Novel volume‐electron microscopic ultrastructural analysis of gastrointestinal excitability associated with calcium–activated chloride channels

-dependent mechanisms. Novel volume-electron microscopy (EM) techniques, such as focused ion beam/scanning electron microscopy (FIB/SEM), are powerful tools to understand these mechanisms. These techniques can show cellular membrane contacts in sheet structures, and can calculate geometrical features, such as distance, surface area and volume. Geometric analysis of organelles and membranes with FIB/SEM represents a novel study of the gastrointestinal tract. Conventional transmission EM images and immunohistochemistry of new ICC subtypes are reviewed with respect to the relationship between anatomical and physiological functions. 3-D analysis of endoplasmic reticulum in motor neurons is also summarized as an example of other excitable cell types analysed by FIB/SEM.