Figure 4

Insulin and IGF-I translocate TRPV1 to the plasma membrane. a, Potentiation of saturating concentrations of capsaicin response by insulin and PDBu. Application of 5, 10 and 20 μM capsaicin shows saturation of current response (a _i ), exposure (2–5 min) of insulin (a _ii ) or PDBu (a _iii ) caused a 50% increase in current amplitude induced by 20 μM capsaicin (a _iv ) (insulin n = 4 P < .01; PDBu n = 5 P > .01). b, Representative Western blot of surface protein and total TRPV1 from control and insulin-treated (10 μM, 15 min) HEK293 cells expressing TRPV1 (probed with anti-TRPV1 antibody). Surface represents fraction of biotinylated TRPV1 and total represents total amount of TRPV1 in immunoprecipitate. Quantitative analysis of insulin's effect on surface expression, with mean densities of surface bands normalized to control values for samples run on the same gel (n = 4, P < .01). c, Immunohistochemistry performed TRPV1 transfected HEK cells that were exposed to IGF-I (20 nM, 15 min), insulin (10 μM, 15 min) and PKC agonist, PDBu (10 μM, 15 min). Quantification of relative optical intensities (ROI, normalized as surface/cytosol for each cell): (control: n = 5; IGF-I: n = 7, P < .05; insulin: n = 3 P < .01; and PDBu: n = 7, P < .01). d, Confocal image showing a significant increase (3.17 ± 0.52 fold, n = 9; P < .01) in fluorescence intensity at the membrane 5 min after exposure to IGF-1 (50 nM) in HEK cells heterologously expressing GFP-TRPV1 fusion protein as compared to before IGF-1 application.