Characterization of Ca 21 Channels in Rat Subthalamic Nucleus Neurons WEN-JIE SONG, 1 YOSUKE BABA, 2 TAKESHI OTSUKA, 1 AND FUJIO MURAKAMI 2,3 1 Department of Electronic Engineering, Graduate School of Engineering, Osaka University, Suita 565-0871; and 2 Division of Biophysical Engineering, Graduate School of Engineering Science and 3 Core Research for Evolutional Science and Technology/Murakami Laboratory, Center for Advanced Research Projects, Osaka University, Toyonaka 560-8531, Japan Received 26 April 2000; accepted in final form 28 July 2000 Song, Wen-Jie, Yosuke Baba, Takeshi Otsuka, and Fujio Murakami. Characterization of Ca 21 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 sug- gested that Ca 21 conductances may be involved in regulating the activity of STN neurons, Ca 21 channels in this region have not yet been char- acterized. We have therefore investigated the subtypes and functional characteristics of Ca 21 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, Cd 21 -sensitive, depolarization-activated Ba 21 currents were observed in all cells studied. The current-voltage relation- ship and current kinetics were characteristic of high-voltage–activated Ca 21 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 mul- tiple time constants, suggesting either the presence of more than one Ca 21 channel subtype or multiple inactivation processes with a single channel type in STN neurons. Experiments using organic Ca 21 channel blockers revealed that on average, 21% of the current was nifedipine sensitive, 52% was sensitive to v-conotoxin GVIA, 16% was blocked by a high concentration of v-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. v-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 Ca 21 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 informa- tion on Ca 21 channels in dendrites, we thus studied Ca 21 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 Ni 21 , suggesting that it is a low-threshold Ca 21 spike. Together, our results suggest that STN neurons express low-voltage–activated Ca 21 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. INTRODUCTION The subthalamic nucleus (STN), the only excitatory nucleus in the basal ganglia, directly excites both output structures of the basal ganglia: the substantia nigra reticulata and the internal globus pallidus (Kita et al. 1983; Kita and Kitai 1987, 1991; Van der Kooy and Hattori 1980; see Kitai and Kita 1987 for review). Since the discovery of the association of hemiballism with pathologic changes in the STN (Whittier 1947), the STN has been recognized as playing a vital role in voluntary move- ment control (see Mink and Thach 1993; Wichmann and De- Long 1996 for reviews). This notion is strongly supported by findings from animal experiments in which blockade of the activity of STN neurons induces severe motor disorders (Hamada and Hasegawa 1996; Wichmann et al. 1994). Given the importance of the STN in motor control, it is of general interest to understand how the activity of STN neurons is regulated. The electrical activity of a neuron is driven by its synaptic inputs and shaped by the intrinsic properties of the cytoplasmic membrane. It has been shown that STN neurons receive excitatory inputs from the cerebral cortex (Bevan et al. 1995; Fujimoto and Kita 1993; Hartmann-von Monakow et al. 1978; Kitai and Deniau 1981; Nambu et al. 1996) and the thalamus (Bevan et al. 1995; Feger et al. 1994; Mouroux and Feger 1993), and inhibitory inputs from the globus pallidus (Groenewegen and Berendse 1990; Moriizumi and Hattori 1992). Several studies have examined the membrane properties of STN neurons. In a pioneering study, Nakanishi et al. (1987) studied the response of STN neurons to current injections in an acutely prepared slice preparation. Several other studies there- after also examined the response properties of STN neurons in acutely prepared slices (Beurrier et al. 1999; Bevan and Wilson 1999; Overton and Greenfield 1995; Song et al. 1998) and in cultured slices (Plenz and Kitai 1999). In all these works, the importance of Ca 21 conductances in the regulation of STN neuron activity was invariably noticed. Ca 21 conductances were suggested to be involved in the generation of a plateau- like potential (Beurrier et al. 1999; Nakanishi et al. 1987; Song et al. 1998), in the generation of rebound activities of STN neurons (Beurrier et al. 1999; Overton and Greenfield 1995; Plenz et al. 1997; Song et al. 1998), and in the regulation of Ca 21 -dependent conductances (Beurrier et al. 1999; Bevan and Address for reprint requests: W.-J. Song, Dept. of Electronic Engineering, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita 565-0871, Japan (E-mail: [email protected]). The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked ‘‘advertisement’’ in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. 2630 0022-3077/00 $5.00 Copyright © 2000 The American Physiological Society www.jn.physiology.org Downloaded from journals.physiology.org/journal/jn (027.079.076.086) on May 11, 2023.
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