Characterization of Ca(2+) channels in rat subthalamic nucleus neurons.
The subthalamic nucleus (STN) plays a key role in motor control. Although previous studies have suggested that Ca(2+) conductances may be involved in regulating the activity of STN neurons, Ca(2+) channels in this region have not yet been characterized. We have therefore investigated the subtypes and functional characteristics of Ca(2+) 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(2+)-sensitive, depolarization-activated Ba(2+) currents were observed in all cells studied. The current-voltage relationship and current kinetics were characteristic of high-voltage-activated Ca(2+) 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 Ca(2+) channel subtype or multiple inactivation processes with a single channel type in STN neurons. Experiments using organic Ca(2+) channel blockers revealed that on average, 21% of the current was nifedipine sensitive, 52% was sensitive to omega-conotoxin GVIA, 16% was blocked by a high concentration of omega-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. omega-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(2+) 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 Ca(2+) channels in dendrites, we thus studied Ca(2+) 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(2+), suggesting that it is a low-threshold Ca(2+) spike. Together, our results suggest that STN neurons express low-voltage-activated Ca(2+) 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.
Song
W J
WJ
Department of Electronic Engineering, Graduate School of Engineering, Osaka University, Suita 565-0871, Japan. song@ele.eng.osaka-u.ac.jp
Baba
Y
Y
Otsuka
T
T
Murakami
F
F
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D001464:Barium / Q000494:pharmacology; D002104:Cadmium / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000502:physiology*; D003712:Dendrites / Q000737:chemistry / Q000502:physiology; D009474:Neurons / Q000737:chemistry* / Q000502:physiology* / Q000648:ultrastructure; D018408:Patch-Clamp Techniques; D051381:Rats; D017207:Rats, Sprague-Dawley; D020531:Subthalamic Nucleus / Q000737:chemistry* / Q000166:cytology* / Q000502:physiology; D020867:omega-Agatoxin IVA / Q000494:pharmacology
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D020867:omega-Agatoxin IVA; D002104:Cadmium; D001464:Barium