title: Evidence for water-permeable channels in auditory hair cells in the leopard frog.
abstract: Auditory hair cells in the amphibian papilla (APHCs) of the leopard frog, Rana pipiens pipiens, have a significantly higher permeability to water than that observed in mammalian hair cells. The insensitivity of water permeability in frog hair cells to extracellular mercury suggests that an amphibian homologue of the water channel aquaporin-4 (AQP4) may mediate water transport in these cells. Using immunocytochemistry, we show that an AQP4-like protein is found in APHCs. Rabbit anti-AQP4 antibody was used in multiple-immunohistochemical staining experiments along with AP hair cell and hair bundle markers in leopard frog and mouse tissue. AQP4 immunoreactivity was found in the basal and apical poles of the APHCs and shows uniform immunoreactivity. This study provides the first identification and localization of an AQP4-like protein in the amphibian inner ear. We also report a more direct measure of hyperosmotically-induced volume changes in APHCs that confirms previous findings. The presence of water channels in anuran APHCs constitutes a novel physiological difference between amphibian and mammalian hair cell structure and function.
authors.affiliation: Department of Head and Neck Surgery, David Geffen School of Medicine, University of California, Los Angeles, CA 90995-1624, USA.
authors.forename: Mia E
authors.initials: ME
authors.lastname: Miller
authors.forename: Arian K
authors.initials: AK
authors.lastname: Nasiri
authors.forename: Peyman O
authors.initials: PO
authors.lastname: Farhangi
authors.forename: Nasser A
authors.initials: NA
authors.lastname: Farahbakhsh
authors.forename: Ivan A
authors.initials: IA
authors.lastname: Lopez
authors.forename: Peter M
authors.initials: PM
authors.lastname: Narins
authors.forename: Dwayne D
authors.initials: DD
authors.lastname: Simmons
mesh_terms: D029845:Amphibian Proteins / Q000378:metabolism*; D000818:Animals; D051401:Aquaporin 4 / Q000378:metabolism; D020346:Aquaporins / Q000378:metabolism*; D002463:Cell Membrane Permeability; D048429:Cell Size; D006198:Hair Cells, Auditory / Q000378:metabolism*; D007150:Immunohistochemistry; D051379:Mice; D008810:Mice, Inbred C57BL; D018613:Microscopy, Confocal; D009995:Osmosis; D011894:Rana pipiens / Q000378:metabolism*; D013997:Time Factors; D014867:Water / Q000378:metabolism*
chemical_list: D029845:Amphibian Proteins; C496031:Aqp4 protein, mouse; D051401:Aquaporin 4; D020346:Aquaporins; D014867:Water