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Abstract:
Human otoconia provide mechanical stimuli to deflect hair cells of the
vestibular sensory epithelium for purposes of detecting linear
acceleration and head tilts. During lifetime, the volume and number of
otoconia are gradually reduced. In a process of degeneration
morphological changes occur. Structural changes in human otoconia are
assumed to cause vertigo and balance disorders such as benign paroxysmal
positional vertigo (BPPV). The aim of this study was to investigate the
main principles of morphological changes in human otoconia in
dissolution experiments by exposure to hydrochloric acid, EDTA,
demineralized water and completely purified water respectively. For
comparison reasons artificial (biomimetic) otoconia (calcite gelatin
nanocomposits) and natural calcite were used. Morphological changes were
detected in time steps by the use of environmental scanning electron
microscopy (ESEM). Under in vitro conditions three main dissolution
mechanisms were identified as causing characteristic morphological
changes of the specimen under consideration: pH drops in the acidic
range, complex formation with calcium ions and changes of ion
concentrations in the vicinity of otoconia. Shifts in pH cause a more
uniform reduction of otoconia size (isotropic dissolution) whereas
complexation reactions and changes of the ionic concentrations within
the surrounding medium bring about preferred attacks at specific areas
(anisotropic dissolution) of human and artificial otoconia. Owing to
successive reduction of material, all the dissolution mechanisms finally
produce fragments and remnants of otoconia. It can be assumed that the
organic component of otoconia is not significantly attacked under the
given conditions. Artificial otoconia serve as a suitable model system
mimicking chemical attacks on biogenic specimens. The underlying
principles of calcite dissolution under in vitro conditions may play a
role in otoconia degeneration processes such as BPPV.
