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J Neurophysiol 85: 1017-1026, 2001;
0022-3077/01 $5.00
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The Journal of Neurophysiology Vol. 85 No. 3 March 2001, pp. 1017-1026
Copyright ©2001 by the American Physiological Society

Three Types of Depolarization-Activated Potassium Currents in Acutely Isolated Mouse Vestibular Neurons

C. Chabbert,* J. M. Chambard,* A. Sans, and G. Desmadryl

Institut National de la Santé et de la Recherche Médicale U432, Neurobiologie et Développement du Système Vestibulaire, 34095 Montpellier cedex 5, France

Chabbert, C., J. M. Chambard, A. Sans, and G. Desmadryl. Three Types of Depolarization-Activated Potassium Currents in Acutely Isolated Mouse Vestibular Neurons. J. Neurophysiol. 85: 1017-1026, 2001. The nature and electrophysiological properties of Ca2+-independent depolarization-activated potassium currents were investigated in vestibular primary neurons acutely isolated from postnatal mice using the whole cell configuration of the patch-clamp technique. Three types of currents were identified. The first current, sensitive to TEA (ITEA) and insensitive to 4-aminopyridine (4-AP), activated at -40 mV and exhibited slow activation (tau ac, 38.4 ± 7.8 ms at -30 mV, mean ± SD). ITEA had a half activation potential [Vac(1/2)] of -14.5 ± 2.6 mV and was inactivated by up to 84.5 ± 5.7% by 10-s conditioning prepulses with a half inactivation potential [Vinac(1/2)] of -62.4 ± 0.2 mV. The second current, sensitive to 4-AP (maximum block around 0.5 mM) and to alpha -dendrotoxin (IDTX) appeared at -60 mV. Complete block of IDTX was achieved using either 20 nM alpha -DTX or 50 nM margatoxin. This current activated 10 times faster than ITEA (tau ac, 3.5 ± 0.8 ms at -50 mV) with Vac(1/2) of -51.2 ± 0.6 mV, and inactivated only slightly compared with ITEA (maximum inactivation, 19.7 ± 3.2%). The third current, also sensitive to 4-AP (maximum block at 2 mM), was selectively blocked by application of blood depressing substance (BDS-I; maximum block at 250 nM). The BDS-I-sensitive current (IBDS-I) activated around -60 mV. It displayed fast activation (tau ac, 2.3 ± 0.4 ms at -50 mV) and fast and complete voltage-dependent inactivation. IBDS-I had a Vac(1/2) of -31.3 ± 0.4 mV and Vinac(1/2) of -65.8 ± 0.3 mV. It displayed faster time-dependent inactivation and recovery from inactivation than ITEA. The three types of current were found in all the neurons investigated. Although ITEA was the major current, the proportion of IDTX and IBDS-I varied considerably between neurons. The ratio of the density of IBDS-I to that of IDTX ranged from 0.02 to 2.90 without correlation with the cell capacitances. In conclusion, vestibular primary neurons differ by the proportion rather than the type of the depolarization-activated potassium currents they express.

* C. Chabbert and J. M. Chambard contributed equally to this project.




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