Fig. 1. InsP₃R expression and localization. (A) The histograms illustrate the relative abundances of the three InsP₃R isoforms in the cell types listed. The data were obtained by analysing the density of the immunoreactive bands at 260 kDa. The data show means±s.e.m. of three blots. (B) Typical confocal images (z depth <1 µm) of (left) HeLa cells stained for type 1 InsP₃Rs, (middle) HUVEC cells stained for type 2 InsP₃Rs and (right) 16HBE14o- cells stained for type 3 InsP₃Rs. In most of the cell types, a reticular distribution of staining could be observed but, in 16HBE14o- cells in particular, the ER seemed to be considerably fragmented after fixation. (C) Intensity profiles of immunofluorescence from the nuclear envelope to the plasma membrane. These profiles were obtained by sampling the immunofluorescence intensity of the major InsP₃R isoform in each cell type across a line one pixel wide running from the nuclear envelope to the plasma membrane.