title: Endocytosis of microperoxidase in the marginal cells of stria vascularis.
abstract: OBJECTIVE
  Endocytosis has been thought to control entry into the cell and play a crucial role in the development, immune response, neurotransmission, intercellular communication, signal transduction, and cellular and organismal homeostasis. We investigated the basic properties of endocytosis in the marginal cells of stria vascularis (SV) to discuss whether marginal cells have a potential to maintain the endolymph homeostasis.
  
  
  METHODS
  We perfused microperoxidase (MPO), an endocytosis tracer, into the cochlear duct. After 5-60 min of endolymphatic perfusion, the tissues were fixed and the distribution of MPO within the marginal cell was observed by transmission electron microscopy.
  
  
  RESULTS
  Endocytosis started already at 5 min after MPO perfusion. Small MPO-loaded endosomes were observed up to 30 min after MPO perfusion. The small tubulovesicular endosomes and the plasma membrane invagination were not decorated by an electron dense bristle structure. After endocytosis, MPO labeled preendosomes were quickly transported to the large vacuolar endosomes that connected with tubular endosomes. At 60 min after MPO perfusion, MPO-loaded large vesicles that have small vesicles in the lumen were observed.
  
  
  CONCLUSIONS
  The time-course of MPO-loaded endosomes was similar to that of CF-loaded endosomes in the marginal cells of SV. The strial marginal cells have vigorous endocytotic activity both in clathrin-independent and clathrin-dependent endocytosis. This high activity of endocytosis in SV seems to be needed to maintain the homeostasis of endolymph via membranous channels and/or receptors regulations.
authors.affiliation: Department of Otolaryngology, Kochi Medical School, Nankoku, Kochi 783-8505, Japan. kakigia@med.kochi-u.ac.jp
authors.forename: Akinobu
authors.initials: A
authors.lastname: Kakigi
authors.forename: Teruhiko
authors.initials: T
authors.lastname: Okada
authors.forename: Taizo
authors.initials: T
authors.lastname: Takeda
authors.forename: Daizo
authors.initials: D
authors.lastname: Taguchi
authors.forename: Rie
authors.initials: R
authors.lastname: Nishioka
mesh_terms: D000818:Animals; D003051:Cochlea / Q000187:drug effects / Q000648:ultrastructure; D004705:Endocytosis / Q000187:drug effects*; D004710:Endolymph / Q000502:physiology; D006168:Guinea Pigs; D006706:Homeostasis / Q000502:physiology; D046529:Microscopy, Electron, Transmission; D010544:Peroxidases / Q000008:administration & dosage / Q000493:pharmacokinetics*; D013316:Stria Vascularis / Q000166:cytology* / Q000201:enzymology*
chemical_list: D010544:Peroxidases; C021799:microperoxidase