Localization and developmental expression of BK channels in mammalian cochlear hair cells

Acceleration of Age-Related Hearing Loss by Early Noise Exposure: Evidence of a Misspent Youth

“…The inner ear is mature morphologically, and electrophysiologic properties of hair cells and gross cochlear response thresholds have stabilized by 4 weeks, the youngest animals studied here (Mikaelian et al, 1965;Lim and Anniko, 1985;Marcotti et al, 2003;Hafidi et al, 2005). Thresholds in the 8 -16 kHz range are almost identical in 4-versus 16-week-old animals (Fig.…”

The Role of BKCa Channels in Electrical Signal Encoding in the Mammalian Auditory Periphery

“…Thus, an additional mechanism appears to contribute to the decrease in spike rates. This mechanism may be postsynaptic given that spiral ganglion neurons may contain BK Ca channels (Skinner et al, 2003;Hafidi et al, 2005) and loss of BK Ca channels can decrease neuronal spike rates .…”

“…Because AN tuning was normal in BK␣ Ϫ/Ϫ , we conclude that OHC pathology was not severe in the age range used. Expression of BK Ca channels was reported in cochlear cell types related to the production of endolymph and the endolymphatic potential (EP) (Shen et al, 2004;Hafidi et al, 2005); therefore, the possibility should be considered that EP, driving the transduction current of the IHC, is reduced in BK␣ Ϫ/Ϫ . Our AN data indicate that this is not the case.…”

“…However, IHC depolarization on the order of 10 mV only slightly reduces the driving force for Ca 2ϩ , which may be too small to precipitate a relevant shift of the transfer curve (Assad et al, 1989;Kennedy et al, 2003). Postsynaptic effects of BK Ca deletion must also be considered given reports of BK Ca expression in the somata of AN fibers (Skinner et al, 2003;Hafidi et al, 2005) and pharmacological evidence for BK Ca in developing AN neurons (Adamson et al, 2002). Activation of BK Ca during neuronal APs contributes to the afterhyperpolarization, which facilitates repetitive firing by promoting rapid recovery of Na ϩ channels from inactivation (Klyachko et al, 2001).…”

Plasticity in Membrane Cholesterol Contributes toward Electrical Maturation of Hearing

“…The functional expression of low voltage-activated K ϩ currents (I K,n ) derived from K v 7.4 channels and Ca 2ϩ -activated K ϩ currents at later stages of development clamps the membrane potential close to the reversal potential of K ϩ (2,3,9,10). Additionally, a reduction in the Ca 2ϩ current density and the late-stage disappearance of low voltage-activated Ca 2ϩ current (4) both contribute toward the transition from SAPs to graded receptor potentials, yet the underlying mechanisms for the latestage functional appearance of K ϩ currents are unknown, despite evidence to demonstrate that K ϩ channel genes and products are expressed several days prior to hair cell maturation (11,12).…”