Ionic and potential changes of the endolymphatic sac induced by endolymph volume changes.

Area of Science:

• Otolaryngology
• Inner Ear Physiology
• Fluid Balance

Background:

• The endolymphatic sac (ES) is implicated in regulating inner ear fluid volume.
• Previous research indicates anatomical changes in the ES correlating with endolymph volume fluctuations.
• This suggests the ES's function is dynamic and responsive to endolymph status.

Purpose of the Study:

• To investigate the physiological response of the endolymphatic sac (ES) to changes in cochlear endolymph volume.
• To measure luminal concentrations of potassium (K+) and sodium (Na+) within the ES.
• To assess the endolymphatic sac potential (ESP) during induced endolymph volume alterations.

Main Methods:

• Recordings of luminal K+ and Na+ concentrations were performed from the ES via an extradural approach.
• Cochlear endolymph volume changes were induced by injecting or withdrawing fluid through the round window.
• Endolymphatic sac potential (ESP) was monitored concurrently.

Main Results:

• Endolymphatic injections led to a sustained increase in ES K+ (average 19.9 mM) and a decrease in Na+ (average 30.7 mM).
• The rate of K+ increase correlated with injected fluid volume.
• Endolymphatic withdrawals caused a slow decrease in ES K+ (average 3.4 mM) without significant Na+ change.
• Volume-induced ESP changes were variable and not statistically significant.

Conclusions:

• Changes in cochlear endolymph volume trigger a sustained physiological response in the endolymphatic sac.
• The observed prolonged ionic changes suggest a slow process for endolymph volume restoration by the ES.
• The ES actively participates in the inner ear's fluid balance, albeit with a delayed response.