Cellular localization of intracellular oligomers in hIAPP cells. Immunogold labeling for oligomers in hIAPP-non-expressing cells (control) (panels a, b, and b′) and hIAPP-expressing cells (hIAPP cells) (panels c, d, and d′) is shown; panels b′ and d′ were enlargements of panels b and d, respectively. Oligomers were only detected in hIAPP cells in the ER (arrows in panel d′), in insulin granules (IG) (arrow in panel d), and associated to the plasma membrane (PM) (arrow in panel c). Bars are 0.2 μm. *, p < 0.05 versus control cells.