Voltage-and calcium-activated potassium channels (BK) are important regulators of neuronal excitability. BK channels seem to be crucial for frequency tuning in nonmammalian vestibular and auditory hair cells. However, there are a paucity of data concerning BK expression in mammalian vestibular hair cells. We therefore investigated the localization of BK channels in mammalian vestibular hair cells, specifically in rat vestibular neuroepithelia. We find that only a subset of hair cells in the utricle and the crista ampullaris express BK channels. BK-positive hair cells are located mainly in the medial striolar region of the utricle, where they constitute at most 12% of hair cells, and in the central zone of the horizontal crista. A majority of BK-positive hair cells are encapsulated by a calretinin-positive calyx defining them as type I cells. The remainder are either type I cells encapsulated by a calretinin-negative calyx or type II hair cells. Surprisingly, the number of BK-positive hair cells in the utricle peaks in juvenile rats and declines in early adulthood. BK channels were not found in vestibular afferent dendrites or somata. Our data indicate that BK channel expression in the mammalian vestibular system differs from the expression pattern in the mammalian auditory and the nonmammalian vestibular system. The molecular diversity of vestibular hair cells indicates a functional diversity that has not yet been fully characterized. The predominance of BK-positive hair cells within the medial striola of juvenile animals suggests that they contribute to a scheme of highly lateralized coding of linear head movements during late development.
Indexing termsutricle; crista ampullaris; hair cells; striola; calretinin; immunohistochemistry Large-conductance, voltage-and calcium-activated potassium channels (BK channels, also known as K Ca 1.1, KCNMA1, Slo1 or maxi-K) are important contributors to neuronal excitability by, for example, regulating the duration of calcium action potential trains, shaping the after-hyperpolarization, and curtailing calcium entry at the presynaptic nerve terminal (Salkoff et al., 2006). They are frequently clustered together with calcium channels (Issa and Hudspeth, 1994;Samaranayake et al., 2004), especially at presynaptic terminals, where they might regulate synaptic transmission (Augustine et al., 1988; Robitaille et al., 1993). BK channels contribute to electrical tuning in auditory hair cells of amphibians, reptiles, and birds (Fettiplace and Fuchs, 1999), and variations in expression of BK α-subunit splice variants and β-subunits along the auditory epithelium parallel its tonotopic organization (Ramanathan et al., 1999). Vestibular hair cells of the frog sacculus, which also exhibit electrical tuning and have auditory characteristics in signaling ground vibrations (Smotherman and Narins, 2000), express BK channels that are clustered together with calcium channels at the release sites (Roberts et al., 1990). This arrangement suggests tuning not only of the electrical resonanc...