初代培養肺胞II型上皮細胞に発現するβ_1-およびβ_2-adrenoceptor mRNA量の変化 Changes in β_1-and β_2-adrenoceptor mRNA levels in alveolar type II cells during cultivation
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 <I>in vitro</I> 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 β<SUB>1</SUB> and β<SUB>2</SUB>-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 β<SUB>1</SUB>- and β<SUB>2</SUB>-adrenoceptor in cultured type II cells by a quantitative RNase protection assay, developed by us.<BR> The mRNA levels for β<SUB>1</SUB> and β<SUB>2</SUB>-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 β<SUB>1</SUB> mRNA level was remarkably reduced. Dexamethasone treatment of 24 h-cultured cells caused increase in the level of β<SUB>2</SUB>-adrenoceptor mRNA, without changing that of β<SUB>1</SUB> 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.
日本薬理学雑誌 106, 112-116, 1995-09-01