Unique Properties of R-Type Calcium Currents in Neocortical and Neostriatal Neurons

1 Department of Anatomy and Neurobiology, University of Tennessee, Memphis, Tennessee 38163; and 2 Department of Physiology, Northwestern University Medical School, Chicago, Illinois 60611 Foehring, Robert C., Paul G. Mermelstein, Wen-Jie Song, Sasha Ulrich, and D. James Surmeier. Unique Properties of R-Type Calcium Currents in Neocortical and Neostriatal Neurons. J. Neurophysiol. 84: 2225-2236, 2000. Whole cell recordings from acutely dissociated neocortical pyramidal neurons and striatal medium spiny neurons exhibited a calcium-channel current resistant to known blockers of L-, N-, and P/Q-type Ca 2+ channels. These R-type currents were characterized as high-voltage-activated (HVA) by their rapid deactivation kinetics, half-activation and half-inactivation voltages, and sensitivity to depolarized holding potentials. In both cell types, the R-type current activated at potentials relatively negative to other HVA currents in the same cell type and inactivated rapidly compared with the other HVA currents. The main difference between cell types was that R-type currents in neocortical pyramidal neurons inactivated at more negative potentials than R-type currents in medium spiny neurons. Ni 2+ sensitivity was not diagnostic for R-type currents in either cell type. Single-cell RT-PCR revealed that both cell types expressed the 1E mRNA, consistent with this subunit being associated with the R-type current.