Cells were pelleted (five minutes, 2086g), resuspended in 1 mL PBS, and pelleted again (five minutes, 2086g). Supernatant was removed and 2.5% glutaraldahyde solution (adjusted to pH 7.4 using HCl and to 400 mOsm using CaCl 2 ) added. Samples were processed and imaged by Dr. Gary Mierau, The Children's Hospital Department of Pathology/Laboratory Services, Aurora, CO. Briefly, samples were post-fixed in 2% cacodylate buffered osmium tetroxide (pH 7.4), dehydrated in a graded series of alcohols, and embedded in epoxy resin. Sections, approximately 80 nm in thickness, were stained with uranyl acetate and lead citrate prior to examination at 60 kV with a Zeiss EM-10 transmission electron microscope (Carl Zeiss Inc, Thornwood, NY).