A – Illustration of another surface membrane pattern of an SR-BI-V5 transfected Y1-BS1 cell revealing undulating double membraned channels (arrowheads). Such channel membranes are open to the cell surface (arrow) and dip into the cell where they encircle patches of cytoplasm. B – The surface of a cortical cell from the adrenal of an ACTH treated rat processed by standard (non-immunochemical) procedures . The surface of this cell illustrates the similarity between the double membraned surface structures of normal hormone-stimulated adrenocortical cells with those formed in SR-BI transfected cells -as shown in Fig. 3A. Note, that in this normal adrenal cell, the double membraned channels also open to the cell surface (arrows). Striations within the channels (arrowheads) identify lipoproteins .