The distribution of one of the calcium-binding proteins, calbindin-D28
K (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 immuno
reactivity, though some vestibular hair cells were devoid of immunorea
ctivity. In the spiral and vestibular ganglion, immunoreactive cells w
ere found in both the squirrel monkey and human. The present results i
ndicate that CB-D28K is localized within afferent neuronal components
in these sensory organs and may regulate Ca++ levels for optimal neuro
transmission in the primate auditory and vestibular systems. This stud
y also provides evidence of two nonneuronal localizations of CB-D28K i
n the squirrel monkey. Subpopulations of fibrocytes in the spiral liga
ment and vestibular end organs were enriched with CB-D28K, suggesting
that these cells are possibly equipped with the function to regulate C
a++ concentration in the perilymphatic fluid. In the maculae, many CB-
D28K-immunoreactive particles were found in the otoconial membrane, in
dicating that CB-D28K may participate in the formation of otoconia.