Structure of the Walls of the Bile ‘Canaliculi’ in Mammalian Liver Cells

Abstract

THE structure of the walls of the bile canaliculi of the liver has long been of interest; the question of importance being whether the canaliculi had definite walls of their own, or whether they were formed from modifications of the walls of the hepatocytes themselves. Early workers^1–3 believed that the canaliculi had definite walls of their own; but Zimmermann⁴ suggested that they were formed by modifications of the walls of the hepatocytes, and described dense structures at the edges of the canaliculi which he called “terminal bars”. Morton⁵ was able to show that the lining of the bile canaliculi was in the form of a ‘brush border’, and apart from Zimmermann's terminal bars he found a collection of basophilic material in the cell cytoplasm lying close to the bile ducts. Rouiller⁶, in an electron microscope study of the rat liver bile canaliculi, showed that the cell membranes were closely opposed in the neighbourhood of the canaliculus, but with only osmium as an electron stain, he found no modification or thickenings of the cell wall in the proximity of the duct. In a study of normal and regenerating rat liver using ‘Araldite’ embedding followed by phosphotungstic acid staining, it was found that some parts of the cell walls related to the bile ducts took up this stain particularly well.