Figure 3. Electrophysiological properties of the background hypoxia-sensitive K⁺ current (I_K,O2) in GPN neurones.

A, traces show a representative example of background or ‘leak’ currents before (Nox), during (Hox) and after (Rec) hypoxia, recorded in symmetrical high K⁺ solution (135 mm) containing TTX (1 μm), 4-AP (5 mm), TEA (30 mm) and Ni²⁺ (2 mm; substituted for Ca²⁺), during various voltage steps from −100 to +70 mV. Corresponding I-V plots are shown on the right. B, I-V plot shows a representative example of the hypoxia-sensitive ‘difference’ current (I_K,O2), obtained by subtracting the current density during hypoxia from that during normoxia (see A). C, I_K,O2 current density was obtained from groups of cells at three different extracellular K⁺ concentrations as follows: 5 mm (n = 4), 75 mm (n = 4) and 135 mm (n = 7); note that for each case the reversal potential of I_K,O2 was similar to that predicted by the Nernst equation for K⁺ (i.e. −80, −14 and 0 mV, respectively).