II cells to type I cells. However, the analysis of this phenotypic progression demands specific functional markers to both cells. We have previously reported that both β1 and β2-adrenoceptors coexist in type II cells and both receptors are involved in pulmonary surfactant secretion. In some cell types the expression levels of β-adrenoceptor mRNAs change with a process of cell differentiation. In this study, therefore, we determined the levels of mRNA for β1- and β2-adrenoceptor in cultured type II cells by a quantitative RNase protection assay, developed by us. The mRNA levels for β1 and β2-adrenoceptors in the freshly isolated cells were 0.51 ± 0.07 and 1.92 ± 0.19 amol/μg total cellular RNA, respectively. These values did not change after 24 h-culture. However, in the over 48 h-cultured cells, which failed to synthesize and secrete pulmonary surfactant, only β1 mRNA level was remarkably reduced. Dexamethasone treatment of 24 h-cultured cells caused increase in the level of β2-adrenoceptor mRNA, without changing that of β1 mRNA. These results suggest that each mRNA expression may be separately regulated in cultured alveolar type II cells. The expression levels of these adrenoceptor mRNAs may be useful as a new marker in the investigation of alveolar epithelial cell differentiation.