Calbindin-D28K localization in the primate inner ear.

The distribution of one of the calcium-binding proteins, calbindin-D28K (CB-D28K), was studied in the adult human and squirrel monkey inner ear by means of immunocytochemical methods. Inner and outer hair cells in the organ of Corti and vestibular hair cells showed CB-D28K immunoreactivity, though some vestibular hair cells were devoid of immunoreactivity. In the spiral and vestibular ganglion, immunoreactive cells were found in both the squirrel monkey and human. The present results indicate that CB-D28K is localized within afferent neuronal components in these sensory organs and may regulate Ca++ levels for optimal neurotransmission in the primate auditory and vestibular systems. This study also provides evidence of two nonneuronal localizations of CB-D28K in the squirrel monkey. Subpopulations of fibrocytes in the spiral ligament and vestibular end organs were enriched with CB-D28K, suggesting that these cells are possibly equipped with the function to regulate Ca++ concentration in the perilymphatic fluid. In the maculae, many CB-D28K-immunoreactive particles were found in the otoconial membrane, indicating that CB-D28K may participate in the formation of otoconia.