Channeling your inner ear potassium: K+ channels in vestibular hair cells

During development of vestibular hair cells, K+ conductances are acquired in a specific pattern. Functionally mature vestibular hair cells express different complements of K+ channels which uniquely shape the hair cell receptor potential and filtering properties. In amniote species, type I hair cells (HCI) have a large input conductance due to a ubiquitous low–voltage-activated K+ current that activates with slow sigmoidal kinetics at voltages negative to the membrane resting potential. In contrast type II hair cells (HCII) from mammalian and non-mammalian species have voltage-dependent outward K+ currents that activate rapidly at or above the resting membrane potential and show significant inactivation. A-type, delayed rectifier and calcium-activated K+ channels contribute to the outward K+ conductance and are present in varying proportions in HCII. In many species, K+ currents in HCII in peripheral locations of vestibular epithelia inactivate more than HCII in more central locations. Two types of inward rectifier currents have been described in both HCI and HCII. A rapidly activating K+-selective inward rectifier current (IK1, mediated by Kir2.1 channels) predominates in HCII in peripheral zones, whereas a slower mixed cation inward rectifier current (Ih), shows greater expression in HCII in central zones of vestibular epithelia. The implications for sensory coding of vestibular signals by different types of hair cells are discussed.This article is part of a Special Issue entitled .