Voltage-gated calcium channel currents in type I and type II hair cells isolated from the rat crista.
When studied in vitro, type I hair cells in amniote vestibular organs have a large, negatively activating K+ conductance. In type II hair cells, as in nonvestibular hair cells, outwardly rectifying K+ conductances are smaller and more positively activating. As a result, type I cells have more negative resting potentials and smaller input resistances than do type II cells; large inward currents fail to depolarize type I cells above -60 mV. In nonvestibular hair cells, afferent transmission is mediated by voltage-gated Ca2+ channels that activate positive to -60 mV. We investigated whether Ca2+ channels in type I cells activate more negatively so that quantal transmission can occur near the reported resting potentials. We used the perforated patch method to record Ca2+ channel currents from type I and type II hair cells isolated from the rat anterior crista (postnatal days 4-20). The activation range of the Ca2+ currents of type I hair cells differed only slightly from that of type II cells or nonvestibular hair cells. In 5 mM external Ca2+, currents in type I and type II cells were half-maximal at -41.1 +/- 0.5 (SE) mV (n = 10) and -37.2 +/- 0.2 mV (n = 10), respectively. In physiological external Ca2+ (1.3 mM), currents in type I cells were half-maximal at -46 +/- 1 mV (n = 8) and just 1% of maximal at -72 mV. These results lend credence to suggestions that type I cells have more positive resting potentials in vivo, possibly through K+ accumulation in the synaptic cleft or inhibition of the large K+ conductance. Ca2+ channel kinetics were also unremarkable; in both type I and type II cells, the currents activated and deactivated rapidly and inactivated only slowly and modestly even at large depolarizations. The Ca2+ current included an L-type component with relatively low sensitivity to dihydropyridine antagonists, consistent with the alpha subunit being CaV1.3 (alpha1D). Rat vestibular epithelia and ganglia were probed for L-type alpha-subunit expression with the reverse transcription-polymerase chain reaction. The epithelia expressed CaV1.3 and the ganglia expressed CaV1.2 (alpha1C).
Bao
Hong
H
The Bobby R. Alford Department of Otorhinolaryngology and Communicative Sciences, Baylor College of Medicine, Houston, Texas 77030, USA.
Wong
Weng Hoe
WH
Goldberg
Jay M
JM
Eatock
Ruth Anne
RA
D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000502:physiology*; D020746:Calcium Channels, L-Type / Q000502:physiology; D004095:Dihydropyridines / Q000494:pharmacology; D018069:Hair Cells, Vestibular / Q000502:physiology*; D008564:Membrane Potentials; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000502:physiology; D051381:Rats; D020318:Rats, Long-Evans; D020133:Reverse Transcriptase Polymerase Chain Reaction; D009435:Synaptic Transmission; D014722:Vestibule, Labyrinth / Q000502:physiology*
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D004095:Dihydropyridines; D015221:Potassium Channels