Voltage-Gated Outward K Currents in Frog Saccular Hair Cells

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Abstract
A biophysical analysis of the voltage-gated K (Kv) 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 Kvcurrents were found: a fast inactivating IAand a delayed rectifier IDRK. IAexhibited a strongly hyperpolarized inactivation V1/2(-83 mV), a relatively rapid single exponential recovery from inactivation (τrecof ∼100 ms at -100 mV), and fast activation and deactivation kinetics. IDRKshowed instead a less-hyperpolarized inactivation V1/2(-48 mV), a slower, double-exponential recovery from inactivation (τrec1∼ 490 ms and τrec2∼ 4,960 ms at -100 mV), and slower activation and deactivation kinetics. Steady-state activation gave a V1/2and a k of -46.2 and 8.2 mV for IAand -48.3 and 4.2 mV for IDRK. Both currents were not appreciably blocked by bath application of 10 mM TEA, but were inhibited by 4-AP, with IDRKdisplaying a higher sensitivity. IDRKalso showed a relatively low affinity to linopirdine, being half blocked at ∼50 μM. Steady-state and kinetic properties of IDRKand IAwere described by 2nd- and 3rd-order Hodgkin–Huxley models, respectively. The goodness of our quantitative description of the Kvcurrents was validated by including IAand IDRKin a theoretical model of saccular hair cell electrical activity and by comparing the simulated responses with those obtained experimentally. This thorough description of the IDRKand IAwill contribute toward understanding the role of these currents in the electrical response on this preparation.