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The Journal of Neurophysiology Vol. 84 No. 5 November 2000, pp. 2630-2637
Copyright ©2000 by the American Physiological Society
1Department of Electronic Engineering, Graduate School of Engineering, Osaka University, Suita 565-0871; and 2Division of Biophysical Engineering, Graduate School of Engineering Science and 3Core Research for Evolutional Science and Technology/Murakami Laboratory, Center for Advanced Research Projects, Osaka University, Toyonaka 560-8531, Japan
Song, Wen-Jie,
Yosuke Baba,
Takeshi Otsuka, and
Fujio Murakami.
Characterization of Ca2+ Channels in Rat Subthalamic
Nucleus Neurons. J. Neurophysiol. 84: 2630-2637, 2000. The subthalamic
nucleus (STN) plays a key role in motor control. Although previous
studies have suggested that Ca2+ conductances may
be involved in regulating the activity of STN neurons,
Ca2+ channels in this region have not yet been
characterized. We have therefore investigated the subtypes and
functional characteristics of Ca2+ conductances
in STN neurons, in both acutely isolated and slice preparations.
Acutely isolated STN cells were identified by retrograde filling with
the fluorescent dye, Fluoro-Gold. In acutely isolated STN neurons,
Cd2+-sensitive, depolarization-activated
Ba2+ currents were observed in all cells studied.
The current-voltage relationship and current kinetics were
characteristic of high-voltage-activated Ca2+
channels. The steady-state voltage-dependent activation curves and
inactivation curves could both be fitted with a single Boltzmann function. Currents evoked with a prolonged pulse, however, inactivated with multiple time constants, suggesting either the presence of more
than one Ca2+ channel subtype or multiple
inactivation processes with a single channel type in STN neurons.
Experiments using organic Ca2+ channel blockers
revealed that on average, 21% of the current was nifedipine sensitive,
52% was sensitive to
-conotoxin GVIA, 16% was blocked by a high
concentration of
-agatoxin IVA (200 nM), and the remainder of the
current (9%) was resistant to the co-application of all blockers.
These currents had similar voltage dependencies, but the
nifedipine-sensitive current and the resistant current activated at
slightly lower voltages.
-Agatoxin IVA at 20 nM was ineffective in
blocking the current. Together, the above results suggest that acutely
isolated STN neurons have all subtypes of high-voltage-activated
Ca2+ channels except for P-type, but have no
low-voltage-activated channels. Although acutely isolated neurons
provide a good preparation for whole cell voltage-clamp study,
dendritic processes are lost during dissociation. To gain information
on Ca2+ channels in dendrites, we thus studied
Ca2+ channels of STN neurons in a slice
preparation, focusing on low-voltage-activated channels. In
current-clamp recordings, a slow spike was always observed following
termination of an injected hyperpolarizing current. The slow spike
occurred at resting membrane potentials and was sensitive to micromolar
concentrations of Ni2+, suggesting that it is a
low-threshold Ca2+ spike. Together, our results
suggest that STN neurons express low-voltage-activated
Ca2+ channels and several high-voltage-activated
subtypes. Our results also suggest the possibility that the
low-voltage-activated channels have a preferential distribution to the
dendritic processes.
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