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Quantification of solute entry into cochlear perilymph through the round window membrane.
1Department of Otolaryngology, Washington University School of Medicine, St. Louis, MO 63110, USA. salta@msnotes.wustl.edu
Hearing Research
|June 26, 2001
Summary
Drug delivery to the inner ear via the round window membrane is common, but drug levels are unknown. This study used simulations and marker ions in guinea pigs to map drug distribution in cochlear fluids.
Area of Science:
- Otoacoustic emissions and inner ear drug delivery research.
- Computational modeling of physiological processes.
- Pharmacokinetics and drug distribution studies.
Background:
- Drug administration to the inner ear through the round window membrane is increasingly utilized.
- Understanding drug distribution within cochlear fluid spaces is crucial for optimizing therapeutic outcomes.
- Previous studies have not precisely quantified drug concentrations in different cochlear regions following round window administration.
Purpose of the Study:
- To simulate and experimentally determine the distribution of a marker solute within the cochlear fluid spaces after round window membrane administration.
- To establish the actual drug levels achieved in various cochlear regions using this delivery method.
- To provide a foundational understanding of solute distribution dynamics in the cochlea for future drug delivery applications.
Main Methods:
- Utilized simulations of solute movement in cochlear fluids, validated with experimental measurements.
- Employed trimethylphenylammonium (TMPA) as a marker ion and TMPA-selective microelectrodes to monitor concentrations in scala tympani (ST).
- Applied TMPA to perilymph via round window membrane irrigation and analyzed distribution using the Washington University Cochlear Fluids Simulator.
Main Results:
- Measured TMPA concentrations of 330 microM in the first turn (1.4 mm from base) and 15 microM in the second turn (7.5 mm from base) after 90 minutes.
- Simulation parameters indicated round window permeability of 1.9 x 10(-8) cm/s, ST clearance half-time of 60 min, and longitudinal perilymph flow of 4.4 nl/min.
- Solute distribution in apical regions is mainly governed by diffusion and clearance rates; longitudinal flow is significant only with otic capsule perforation.
Conclusions:
- Demonstrated that solute distribution in apical cochlear regions is primarily diffusion- and clearance-dependent.
- Found that longitudinal perilymph flow has a minimal impact on solute distribution unless the otic capsule is compromised.
- Provided a framework for predicting the distribution of other substances administered via the round window membrane.