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Kinetic Analyses of Three Distinct Potassium Conductances in Ventral Cochlear Nucleus Neurons

The Center for Hearing Science,¹ Department of Biomedical Engineering, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205; and ²Department of Otolaryngology/Head and Neck Surgery, The University of North Carolina, Chapel Hill, North Carolina 27599

Neurons in the ventral cochlear nucleus (VCN) express three distinct K⁺ currents that differ in their voltage and time dependence, and in their inactivation behavior. In the present study, we quantitatively analyze the voltage-dependent kinetics of these three currents to gain further insight into how they regulate the discharge patterns of VCN neurons and to provide supporting data for the identification of their channel components. We find the transient A-type K⁺ current (I_A) exhibits fourth-order activation kinetics (a⁴), and inactivates with one or two time constants. A second inactivation rate (leading to an a⁴bc kinetic description) is required to explain its recovery from inactivation. The dendrotoxin-sensitive low-threshold K⁺ current (I_LT) also activates with fourth-order kinetics (w⁴) but shows slower, incomplete inactivation. The high-threshold K⁺ current (I_HT) appears to consist of two kinetically distinct components (n² + p). The first component activates 10 mV positive to the second and has second-order kinetics. The second component activates with first-order kinetics. These two components also contribute to two kinetically distinct currents upon deactivation. The kinetic behavior of I_HT was indistinguishable amongst cell types, suggesting the current is mediated by the same K⁺ channels amongst VCN neurons. Together these results provide a basis for more realistic modeling of VCN neurons, and provide clues regarding the molecular basis of the three K⁺ currents.

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