Korean J Otorhinolaryngol-Head Neck Surg.  2009 Jul;52(7):572-578. 10.3342/kjorl-hns.2009.52.7.572.

Expression of Aquaporin-2 in the Inner Ear of Water-Deprived Guinea Pigs

• Lee SS
• Kim K
• Kim JH
• Cho HH
• Jang CH
• Cho YB

• KMID: 2074135
• DOI: http://doi.org/10.3342/kjorl-hns.2009.52.7.572

Abstract

BACKGROUND AND OBJECTIVES: Although the role of aquaporin-2 (AQP2) in the kidney has been well defined, its role in the inner ear remains to be determined. The present study was to investigate the effect of water deprivation on the expression of AQP2 in the inner ear. MATERIALS AND METHOD: Healthy male guinea pigs weighing 250 g were used. The experimental group underwent water restriction and the control underwent water loading with sucrose-containing water for 3 days. Concentrations of plasma arginine-vasopressin (AVP) were determined and electrocochleography (ECoG) recordings were made. An RT-PCR, real-time PCR and Westernblotting analysis were used for quantitative analysis of AQP2 mRNA and AQP2 protein expression. Immunohistochemistry was also used to evaluate the distribution of AQP2 water channel proteins in the inner ear.
RESULTS
AQP2 was mainly expressed in the epithelium of endolymphatic sac, spiral limbus, spiral ligament and stria vascularis of scala media. The concentrations of plasma AVP were 9.2+/- 0.8 pg/mL in the experimental group and 0.78+/-0.3 pg/mL in the control. The summation potential/ action potential (SP/AP) ratio in ECoG was markedly increased in the experimental group (0.55 in the experimental and 0.29 in the control). RT-PCR and real time PCR as well as Western blot analysis showed that the level of AQP2 mRNA and protein in the cochlea and endolymphactic sac of the water-deprived group was significantly higher than those in the control group.
CONCLUSION
These data suggest that AQP2 is one of the important water channels in fluid homeostasis in the inner ear. Moreover, the volume of endolymphatic space can be increased via AVP-AQP2 system in response to water deprivation.

Keyword

Aquaporin 2; Endolymphatic hydrops; Arginine vasopressin; Inner ear

MeSH Terms

Action Potentials
Animals
Aquaporin 2
Aquaporins
Arginine Vasopressin
Audiometry, Evoked Response
Blotting, Western
Cochlea
Cochlear Duct
Ear, Inner
Endolymphatic Hydrops
Endolymphatic Sac
Epithelium
Guinea
Guinea Pigs
Homeostasis
Humans
Immunohistochemistry
Kidney
Male
Plasma
Real-Time Polymerase Chain Reaction
RNA, Messenger
Spiral Ligament of Cochlea
Stria Vascularis
Water Deprivation
Aquaporin 2
Aquaporins
Arginine Vasopressin
RNA, Messenger