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The Journal of Neuroscience, October 4, 2006, 26(40):10253-10269; doi:10.1523/JNEUROSCI.2596-06.2006
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Cellular/Molecular
M-Like K+ Currents in Type I Hair Cells and Calyx Afferent Endings of the Developing Rat Utricle
Karen M. Hurley,1 Sophie Gaboyard,3 Meng Zhong,1 Steven D. Price,3 Julian R. A. Wooltorton,2 Anna Lysakowski,3 andRuth Anne Eatock1,2 1The Bobby R. Alford Department of Otorhinolaryngology, Head and Neck Surgery and 2Department of Neuroscience, Baylor College of Medicine, Houston, Texas 77030, and 3Department of Anatomy and Cell Biology, University of Illinois, Chicago, Illinois 60612
Correspondence should be addressed to: Ruth Anne Eatock, Eaton-Peabody Laboratory, Massachusetts Eye and Ear Infirmary, 243 Charles Street, Boston, MA 02114. Email: eatock{at}meei.harvard.edu
Type I vestibular hair cells have large K+ currents that, like neuronal M currents, activate negative to resting potential and are modulatable. In rodents, these currents are acquired postnatally. In perforated-patch recordings from rat utricular hair cells, immature hair cells [younger than postnatal day 7 (P7)] had a steady-state K+ conductance (g–30) with a half-activation voltage (V1/2) of –30 mV. The size and activation range did not change in maturing type II cells, but, by P16, type I cells had added a K conductance that was on average fourfold larger and activated much more negatively. This conductance may comprise two components: g–60 (V1/2 of –60 mV) and g–80 (V1/2 of –80 mV). g–80 washed out during ruptured patch recordings and was blocked by a protein kinase inhibitor.
M currents can include contributions from KCNQ and ether-a-go-go-related (erg) channels. KCNQ and erg channel blockers both affected the K+ currents of type I cells, with KCNQ blockers being more potent at younger than P7 and erg blockers more potent at older than P16. Single-cell reverse transcription-PCR and immunocytochemistry showed expression of KCNQ and erg subunits. We propose that KCNQ channels contribute to g–30 and g–60 and erg subunits contribute to g–80.
Type I hair cells are contacted by calyceal afferent endings. Recordings from dissociated calyces and afferent endings revealed large K+ conductances, including a KCNQ conductance. Calyx endings were strongly labeled by KCNQ4 and erg1 antisera. Thus, both hair cells and calyx endings have large M-like K+ conductances with the potential to control the gain of transmission.
Key words: vestibular; KCNQ channels; erg channels; development; hair cells; M current
Received June 20, 2006; revised Aug. 18, 2006; accepted Aug. 21, 2006.
Correspondence should be addressed to: Ruth Anne Eatock, Eaton-Peabody Laboratory, Massachusetts Eye and Ear Infirmary, 243 Charles Street, Boston, MA 02114. Email: eatock{at}meei.harvard.edu
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