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

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 (I_TEA) and insensitive to 4-aminopyridine (4-AP), activated at 40 mV and exhibited slow activation (_ac, 38.4 ± 7.8 ms at 30 mV, mean ± SD). I_TEA had a half activation potential [V_ac(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 [V_inac(1/2)] of 62.4 ± 0.2 mV. The second current, sensitive to 4-AP (maximum block around 0.5 mM) and to -dendrotoxin (I_DTX) appeared at 60 mV. Complete block of I_DTX was achieved using either 20 nM -DTX or 50 nM margatoxin. This current activated 10 times faster than I_TEA (_ac, 3.5 ± 0.8 ms at 50 mV) with V_ac(1/2) of 51.2 ± 0.6 mV, and inactivated only slightly compared with I_TEA (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 (I_BDS-I) activated around 60 mV. It displayed fast activation (_ac, 2.3 ± 0.4 ms at 50 mV) and fast and complete voltage-dependent inactivation. I_BDS-I had a V_ac(1/2) of 31.3 ± 0.4 mV and V_inac(1/2) of 65.8 ± 0.3 mV. It displayed faster time-dependent inactivation and recovery from inactivation than I_TEA. The three types of current were found in all the neurons investigated. Although I_TEA was the major current, the proportion of I_DTX and I_BDS-I varied considerably between neurons. The ratio of the density of I_BDS-I to that of I_DTX 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.