Na+ currents in vestibular type I and type II hair cells of the embryo and adult chicken.
In birds, type I and type II hair cells differentiate before birth. Here we describe that chick hair cells, from the semicircular canals, begin expressing a voltage-dependent Na current (INa) from embryonic day 14 (E14) and continue to express the current up to hatching (E21). During this period, INa was present in most (31/43) type I hair cells irrespective of their position in the crista, in most type II hair cells located far from the planum semilunatum (48/63), but only occasionally in type II hair cells close to the planum semilunatum (2/35). INa activated close to -60 mV, showed fast time- and voltage-dependent activation and inactivation, and was completely, and reversibly, blocked by submicromolar concentrations of tetrodotoxin (Kd = 17 nM). One peculiar property of INa concerns its steady-state inactivation, which is complete at -60 mV (half-inactivating voltage = -96 mV). INa was found in type I and type II hair cells from the adult chicken as well, where it had similar, although possibly not identical, properties and regional distribution. Current-clamp experiments showed that INa could contribute to the voltage response provided that the cell membrane was depolarized from holding potentials more negative than -80 mV. When recruited, INa produced a significant acceleration of the cell membrane depolarization, which occasionally elicited a large rapid depolarization followed by a rapid repolarization (action-potential-like response). Possible physiological roles for INa in the embryo and adult chicken are discussed.
Masetto
S
S
Dipartimento di Scienze Fisiologiche-Farmacologiche Cellulari-Molecolari-Sez. di Fisiologia Generale e Biofisica Cellulare, Università di Pavia, 27100 Pavia, Italy. smasetto@unipv.it
Bosica
M
M
Correia
M J
MJ
Ottersen
O P
OP
Zucca
G
G
Perin
P
P
Valli
P
P
D000818:Animals; D002642:Chick Embryo; D002645:Chickens; D004594:Electrophysiology; D018069:Hair Cells, Vestibular / Q000196:embryology / Q000254:growth & development* / Q000502:physiology*; D018408:Patch-Clamp Techniques; D012665:Semicircular Canals / Q000254:growth & development / Q000502:physiology; D015222:Sodium Channels / Q000502:physiology*
D015222:Sodium Channels