Phenotypic control of gap junctional communication by cultured alveolar epithelial cells

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Abstract
We examined phenotype-specific changes in gap junction protein [connexin (Cx)] expression and function by cultured rat alveolar type II cells. Type II cells cultured on extracellular matrix in medium containing keratinocyte growth factor (KGF) and 2% fetal bovine serum (FBS; KGF/2) retained expression of surfactant protein C and the 180-kDa lamellar body membrane protein (lbm180). These markers were lost when cells were cultured in medium containing 10% FBS (MEM/10). With RT-PCR, cells cultured in MEM/10 showed transient increases in Cx43 and Cx46 mRNA expression, whereas Cx32 and Cx26 decreased and Cx30.3 and Cx37 were unchanged. Transient changes in Cx32, Cx43, and Cx46 protein expression were confirmed by immunoblot. In contrast, cells cultured in KGF/2 retained expression of Cx32 and showed increased expression of Cx30.3 and Cx46 mRNAs, compared with that in day 0 cells. With immunofluorescence microscopy, Cx32 and Cx43 were at the plasma membrane of cells grown in KGF/2, whereas Cx46 was exclusively intracellular. Type II cells cultured in MEM/10 showed ∼3- to 4-fold more intercellular transfer of microinjected lucifer yellow through gap junctions than cells grown in 2% FBS. Thus type II cells dynamically alter gap junctional communication, and distinct alveolar epithelial cell phenotypes express different connexins.