M-like K+ currents in type I hair cells and calyx afferent endings of the developing rat utricle.
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.
Hurley
Karen M
KM
The Bobby R. Alford Department of Otorhinolaryngology, Head and Neck Surgery, Baylor College of Medicine, Houston, Texas 77030, USA.
Gaboyard
Sophie
S
Zhong
Meng
M
Price
Steven D
SD
Wooltorton
Julian R A
JR
Lysakowski
Anna
A
Eatock
Ruth Anne
RA
D000818:Animals; D000831:Animals, Newborn; D018069:Hair Cells, Vestibular / Q000187:drug effects / Q000254:growth & development*; D066298:In Vitro Techniques; D051656:KCNQ Potassium Channels / Q000037:antagonists & inhibitors / Q000502:physiology; D009411:Nerve Endings / Q000187:drug effects / Q000502:physiology*; D009475:Neurons, Afferent / Q000187:drug effects / Q000502:physiology*; D026902:Potassium Channel Blockers / Q000494:pharmacology; D015221:Potassium Channels / Q000502:physiology*; D051381:Rats; D020318:Rats, Long-Evans; D012444:Saccule and Utricle / Q000187:drug effects / Q000254:growth & development*
D051656:KCNQ Potassium Channels; D026902:Potassium Channel Blockers; D015221:Potassium Channels