Fig. 8.
Low-voltage-activated potassium current (ILV) comprised α-DTX-sensitive and linopirdine-sensitive components. A–D: whole cell currents recorded in perforated-patch mode (27°C) from a transient neuron (P10, rat) in response to a family of voltage steps. A: family of currents evoked by a standard voltage protocol (bottom): prepulse to −125 mV followed by steps between −105 and −15 mV, control (Liebovitz-15 [L-15]) external solution. The cell had INa, IA, IHV, and ILV (as in Fig. 7A). B: currents at the onset of a depolarizing step in: L-15 (black), L-15 containing 100 nM a-dendrotoxin (α-DTX, red), and L-15 containing 100 nM α-DTX + 10 μM linopirdine (dark gray). C: I–V relations taken 100 ms after the onset of voltage steps, from the cell in B. Low-voltage (LV) currents (at potentials negative to −30 mV) were partly suppressed in α-DTX (red circles) and strongly suppressed in α-DTX + linopirdine (triangles). D and E: α-DTX-sensitive and linopirdine-sensitive components of ILV activated over different timescales. D: α-DTX blocked a fast component (bottom panel; obtained by subtraction from curves above). The slow remaining component was blocked by linopirdine (E). Activation was fit with single-exponential functions (red curves) with τ values of 4.3 ms for the α-DTX-sensitive component (D, bottom), 96 ms for the α-DTX-insensitive component (E, top), and 72 ms for the linopirdine-sensitive component (E, bottom). Currents in D and E are from 2 cells, different from the cell in A–C. F: conductance–voltage (g–V) relations for the α-DTX-sensitive current (circles) and linopirdine-sensitive current (triangles). Curves: Boltzmann fits (Eq. 1; methods). G: Boltzmann fits to g–V curves, normalized by maximum conductance for each curve (thin red lines, α-DTX-sensitive conductance; thin black lines, linopirdine-sensitive conductance). Thick red and thick black lines: average g–V curves for α-DTX-sensitive current (half-maximum activation voltage [V1/2] = −44 ± 0.2 mV, slope factor [S] = 7.1 ± 0.20 mV, n = 7) and linopirdine-sensitive current (V1/2 = −41 ± 0.3 mV, S = 7.4 ± 0.41 mV, n = 5), respectively. H: activation time constants were much faster for α-DTX-sensitive currents (red circles, n = 8 neurons, some at multiple voltages) than those for α-DTX-insensitive currents (gray triangles, n = 6) and linopirdine-sensitive currents (open down triangles, n = 3). All data in this figure were taken at room temperature, P9–P15.