For conventional TEM, cells were fixed in 2.5% glutaraldehyde in 0.1 M cacodylate buffer (pH 7.2) for 1.5 hr at room temperature and post-fixed with 1% osmium tetroxide in 0.1 M cacodylate buffer (pH 7.2) for 1 hour at room temperature. Then cells were embedded in 2% agarose and cell blocks were post-fixed with 2% uranyl acetate in 30% ethanol, dehydrated in graded series of ethanol and embedded in epoxy resin. Ultrathin sections were cut with a Leica Ultramicrotome UCT (Leica Microsystems; Vienna, Austria) and collected on 400-mesh formvar coated copper grids. Sections were stained 45 minutes with 4% aqueous uranyl acetate and 5 minutes with lead citrate.