Na+ Currents in Vestibular Type I and Type II Hair Cells of the Embryo and Adult Chicken

• Published in: Journal of neurophysiology Vol. 90; no. 2; pp. 1266 - 1278
• Main Authors: Masetto, S, Bosica, M, Correia, M. J, Ottersen, O. P, Zucca, G, Perin, P, Valli, P
• Format: Journal Article
• Language: English
• Published: United States Am Phys Soc 01.08.2003
• Subjects: Animals; Chick Embryo; Chickens; Electrophysiology; Hair Cells, Vestibular - embryology; Hair Cells, Vestibular - growth & development; Hair Cells, Vestibular - physiology; Patch-Clamp Techniques; Semicircular Canals - growth & development; Semicircular Canals - physiology; Sodium Channels - physiology; Space life sciences
• ISSN: 0022-3077; 1522-1598
• DOI: 10.1152/jn.01157.2002

1 Dipartimento di Scienze Fisiologiche-Farmacologiche Cellulari-Molecolari—Sez. di Fisiologia Generale e Biofisica Cellulare, Università di Pavia, 27100 Pavia, Italy 2 Departments of Otolaryngology, Physiology and Biophysics, and Anatomy and Neurosciences, The University of Texas Medical Branch, Galveston, Texas 77555 3 Centre for Molecular Biology and Neuroscience and Department of Anatomy, Institute of Basic Medical Sciences, University of Oslo, N-0317 Oslo, Norway Submitted 23 December 2002; accepted in final form 4 April 2003 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 ( I Na ) from embryonic day 14 (E14) and continue to express the current up to hatching (E21). During this period, I Na 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). I Na 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 ( K d = 17 nM). One peculiar property of I Na concerns its steady-state inactivation, which is complete at –60 mV (half-inactivating voltage = –96 mV). I Na 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 I Na could contribute to the voltage response provided that the cell membrane was depolarized from holding potentials more negative than –80 mV. When recruited, I Na 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 I Na in the embryo and adult chicken are discussed. Address for reprint requests: Correspondence to: S. Masetto, Dipartimento di Scienze Fisiologiche-Farmacologiche Cellulari-Molecolari – Sez. di Fisiologia Generale e Biofisica Cellulare, Via Forlanini 6, 27100 Pavia, Italy. (E-mail: smasetto{at}unipv.it ).