Inwardly rectifying potassium (IRK) currents are correlated with IRK subunit expression in rat nucleus accumbens medium spiny neurons

Inwardly rectifying K⁺ (IRK) channels are critical for shaping cell excitability. Whole-cell patch-clamp and single-cell RT-PCR techniques were used to characterize the inwardly rectifying K + currents found in projection neurons of the rat nucleus accumbens. Inwardly rectifying currents were highly selective for K⁺ and blocked by low millimolar concentrations of Cs⁺ or Ba²⁺. In a subset of neurons, the inwardly rectifying current appeared to inactivate at hyperpolarized membrane potentials. In an attempt to identify this subset, neurons were profiled using single-cell RT-PCR. Neurons expressing substance P mRNA exhibited noninactivating inward rectifier currents; whereas neurons expressing enkephalin mRNA exhibited inactivating inward rectifier currents. The inactivation of the inward rectifier was correlated with the expression of IRK1 mRNA. These results demonstrate a clear physiological difference in the properties of medium spiny neurons and suggest that this difference could influence active state transitions driven by cortical and hippocampal excitatory input.