Early hypoxia does not affect the Na⁺ channel kinetics. A, Na⁺ channel currents during 40 msec depolarizing pulses to a V_r +50 mV from a holding potential of V_r before and after a 4 min hypoxic episode. Currents were recorded in a cell-attached configuration from a representative layer 5 neuron in a 400-μm-thick slice at 37°C. Bottom traces are ensemble Na⁺ currents obtained by averaging 150 sweeps under each condition. B, Ensemble Na⁺currents from a different neuron at different membrane potentials in the control and after 4 min of hypoxia. The patch membrane was held at a V_r −40 mV and stepped to a given test voltage for 20 msec (see inset for C). Here and in A, currents were filtered at 3.5 kHz (−3 dB) and digitized at 20 kHz. Note that 4 min of hypoxia did not alter the availability and properties of Na⁺ channels. The Na⁺ current I–V curve (C) and its conductance transform (D) are not altered by hypoxia.