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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 and Ruth Anne Eatock^1,2

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 (V_1/2) 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 (V_1/2 of –60 mV) and g_–80 (V_1/2 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

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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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