PERMEATION AND BLOCK OF DOPAMINE-MODULATED POTASSIUM CHANNELS ON RAT STRIATAL NEURONS BY CESIUM AND BARIUM IONS

1. In cell-attached patch-clamp recordings from freshly dissociated ra t caudate-putamen neurons, an 85-pS inwardly rectifying K+ channel, wh ich was previously found to be modulated by D-2-like dopamine receptor s, was blocked by externally applied BaCl2 or CsCl. 2. At concentratio ns between 100 and 500 mu M, Ba2+ blockade was voltage dependent, with a greater block at hyperpolarized voltages, in a manner consistent wi th blockade of the channel pore. Single-channel currents were flickery , with intervening periods of more complete blockade, and block appear ed to be time dependent, with an estimated electrical distance of 0.24 and an apparent dissociation constant of 205 mu M at 0 mV. 3. At conc entrations between 1 and 3 mM, Cs+ blockade was similarly voltage depe ndent, but without periods of longer blockade, with an electrical dist ance of 0.81 and an apparent dissociation constant of 625 mu M at 0 mV . Cs+ could also permeate this channel at voltages near the K+ reversa l potential. The current-voltage relationship displayed an anomalous n egative slope conductance, in a manner inconsistent with a single-ion pore. 4. Smaller-conductance, dopamine-insensitive channels were block ed more potently by both Ba2+ and Cs+ than was the 85-pS channel, refl ecting differences between inwardly rectifying K+ channels mediating r esting conductance and those mediating dopamine receptor responses in striatal neurons.