Fig. 2. High power electron micrograph through a typical parietal cell. Microvilli project into the lumina of the canaliculi (can). Endocytic activity is commonly seen at the canalicular surface (arrows). Numerous membrane profiles of H,K-ATPase-rich structures (arrowheads), most of which appear tubular and vesicular in thin section, are located in spaces between the mitochondria (m). Bar, 1 µm.