Morphologic characterization of secretory pods visualized by TEM. (A) Low magnification view showing a cluster of SPs and WPBs (white asterisks). Some WPBs have rounded up (black asterisks). (B) An SP displaying a core of lacy material that is connected to the delimiting membrane of the SP by short filaments (open arrowheads). A WPB (white asterisk) makes contact with the SP (bottom left). A rounded WPB (black asterisk) displays an electron lucent area interposed between the delimiting membrane and the matrix (small arrow). (C) A clathrin-coated vesicle (small arrow) is connected to the secretory pod (SP) by a small neck. Note that the WPB labeled with the white asterisk has a denser content than the WPB indicated with an arrowhead. (D) Another example of an SP displaying signs of membrane retrieval (clathrin-coated pit, arrow) and in close contact with a WPB (white asterisk). Note that the membrane of the WPB is electron denser at the interface with the SP, while the delimiting membrane of the SP appears “zippered up” to the WPB. Scale bars represent 100 nm. Images were acquired with an FEI Tecnai 12 TEM at 120 kV and using an FEI Eagle 4kx4k CCD camera.