The subthalamic nucleus (STN) plays a key role in motor control. Although p
revious studies have suggested that Ca2+ conductances may be involved in re
gulating the activity of STN neurons, Ca2+ channels in this region have not
yet been characterized. We have therefore investigated the subtypes and fu
nctional characteristics of Ca2+ conductances in STN neurons, in both acute
ly isolated and slice preparations. Acutely isolated STN cells were identif
ied by retrograde filling with the fluorescent dye, Fluoro-Gold. In acutely
isolated STN neurons, Cd2+-sensitive, depolarization-activated Ba2+ curren
ts were observed in all cells studied. The current-voltage relationship and
current kinetics were characteristic of high-voltage-activated Ca2+ channe
ls. The steady-state voltage-dependent activation curves and inactivation c
urves could both be fitted with a single Boltzmann function. Currents evoke
d with a prolonged pulse, however, inactivated with multiple time constants
, suggesting either the presence of more than one Ca2+ channel subtype or m
ultiple inactivation processes with a single channel type in STN neurons. E
xperiments using organic Ca2+ channel blockers revealed that on average, 21
% of the current was nifedipine sensitive, 52% was sensitive to omega -cono
toxin 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-app
lication 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 b
locking the current. Together, the above results suggest that acutely isola
ted STN neurons have all subtypes of high-voltage-activated Ca2+ channels e
xcept for P-type, but have no low-voltage-activated channels. Although acut
ely isolated neurons provide a good preparation for whole cell voltage-clam
p study, dendritic processes are lost during dissociation. To gain informat
ion on Ca2+ channels in dendrites, we thus studied Ca2+ channels of STN neu
rons in a slice preparation, focusing on low-voltage-activated channels. In
current-clamp recordings, a slow spike was always observed following termi
nation of an injected hyperpolarizing current. The slow spike occurred at r
esting membrane potentials and was sensitive to micromolar concentrations o
f Ni2+, suggesting that it is a low-threshold Ca2+ spike. Together, our res
ults suggest that STN neurons express low-voltage-activated Ca2+ channels a
nd several high-voltage-activated subtypes. Our results also suggest the po
ssibility that the low-voltage-activated channels have a preferential distr
ibution to the dendritic processes.