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.
APStracts 4:127N, 1997.
ABSTRACT
The hyperpolarization-activated current (Ih) 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 æm 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 (Ih) was voltage- and time-dependent. The current was just seen at a
membrane potential of -70 mV and was fully activated at -140 mV. The voltage
value of half-maximal activation of Ih was -78.0ñ6.0 (SE) mV. The rate of Ih
activation was best approximated by a single exponential function with a time
constant that was voltage dependent, ranging from 276ñ27 ms at -100 mV to
186ñ11 ms at -140 mV. Reversal potential (Eh) of Ih current was more positive
than the resting potential. Raising the extracellular potassium concentration
shifted Eh to a more depolarized value, while lowering the extracellular
sodium concentration shifted Eh in a more negative direction. Ih was
sensitive to extracellular cesium but relatively insensitive to extracellular
barium. The current amplitude near maximal-activation (ÿ7E -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 (ÿ7E -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 below -70 mV cesium hyperpolarized the cell, decreased current-
evoked firing and increased the input resistance. Ih 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.
Received 13 November 1996; accepted in final form 1 July 1997.
APS Manuscript Number J894-6.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 24 July 1997