Dopamine-modulated potassium channels on rat striatal neurons: specific activation and cellular expression

Abstract

We have used cell-attached patch-clamp electrophysiology to characterize the activation and distribution of an 85 pS K+ channel on freshly dissociated rat striatal (caudate-putamen) neurons. In recordings from 643 cells, openings of this channel showed an absolute dependence on the presence of dopamine or the D2-like dopamine receptor agonist quinpirole in the cell-attached patch pipette, but were never seen when the D2 antagonist domperidone was applied along with quinpirole, or in the absence of drug. This channel displayed inward rectification at depolarized membrane potentials, but its activation was otherwise voltage insensitive. It was largely restricted to a subset of dissociated cells with diameters > or = 10 microns, with channel openings seen in about 25% of patches. When present, there were typically multiple channels per patch. Cells of this size were immunocytochemically stained for neuron-specific enolase but not glial fibrillary acidic protein; about 40% were also labeled for gamma-amino butyric acid (GABA) and about 60% for NADPH diaphorase, with GABAergic cells displaying a shape most similar to that of cells expressing the channel. A large number of distinct types of other channels were also present, comprising inwardly rectifying channels of 5-35 pS conductance and voltage-activated channels of 100-250 pS, but the frequencies of occurrence and fractional open times of these channels were independent of the presence or absence of dopaminergic agonists. Thus, the 85 pS K+ channel uniquely requires activation by a D2-like dopamine receptor on rat striatal neurons, and is selectively expressed by a subset of these cells, which are most likely to be GABAergic neurons.

Opioid Receptor Modulation of a Metabolically Sensitive Ion Channel in Rat Amygdala Neurons

“…4C). This result contrasts with observations of an 85 pS dopaminemodulated channel in caudate-putamen neurons, where we typically find two to four channels per patch under equivalent conditions (Greif et al, 1995). Consequently, there may be differences in channel or receptor distributions over the surface of the cell membrane between these two systems.…”

“…We have not, however, been able to show that internal ATP gates the channel, because this channel proved unstable in inside-out recordings. However, our results are very similar to those for the 85 pS channel modulated by D 2 dopamine receptors in caudateputamen neurons (Greif et al, 1995). That channel is also activated by rotenone, is sensitive to sulfonylurea drugs in a manner suggestive of a K ATP channel (Lin et al, 1993), and has recently been shown to be directly regulated by ATP (Sun et al, 2000).…”

“…Among the 30 -40 m cells, 31 of 32 observed (97%) were immunoreactive, as were 365 of 420 of the smaller cells (87%); no nonspecific labeling was observed in either cell group when the primary antibody was omitted from the incubation. In contrast, no labeling for glial fibrillary acidic protein was seen in 12 of the larger cells and 158 of the smaller cells, although the same antibody gives positive labeling of some dissociated cells from the caudate-putamen in our hands (Greif et al, 1995). Thus, a large proportion of the dissociated amygdala cells were neurons.…”

“…At voltages negative to the reversal potential, these channels were not depolarizationdependent in their open probabilities. They thus resembled the dopamine receptor-insensitive inward rectifier channels in the caudate-putamen (Greif et al, 1995) except that they included channels of larger conductances. There were also channels of 150 -200 pS, whose open probabilities increased conspicuously as the patch membrane was depolarized (Fig.…”

“…Amygdala neurons were freshly dissociated by methods similar to those previously described (Greif et al, 1995;Chen et al, 2000). Male rats (Sprague Dawley VAF; Charles River Laboratories, Wilmington, M A), 30 -45 d old, were killed by rapid decapitation, and the brains were rapidly and gently removed into an ice-cold solution of (in mM): NaC l, 124; KC l, 4; C aC l 2 , 1; MgCl 2 , 1; MnCl 2 , 0.02; D-glucose, 25; and PI PES-Na, 20, pH 7.0, equilibrated with O 2 .…”