The Journal of Neurophysiology Vol. 78 No. 5 November 1997, pp. 2235-2245
Copyright ©1997 The American Physiological Society

Hyperpolarization-Activated Inward Current in Neurons of the Rat's Dorsal Nucleus of the Lateral Lemniscus In Vitro

Xiao Wen Fu, Borys L. Brezden, and Shu Hui Wu

Laboratory of Sensory Neuroscience, Institute of Neuroscience, Carleton University, Ottawa, Ontario K1S 5B6, Canada

Fu, Xiao Wen, Borys L. Brezden, and Shu Hui Wu. Hyperpolarization-activated inward current in neurons of the rat's dorsal nucleus of the lateral lemniscus in vitro. J. Neurophysiol. 78: 2235-2245, 1997. The hyperpolarization-activated current (I_h) underlying inward rectification in neurons of the rat's dorsal nucleus of the lateral lemniscus (DNLL) was investigated using whole cell patch-clamp techniques. Patch recordings were made from DNLL neurons of young rats (21-30 days old) in 400 µm tissue slices. Under current clamp, injection of negative current produced a graded hyperpolarization of the cell membrane, often with a gradual sag in the membrane potential toward the resting value. The rate and magnitude of the sag depended on the amount of hyperpolarizing current. Larger current resulted in a larger and faster decay of the voltage. Under voltage clamp, hyperpolarizing voltage steps elicited a slowly activating inward current that was presumably responsible for the sag observed in the voltage response to a steady hyperpolarizing current recorded under current clamp. Activation of the inward current (I_h) was voltage and time dependent. The current just was seen at a membrane potential of 70 mV and was activated fully at 140 mV. The voltage value of half-maximal activation of I_h was 78.0 ± 6.0 (SE) mV. The rate of I_h activation was best approximated by a single exponential function with a time constant that was voltage dependent, ranging from 276 ± 27 ms at 100 mV to 186 ± 11 ms at 140 mV. Reversal potential (E_h) of I_h current was more positive than the resting potential. Raising the extracellular potassium concentration shifted E_h to a more depolarized value, whereas lowering the extracellular sodium concentration shifted E_h in a more negative direction. I_h was sensitive to extracellular cesium but relatively insensitive to extracellular barium. The current amplitude near maximal-activation (about 140 mV) was reduced to 40% of control by 1 mM cesium but was reduced to only 71% of control by 2 mM barium. When the membrane potential was near the resting potential (about 60 mV), cesium had no effect on the membrane potential, current-evoked firing rate and input resistance but reduced the spontaneous firing. When the membrane potential was more negative than 70 mV, cesium hyperpolarized the cell, decreased current-evoked firing and increased the input resistance. I_h in DNLL neurons does not contribute to the normal resting potential but may enhance the extent of excitation, thereby making the DNLL a consistently powerful inhibitory source to upper levels of the auditory system.

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