Figure 5. Internally perfused Sph suppresses K⁺ current.

A, current traces from a representative neuron under control conditions (left) and after a 20 min application of 1 μm Sph (middle). The Sph-sensitive K⁺ current (I_K) was obtained by subtraction of the traces after treatment with Sph from the control (right panel). Currents were obtained with voltage steps in 10 mV increments from −80 to +60 mV from a holding voltage of −60 mV. The current traces presented in these panels are in 20 mV increments (−80 to +60 mV) for purposes of clarity. The calibration bar on the left refers to the left and middle panels, whereas the calibration bar on the right refers to the right panel. The line labelled zero marks the level for zero current. B, left, current–voltage relation for the time-dependent suppression of I_K by Sph in five neurons. The decreases in the currents measured at 6, 10 and 20 min were significantly different from the control for voltages between −10 and +60 mV. B, right, conductance–voltage relation, wherein the conductances at each time were normalized to the fitted value of maximal conductance (G_max) obtained for each neuron under the control condition. The decreases in the values for G/G_max measured at 6, 10 and 20 min were significantly different to the control for voltages between −10 and +60 mV, −10 and +60 mV, and −20 and +60 mV, respectively. C, left, current–voltage relation for the Sph-sensitive I_K, as determined from the subtraction of the current traces obtained after the 20 min exposures to Sph from their respective controls. C, right, normalized current–voltage relation for the Sph-sensitive I_K. Currents were normalized to the peak I_K obtained for the step to +60 mV under control conditions. *Significant difference between the currents obtained for voltages between −10 and +60 mV compared with that at −60 mV (P < 0.05, ANOVA).