Fig. 3. Quantification of GST-Grp1-PH labeling over cellular membranes after PDGF stimulation. Ultrathin cryosections of PDGF-stimulated Swiss 3T3 cells were labeled with GST-Grp1-PH and the labeling over cellular membranes was quantified as described previously (Watt et al., 2002). The proportions of GST-Grp1-PH labeling over individual compartments by on-section labeling are shown in A as percentages of the total gold particles counted, estimated by scanning cell profiles and assigning gold particles to compartments. The results are the means for three independent experiments, in which 1350-2100 gold particles were counted per experiment. The labeling densities over membrane compartments are shown in B, in which the number of gold particles were related to the number of intersections a scanning line makes with membranes from each compartment, as described by Watt et al. (Watt, et al., 2002). The results shown are one representative data set from three individual experiments, in which 839-1643 intersections and 1598-2643 gold particles were counted per experiment. Nuclear densities from a representative experiment, expressed as the number of gold particles related to area, are shown in the inset. Data are the means from an experiment in which 1342 gold particles were counted. Asterisks over the MVB and MLE columns indicate that the data were derived using intersections through the outer membrane and adjusted appropriately, as described (Watt et al., 2004). Error bars in A and B represent s.e.m. CYT, cytosol; ER, endoplasmic reticulum; GOL ST, Golgi stack; GOL VES, Golgi vesicles; LAM, lamellipodia; LYS, lysosome; MIT IN, mitochondria inner membrane; MLE, multilamellar body; MVB, multivesicular body; MIT OUT, mitochondria outer membrane; NUC, nucleus; NUC ENV, nuclear envelope; PM, plasma membrane; UN, unassigned (gold particles associated with indistinct structures).