Physiologically silent sodium channels in mammalian outer hair cells

Abstract

1. Voltage-dependent properties of isolated guinea pig outer hair cells (OHCs) were investigated using whole-cell recording. An inward current was detected in approximately 10% of the cells. This inward current was identified as belonging to the voltage-activated sodium current family on the basis of its high sensitivity to tetrodotoxin and the effect of substitution of impermeant ions. Although this is the first report of a sodium current in the mammalian cochlea, it differs from the classical neuronal sodium current by having a variable magnitude from cell to cell and an inactivation that is shifted to hyperpolarized potentials. The sensory processing role of hair cells in general and outer hair cells in particular could be disrupted by the presence of a regenerative voltage-dependent current. The functional role of the OHC sodium channels is puzzling, particularly as they may be silent in vivo.

Ionic currents expressed in a cell line derived from the organ of Corti of the Immortomouse

“…This current is not present in adult guinea-pig inner hair cells but has been observed in possibly younger adult guinea-pig outer hair cells in one study [34]. Similar currents have been seen in hair cells from the embryonic chick otocyst [32] and neonatal mouse utricle [30].…”

Developmental Acquisition of Voltage-Dependent Conductances and Sensory Signaling in Hair Cells of the Embryonic Mouse Inner Ear

“…G Na in embryonic vestibular hair cells is almost completely inactivated at typical resting potentials, suggesting that it is physiologically silent, similar to the sodium conductance in outer hair cells (Witt et al, 1994). However, we cannot exclude the possibility that the in vivo properties differ from those we described in vitro.…”

“…Transient expression of sodium currents has been documented in auditory hair cells (Evans and Fuchs, 1987;Witt et al, 1994;Oliver et al, 1997;Marcotti et al, 2003) but has not been widely reported in vestibular cells (Masetto et al, 2003). One preliminary report suggested the presence of TTX-resistant sodium currents in mammalian vestibular hair cells (Rüsch and Eatock, 1997).…”

Development of K+ and Na+ conductances in rodent postnatal semicircular canal type I hair cells

“…We found a rapidly activating, rapidly inactivating inward Na ϩ current in postnatal SCC rat and gerbil hair cells. A transient sodium current, I Na , has been described previously in hair cells from mouse and rat utricle (2,14,19,35), mouse, rat and guinea pig cochlea (20,24,34) and chicken vestibular system (23,33). In mouse utricle I Na peaked at E16 -E18 and subsequently declined to almost zero at birth (14).…”