The Orientation And Its Significance Of Aquaporin-2 In The Rat Inner Ear

Objective:There is a complicated duct-liquid balance system in the inner ear,which includes the endolymph and the perilymph.The endolymph,sequestered within a closed membranous chamber,the scala media,has high and low concentration of K+ and Na+,respectively.The perilymph,sequestered within membranous chambers,scala tympani and scala vestibuli joined at the apex of the cochlea,has high and low concentration of Na+ and K+,respectively,composition that is similar to the plasma.The distinct composition of these two fluids translates into a positive potential of 80mV between the endolymph and the perilymph.Both the Corti's organ and hair cells in vestibule are exposed to the space filled with endolymph,from which we see the homeostasis of solute concentrations,osmotic /electrical gradients between the fluid filled scalae and total volume of the inner fluids plays an important role in maintaining hearing and balance.The endolymph is manufactured by stria vascularis and reabsorbed by the endolymphatic sac.The Reissner's membrane,Corti's organ and vestibulum's dark cell also take part in the control of endolymph,but the extent to which they contribute is notclear.Dysfunction of endolymph leads to serious pathological and physiological results such as endolymph hydrops.Meniere'disease is a common disease in otorhinolaryngology characteristic of paroxysmal positional vertigo,tinnitus,deafness,and sense of fullness in the ear.Reduced reabsorption of endolymph in the endolymphatic sac of the inner ear is the most favoured hypothesis underlying the pathology of Meniere'disease. Meniere'disease has been correlated to abnormally high plasma levels of antidiuretic hormone vasopressin(AVP/ADH).Water channels,also known as aquaporins(AQPs),are proteins that facilitate rapid and selective transmembrane movement of water down an osmotic gradient.They consist at least 10 subtypes in mammals and distribute widely in the plasma membranes of many tissues.Functionally aquaporins belong to major intrinsic protein family and desfunction of them may potentially cause fluid and electrolyte disturbance in the body resulting in tissue/organ disorder.Until to now,we have found 8 subtypes of AQPs in the mammal inner ear,AQP-1,2,3,4,5,6,7,9.Among them AQP-2 is the only ADH/AVP regulated water channel.It mainly expresses in the renal collecting duct,thus contributes to urine concentration.It is thought that the inner ear shares structural and anatomic similarities with the kidney and that the two organs may utilize the similar physiological mechanisms of electrolyteregulation because certain drugs such as aminoglycoside antibiotics and nonsteroidal anti-inflammatory drugs,are both ototoxic and nephrotoxic. In this study we planned to examine the expression of AQP-2 in the normal rats'ear as well as endolymph hydrops model rats'ear,and then insquire into its role in the inner ear water metablism.Thus we may provide basis for the prevention and treatment of Meniere'disease.However,because of funds and technique,we failed to set up the endolymph hydrops model.In view of the common character of AQPs,we additionally studied AQP-2 distribution in different type and phase nasal polyps and the effects of intranasal Fluticasone propionate(FP) on the expression of AQP-2 in nasal polyps.We found that AQP-2 contributed to the edema of nasal polyps and FP may lesson edema through changing the expression of AQP-2.Please see partâ…¡ of the paper.As such study is at the beginning stage,we can't give a summarization here at present. Methods:Streptavidinperoxidase immunohistochemical technique was used in this study.1 Tissue processingFifteen normal adult male rats were used( 300~350g body weigh) in this study.The animals were anaesthetized with an injection of urethane(1.5g/Kg) and the left ventricle was perfused through thoracotomy with saline followed by 4% paraformaldehyde in PBS until the tails and napes of the rats turned stiff.The kidneys were harvested immediately.Thetemporal bon...