Round window membrane. Structure function and permeability: A review

Abstract

The ultrastructure of the round window membrane of humans, monkeys, felines, and rodents discloses three basic layers: an outer epithelium, a middle core of connective tissue, and an inner epithelium. Interspecies variations are mainly in terms of thickness, being thinnest in rodents and thicker in humans. Morphologic evidence suggests that the layers of the round window participate in absorption and secretion of substances to and from the inner ear, and that the entire membrane could play a role in the defense system of the ear. Different substances, including antibiotics, local anesthetics, and tracers such as cationic ferritin, horseradish peroxidase, and 1 mu latex microspheres, are placed in the middle ear side traverse the membrane. Cationic ferritin and 1 micron microspheres placed in perilymph become incorporated by the inner epithelial cells of the membrane. Permeability is selective; factors include size, concentration, liposolubility, electrical charge, and thickness of the membrane. Passage of substances through the round window membrane is by different pathways, the nature of which is seemingly decided at the outer epithelium of the round window membrane.

Complex modulus of round window membrane over auditory frequencies in normal and otitis media chinchilla ears

“…The role of RWM is to release mechanical energy and/or conduct sound vibration to the scala tympani of the cochlea (Wever and Lawrence, 1948;Goycoolea and Lundman, 1997). The compliance of RWM affects its ability to be displaced by, or to displace, cochlear perilymph.…”

Topical application of the antiapoptotic TAT-FNK protein prevents aminoglycoside-induced ototoxicity

“…20 --22,16 --18 The structure of the outer epithelium is such that substances can pass from the middle to the inner ear by selective absorption and secretion. 23 The factors influencing permeability through the RWM include the molecular weight and configuration of the protein, its contact time and the concentration of the substances in the middle ear.…”

Mathematical modeling for local trans-round window membrane drug transport in the inner ear

“…where, h from Equation (33) is the thickness of RWM, which is approximately 10 mm in the guinea pig (Goycoolea & Lundman, 1997).…”

“…It consists of three basic layers: an outer epithelium layer, a middle core of connective tissue, and an inner epithelium (Hellstrom et al, 1989). Animal studies have shown that this triple-layered membrane absorbs or secretes substances in the inner ear, which makes it the main portal for drug delivery to the inner ear (Juhn et al, 1989;Goycoolea & Lundman, 1997). For further development and translation of this promising therapeutic strategy to controlled clinical trials, it is necessary to conduct preclinical studies to establish pharmacokinetic and toxicological dose-effect relationships.…”