The Membrane Properties of Cochlear Root Cells are Consistent with Roles in Potassium Recirculation and Spatial Buffering.
Auditory transduction, amplification, and hair cell survival depend on the regulation of extracellular [K(+)] in the cochlea. K(+) is removed from the vicinity of sensory hair cells by epithelial cells, and may be distributed through the epithelial cell syncytium, reminiscent of "spatial buffering" in glia. Hypothetically, K(+) is then transferred from the epithelial syncytium into the connective tissue syncytium within the cochlear lateral wall, enabling recirculation of K(+) back into endolymph. This may involve secretion of K(+) from epithelial root cells, and its re-uptake via transporters into spiral ligament fibrocytes. The molecular basis of this secretion is not known. Using a combination of approaches we demonstrated that the resting conductance in guinea pig root cells was dominated by K(+) channels, most likely composed of the Kir4.1 subunit. Dye injections revealed extensive intercellular gap junctional coupling, and delineated the root cell processes that penetrated the spiral ligament. Following uncoupling using 1-octanol, individual cells had Ba(2+)-sensitive weakly rectifying currents. In the basal (high-frequency encoding) cochlear region K(+) loads are predicted to be the highest, and root cells in this region had the largest surface area and the highest current density, consistent with their role in K(+) secretion. Kir4.1 was localized within root cells by immunofluorescence, and specifically to root cell process membranes by immunogold labeling. These results support a role for root cells in cochlear K(+) regulation, and suggest that channels composed of Kir4.1 subunits may mediate K(+) secretion from the epithelial gap junction network.
Jagger
Daniel J
DJ
Centre for Auditory Research, UCL Ear Institute, University College London, 332 Gray's Inn Road, London, WC1X 8EE UK.
Nevill
Graham
G
Centre for Auditory Research, UCL Ear Institute, University College London, 332 Gray's Inn Road, London, WC1X 8EE UK.
Forge
Andrew
A
Centre for Auditory Research, UCL Ear Institute, University College London, 332 Gray's Inn Road, London, WC1X 8EE UK.
D000818:Animals; D001464:Barium / Q000494:pharmacology; D003051:Cochlea / Q000166:cytology* / Q000502:physiology*; D017629:Gap Junctions / Q000502:physiology; D006168:Guinea Pigs; D011188:Potassium / Q000378:metabolism*; D024661:Potassium Channels, Inwardly Rectifying / Q000502:physiology*; D000098854:Kcnj10 Channel
D000098854:Kcnj10 Channel; D024661:Potassium Channels, Inwardly Rectifying; D001464:Barium; D011188:Potassium
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