Contribution of cryoelectron microscopy of vitreous sections to the understanding of biological membrane structure.

Using cryoelectron microscopy of vitreous sections, we investigated in situ the ultrastructure of biological membranes, selected from several cell types for their diverse biological functions. Here we describe how to visualize the two membrane leaflets and tightly apposed membranes, lying as close as 1.1 nm apart, by tuning the imaging conditions. We show how defects in membrane stacks may be clues to resolving their structure. Details of membrane proteins are also resolved, as well as protein lattices with correlations between stacked membranes. Imaging the cell in its native hydrated state can now be done in the nanometer resolution range, which should open unique routes for investigating structure-function relationships.