Modulation of calcium-activated potassium small conductance (SK) current in rat dopamine neurons of the ventral tegmental area

Block of calcium-sensitive potassium SK current (gKCa [SK]) by apamin or bicuculline methiodide potentiates burst firing in dopamine neurons in the presence of N-methyl- d-aspartate (NMDA). The purpose of this study was to test the hypothesis that calcium entry through NMDA-gated channels can potentiate gKCa [SK] in dopamine neurons in the ventral tegmental area. We used microelectrodes to record an outward tail current that was evoked by membrane depolarization under single-electrode voltage-clamp. Using bicuculline methiodide (50 μM) as a reversible inhibitor of gKCa [SK], we found that NMDA (15 μM) reduced the peak amplitude of the outward tail current by 39%. Contrary to expectations, our results suggest that stimulation of NMDA receptors reduces the calcium-activated potassium gKCa [SK], an effect that could facilitate NMDA-dependent burst firing.