Figure 7. PD counting on serial sections.

A. Cartoon depicts 4 serial sections on a grid. Structures of interest are spotted on the reference section n and then followed on look-up sections n + 1, n + 2 etc. When structure cannot be seen anymore, it is said to be resolved. (B-C) Micrographies of 90 nm thick sections of a type I PD (left) and type II (PD) typically collected for quantification. Membranes of the pores are visible, and they connect with both sides. In the latter, heterogeneous densities inside the pore allow the visualization of cytoplasmic sleeve space (white arrows). Although not as resolutive as tomography, the central element (desmotubule) can be seen spanning the pore in the center.