Fig. 1.

Expression of the insulin receptor and activation of PI3 kinase in L cells. A, Semiquantitative RT-PCR analysis for insulin receptor mRNA transcripts in GLUTag (a: lane 2) and NCI-H716 cells (c: lane 2). Mouse fat (a: lane 3) and human placenta (c: lane 3) were used as positive controls, respectively, whereas the omission of template RNA was used as negative controls (a: lane 1, c: lane 1). Murine GLUTag (b) and human NCI-H716 (d) cells were subjected to immunofluorescent staining for the insulin receptor β-subunit (red); 4′,6′-diamino-2-phenylindole (DAPI; blue) was used to visualize nuclei. B, Mouse (a–f) and human (g–l) intestinal sections and FRIC cultures (m–r) were subjected to double-immunofluorescent staining for the insulin receptor α-subunit (green) and GLP-1 (red); DAPI (blue) was used to visualize nuclei. The absence of primary antisera was used as negative controls (mouse: a–c; human: g–i; FRIC: m–o). Arrowheads indicate L cells, and arrows indicate basolateral staining for the insulin receptor α-subunit. Colocalization of the insulin receptor and GLP-1is indicated by yellow in the overlay (f, l, and r). C, Immunofluorescent detection of PIP₃ production (red) in response to treatment of GLUTag cells with media alone (a) or 10⁻⁷ m insulin (b) for 5 min. Identical camera exposure times were used. Scale bars, 10 μm.