Effects of isoflurane on Na⁺ channel current–voltage (I-V) relations and activation. Chinese hamster ovary cells expressing various rat Na⁺ channel α-subunit isoforms were subjected to whole cell patch clamp recording. Voltage of peak I_Na activation (V_max) was 0 mV for Na_v1.2 (A), −10 mV for Na_v1.4 (B), and −30 mV for Na_v1.5 (C). Isoflurane (0.8 mm, approximately 2.2 times minimum alveolar concentration28) inhibited all three isoforms. Data were fitted to a Boltzmann equation yielding voltage of 50% maximal activation (V_1/2a) and slope factor (k) values. Isoflurane had no effect on V_1/2a. Protocol: 100-ms prepulse from a holding potential of −100 mV, 25-ms test potential from −60 to +80 mV in 10-mV increments, pulses applied at 5-s intervals. Mean isoflurane concentrations were 0.82 ± 0.06 mm for Na_v1.2, 0.78 ± 0.06 mm for Na_v1.4, and 0.81 ± 0.05 mm for Na_v1.5 (mean ± SEM, n = 4–7).