Cellular Channels. The intranuclear channels in a range of cell types contain nuclear pore complexes and are associated with an electron dense halo in the nucleoplasm. Representative profiles of channels from 3T3 cells (a), NRK cells (b), A431 cells (d and inset), and HeLa cells (f) are shown. Double membrane structures are clearly visible, together with local fenestrations, and comparable to the appearance of the nuclear pore complexes in the nuclear envelope of the 3T3 nucleus shown in e. The electron lucent core is also seen to contain small circular or crescent shaped features, best seen within the channel in b. Electron dense material in the nucleoplasm is associated with the channels (a, b and d, inset). In addition, channel association with nucleoli is shown for NRK cells (b). Thawed frozen thin section colloidal gold immunocytochemistry confirms that the channels are associated with strong immunoreactivity for lamins (c) and protein disulphide isomerase (f), as shown by the 9-nm gold particles decorating the intranuclear channels in these HeLa nuclei. Bars: 200 nm; d, 1 μm. Interphase nuclei of many mammalian cell types contain deep, dynamic, tubular membrane-bound invaginations of the nuclear envelope. Fricker M, Hollinshead M, White N, Vaux D - The Journal of cell biology (1997). Not Altered. CC.