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Voltage-Gated Outward K Currents in Frog Saccular Hair Cells

Dipartimento di Biologia Cellulare e Molecolare, Università di Perugia, I-06123 Perugia, Italy

Submitted 28 March 2003; accepted in final form 4 September 2003

A biophysical analysis of the voltage-gated K (K_v) currents of frog saccular hair cells enzymatically isolated with bacterial protease VIII was carried out, and their contribution to the cell electrical response was addressed by a modeling approach. Based on steady-state and kinetic properties of inactivation, two distinct K_v currents were found: a fast inactivating I_A and a delayed rectifier I_DRK. I_A exhibited a strongly hyperpolarized inactivation V_1/2 (-83 mV), a relatively rapid single exponential recovery from inactivation (_rec of 100 ms at -100 mV), and fast activation and deactivation kinetics. I_DRK showed instead a less-hyperpolarized inactivation V_1/2 (-48 mV), a slower, double-exponential recovery from inactivation (_rec1 490 ms and _rec2 4,960 ms at -100 mV), and slower activation and deactivation kinetics. Steady-state activation gave a V_1/2 and a k of -46.2 and 8.2 mV for I_A and -48.3 and 4.2 mV for I_DRK. Both currents were not appreciably blocked by bath application of 10 mM TEA, but were inhibited by 4-AP, with I_DRK displaying a higher sensitivity. I_DRK also showed a relatively low affinity to linopirdine, being half blocked at 50 µM. Steady-state and kinetic properties of I_DRK and I_A were described by 2nd- and 3rd-order Hodgkin–Huxley models, respectively. The goodness of our quantitative description of the K_v currents was validated by including I_A and I_DRK in a theoretical model of saccular hair cell electrical activity and by comparing the simulated responses with those obtained experimentally. This thorough description of the I_DRK and I_A will contribute toward understanding the role of these currents in the electrical response on this preparation.

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