Reexamination of the Fine Structure of the Pancreatic Duct System in the Rat: a Proposal of Morphological Segmentation

Abstract

The pancreatic duct system is generally regarded as a uniform conduit lined by principal cells that secrete bicarbonate-rich fluid. However, previous studies have suggested the morphological and functional heterogeneity of these cells. We reexamined the fine structure of the principal cells in the rat pancreas by both scanning electron microscopy after exposure of the cells with NaOH maceration, and by transmission electron microscopy according to a conventional method. The specimen was also observed by immunohisochemistry with a monoclonal antibody OS-3 recognizing the renal type B intercalated cell. The ducts in the rat pancreas were lined by a simple epithelium devoid of basal cells, and arborized dichotomously. The duct system consisted of two parts: a fine proximal duct and thicker distal duct. Principal cells in the latter, as compared with those in the former, displayed relatively numerous microplicae on the basolateral membrane and abundant mitochondria in the cytoplasm. The distal duct cells were also unique in their possessing secretory canaliculi opening into the main lumen as well as thick lateral processes for cellular interdigitation. These findings suggest that the distal duct has a greater ability to transport ions than does the proximal one. The antibody OS-3 preferentially labeled the distal duct cells, augmenting their distinction from the proximal duct cells.