Figure 2.

Tonic and phasic blockade of Na⁺ current by ketamine in somata. (a) Recordings of Na⁺ current in the control solution and in the presence of 100, 300, and 1000 μM ketamine. Holding potential was set to −80 mV and Na⁺ currents were activated by 50-ms voltage steps to −20 mV after a 50-ms prepulse to −120 mV. (b) Concentration dependence of the Na⁺ current suppression by ketamine and its enantiomers (8 somata). The data points were fitted using equation (1). IC₅₀ values are given in Table 1. Error bars indicate s.e. if exceeding symbol size. (c) Normalized amplitudes of Na⁺ currents recorded in control solution and in the presence of 100 μM ketamine as a function of pulse number. The currents were activated by a 10-ms voltage step to −20 mV at a frequency of 10 Hz. Holding potential was −80 mV. Each current was normalized to the amplitude of the first Na⁺ current recorded in control solution (10 somata). (d) Effects of ketamine on Na⁺ currents assessed by shifts in the steady-state availability curve. Each symbol represents the mean normalized fractional current derived from at least five different experiments. The data points were fitted by equation (2).