TY - JOUR T1 - A Calcium-Activated Nonselective Cation Conductance Underlies the Plateau Potential in Rat Substantia Nigra GABAergic Neurons JF - The Journal of Neuroscience JO - J. Neurosci. SP - 6531 LP - 6541 DO - 10.1523/JNEUROSCI.1678-07.2007 VL - 27 IS - 24 AU - Christian R. Lee AU - James M. Tepper Y1 - 2007/06/13 UR - http://www.jneurosci.org/content/27/24/6531.abstract N2 - Plateau potentials can be elicited in nigral GABAergic neurons by injection of 500 ms depolarizing current pulses from hyperpolarized holding potentials in whole-cell recordings in vitro. In approximately one-third of these neurons, plateau potentials were observed under control conditions and could be elicited in the remaining neurons after blocking potassium conductances. Application of the L-type calcium channel agonist Bay K 8644 or activation of NMDA receptors enhanced plateau potentials observed under control conditions and caused a plateau to be elicited in neurons not exhibiting it previously. The plateau potential was abolished in calcium-free buffer, as well as by nickel or cadmium. The L-type calcium channel blockers nimodipine and nifedipine abolished the plateau potential observed under control conditions but did not affect plateaus unmasked by tetraethylammonium. Plateau potentials observed under control conditions as well as those observed in the presence of Bay K 8644, NMDA, or tetraethylammonium were abolished in low-sodium buffer and by the calcium-activated nonselective cation conductance blocker flufenamic acid. These data suggest that nigral plateau potentials are mediated by a calcium-activated nonselective cation conductance (ICAN) that is activated by calcium entry predominantly through L-type calcium channels. In many nigral neurons, ICAN is masked by tetraethylammonium-sensitive potassium conductances, but plateaus can be evoked after increasing calcium conductances. The ICAN-mediated plateau potential in nigral GABAergic neurons likely affects the way these neurons integrate input and may represent a mechanism contributing to the rhythmic firing of these neurons seen in pathological conditions such as Parkinson's disease. ER -