Functional and morphological findings of endolymphatic sac

Area of Science:

• Otolaryngology
• Inner ear physiology
• Fluid dynamics

Background:

• Endolymphatic hydrops is a condition characterized by excess fluid in the inner ear.
• The endolymphatic sac's role in regulating inner ear fluid homeostasis is not fully understood.

Purpose of the Study:

• To investigate the function of the endolymphatic sac in the development of endolymphatic hydrops.
• To explore the potential active transport mechanisms within the endolymphatic sac epithelium.

Main Methods:

• Obliteration of the endolymphatic sac and duct in animal models.
• Measurement of d.c. potential, K+ activity, and protein content in endolymph.
• Intra-endolymphatic sac injection of Thorotrast.
• Administration of ethacrynic acid and subsequent histological analysis (light and electron microscopy).

Main Results:

• No significant changes in d.c. potential, K+ activity, or protein content were observed during endolymphatic hydrops development after sac obliteration.
• K+ activity was significantly lower in the endolymphatic sac compared to the cochlear endolymph.
• Thorotrast particles were detected in cochlear endolymph after injection into the endolymphatic sac.
• Ethacrynic acid decreased cochlear endolymph K+ activity but increased it in the endolymphatic sac, causing intercellular edema in both.

Conclusions:

• The endolymphatic sac exhibits an active transport mechanism.
• This mechanism is involved in regulating endolymph composition and volume.
• Findings suggest a potential role for the endolymphatic sac in the pathophysiology of endolymphatic hydrops.