DOPAMINE-MODULATED POTASSIUM CHANNELS ON RAT STRIATAL NEURONS - SPECIFIC ACTIVATION AND CELLULAR EXPRESSION

We have used cell-attached patch-clamp electrophysiology to characteri ze the activation and distribution of an 85 pS K+ channel on freshly d issociated rat striatal (caudate-putamen) neurons, in recordings from 643 cells, openings of this channel showed an absolute dependence on t he presence of dopamine or the D-2-like dopamine receptor agonist quin piroie in the cell-attached patch pipette, but were never seen when th e D-2 antagonist domperidone was applied along with quinpirole, or in the absence of drug, This channel displayed inward rectification at de polarized membrane potentials, but its activation was otherwise voltag e insensitive, It was largely restricted to a subset of dissociated ce lls with diameters greater than or equal to 10 mu m, with channel open ings seen in about 25% of patches, When present, there were typically multiple channels per patch, Cells of this size were immunocytochemica lly stained for neuron-specific enolase but not glial fibrillary acidi c protein; about 40% were also labeled for gamma-amino butyric acid (G ABA) and about 60% for NADPH diaphorase, with GABAergic cells displayi ng a shape most similar to that of cells expressing the channel, A lar ge number of distinct types of other channels were also present, compr ising inwardly rectifying channels of 5-35 pS conductance and voltage- activated channels of 100-250 pS, but the frequencies of occurrence an d fractional open times of these channels were independent of the pres ence or absence of dopaminergic agonists, Thus, the 85 pS K+ channel u niquely requires activation by a D-2-like dopamine receptor on rat str iatal neurons, and is selectively expressed by a subset of these cells , which are most likely to be GABAergic neurons.