The endolymphatic duct and sac of the rat: a histological, ultrastructural, and immunocytochemical investigation

Abstract

A study of the ultrastructure, vascularization, and innervation of the endolymphatic duct and sac of the rat has been performed by means of light- and electron-microscopic and immunocytochemical methods. Two different types of epithelial cells have been identified: the ribosome-rich cell and the mitochondria-rich cell. These two cell types make up the epithelium of the complete endolymphatic duct and sac, although differences in their quantitative distribution exist. The morphology of the ribosome-rich cells varies between the different parts of the endolymphatic duct and sac; the morphology of the mitochondria-rich cells remains constant. According to the epithelial composition, vascularization, and structural organization of the lamina propria, both duct and sac are subdivided into three different parts. A graphic reconstruction of the vascular network supplying the endolymphatic duct and sac shows that the vascular pattern varies among the different parts. In addition, the capillaries of the duct are of the continuous types, whereas those supplying the sac are of the fenestrated type. Nerve fibers do not occur within the epithelium of the endolymphatic duct and sac. A few nerve fibers regularly occur in the subepithelial compartment close to the blood vessels; these fibers have been demonstrated in whole-mount preparations by the application of the neuronal marker protein gene product 9.5. Single beaded fibers immunoreactive to substance P and calcitonin-gene related peptide are observed within the same compartment. Dopamine-beta-hydroxylase-immunoreactive axons are restricted to the walls of arterioles. Morphological differences between the different portions of the endolymphatic duct and sac are discussed with regard to possible roles in fluid absorption and immunocompetence.

Localization and Functional Studies of Pendrin in the Mouse Inner Ear Provide Insight About the Etiology of Deafness in Pendred Syndrome

“…Pendrin was detected in the apical membrane of cells that protrude slightly into the lumen ( Fig. 3a-d); these cells might correspond to the mitochondriarich cells (or light cells) described previously (Dahlmann and von During 1995;Furuta et al 1991;Lundquist 1976). This membrane is populated with abundant microvilli that show significant immunoreactivity with the anti-pendrin antibody (data not shown).…”

“…Perhaps the function of pendrin in the endolymphatic sac is to maintain the ionic and/or pH homeostasis between these two compositionally distinct fluids. It is interesting to note that there are ultrastructural similarities between the epithelia of the renal collecting duct [where pendrin is involved in bicarbonate transport ] and the inner-ear endolymphatic sac (Dahlmann and von During 1995;Peters et al 2002).…”

Soluble Megalin Is Accumulated in the Lumen of the Rat Endolymphatic Sac

“…In the ES, there are two types of epithelial cell, i.e., the mitochondria-rich cell (also called the light cell or the type-1 epithelial cell) and the ribosome-rich cell (also called the dark cell or the type-2 epithelial cell) (Lundquist, 1965;Fukazawa et al, 1990;Dahlmann and von During, 1995). The ES lumen contains a viscous endolymph including macromolecular complexes such as proteoglycans; however, the precise composition of the material is not fully understood (Friberg et al, 1986;Hultcrantz et al, 1997).…”

The Detailed Localization Pattern of Na+/K+/2Cl− Cotransporter Type 2 and Its Related Ion Transport System in the Rat Endolymphatic Sac

“…In accordance with a report by Guild (1927), the ES was subdivided into three parts, proximal sac portion (PSP), intermediate sac portion (ISP), and distal sac portion (DSP), and this proposed subdivision is still being followed. Although absolute confirmation has not yet been obtained, ISP may be the most important part of the ES involved in endolymph absorption (Hoshikawa et al 1994;Dahlmann and von During 1995;Miyashita et al 2007).…”