Fig. 1.

Morphology and current profiles of ORAs and VRAs.A, Imaging of a freshly isolated astrocyte during recording with Lucifer yellow dye (0.3%), in the pipette, showing bushy processes extending from the cell body. The processes are not very distinct because there is some folding back of the processes and because of the out-of-focus fluorescence halo, as this photograph was taken through the nonconfocal Nikon Diaphot microscope we used in the recording set up. B, E, Membrane currents induced by voltage steps (50 msec) from −160 to +60 mV (20 mV increments) with a NO₃⁻-based pipette solution (see Materials and Methods). ORAs (B) are characterized by a dominant expression of outwardIK_a and IK_dr plus small inward INa⁺ currents (seeinset below B). VRAs (E) are characterized by a symmetric expression of inward and outward potassium currents. C,F, When K⁺ channel-mediated currents were completely masked by the substitution of pipette K⁺ with Cs⁺, an ORA (C) and a VRA (F) were identified based on their identical bushy morphology but marked different membrane capacitances (10.5 pF in recording Cand 38 pF in F). TheINa⁺ is shown in higher resolution inC. INa⁺ currents were never observed in VRAs (F). D andG are recordings C and F, respectively, at higher resolution and after off-line compensation for leak and capacitance.