γ-Aminobutyric acid type-A (GABA_A) receptor is expressed in alveolar type II (ATII) cells. (A) Typical images of double staining of mouse lung tissues for presurfactant protein C (PSPC; red) and the α2 subunit of GABA_A receptor (green). (B) Representative images of double staining of human lung tissue for PSPC (green) and the π subunit of GABA_A receptor (red). The images in A and B are at the same magnification. (C) Illustrative immunofluorescent image of β2 and/or β3 subunits of GABA_A receptor (green) in ATII cells under nonpermeabilized conditions, which reveals the presence of GABA_A receptor in the cell membrane surface. Propidium iodide (red) was used to stain the cell nuclei. (D) Immunoblots showing expression of five GABA_A receptor subunit proteins in A549 cells. Lysate of mouse cortex was used as a positive control for GABA_A receptor subunits, except the π subunit, for which the positive control was lysate of Jurkat cells.