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The Journal of Neuroscience, March 15, 1999, 19(6):2195-2208
Transient Potassium Currents Regulate the Discharge Patterns of
Dorsal Cochlear Nucleus Pyramidal Cells
Patrick O.
Kanold1, 2 and
Paul B.
Manis1, 2, 3
1 The Center for Hearing Sciences and Departments of
2 Biomedical Engineering and
3 Otolaryngology-Head and Neck Surgery, The Johns
Hopkins University School of Medicine, Baltimore, Maryland 21205
Pyramidal cells in the dorsal cochlear nucleus (DCN) show three
distinct temporal discharge patterns in response to sound: "pauser," "buildup," and "chopper." Similar discharge
patterns are seen in vitro and depend on the voltage
from which the cell is depolarized. It has been proposed that an
inactivating A-type K+ current
(IKI) might play a critical role in
generating the three different patterns. In this study we examined the
characteristics of transient currents in DCN pyramidal cells to
evaluate this hypothesis. Morphologically identified pyramidal cells in
rat brain slices (P11-P17) exhibited the three voltage-dependent
discharge patterns. Two inactivating currents were present in
outside-out patches from pyramidal cells: a rapidly inactivating
(IKIF, ~11 msec) current
insensitive to block by tetraethylammonium (TEA) and variably blocked
by 4-aminopyridine (4-AP) with half-inactivation near 85 mV, and a
slowly inactivating TEA- and 4-AP-sensitive current
(IKIS, ~145 msec) with
half-inactivation near 35 mV. Recovery from inactivation at 34°C
was described by a single exponential with a time constant of 10-30
msec, similar to the rate at which first spike latency increases with
the duration of a hyperpolarizing prepulse. Acutely isolated cells also
possessed a rapidly activating (<1 msec at 22°C) transient current
that activated near 45 mV and showed half-inactivation near 80 mV.
A model demonstrated that the deinactivation of
IKIF was correlated with the discharge patterns. Overall, the properties of the fast inactivating
K+ current were consistent with their proposed role
in shaping the discharge pattern of DCN pyramidal cells.
Key words:
hearing; auditory system; cochlear nucleus; transient
potassium currents; potassium channels; voltage-clamp; intrinsic
discharge patterns; inactivation; outside-out patches
Copyright © 1999 Society for Neuroscience 0270-6474/99/1962195-14$05.00/0
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