Figure 6. Oligodendrocyte precursor glia with and without I_Na respond differently to ischaemia.

a Response of a P7 OPC lacking I_Na to simulated ischaemia (0 mM Mg²⁺ enhances detection of NMDA receptor currents, -40 mV), and block of glutamate-mediated component of current by 200 μM AP5 and 25 μM NBQX. b As a, but for a cell with I_Na, showing spontaneous synaptic currents (circles) contribute to the response. The greater noise in the trace for the I_Na cell reflects the presence of synaptic input which is lacking in the no I_Na cell, and the presence of a larger number of glutamate-gated channels in the I_Na cell. c Ischaemia-evoked inward current and current suppressed by glutamate receptor blockers (at 500-800 sec after starting ischaemia, ± s.e.m.) in I_Na and no I_Na cells_. Analysing the current inhibition as a percentage of the ischaemia-induced current showed the same difference between the I_Na and no I_Na cells: in I_Na cells the inhibition was 71.5 ± 9.7% of the ischaemia-evoked current, while in no I_Na cells it was 24.0 ± 15.2% (significantly different, P = 0.035). d Frequency of inward and outward spontaneous synaptic currents at -40 mV in 4 cells after 1 min ischaemia (relative to pre-ischaemia). Cs-gluconate internal, E_Cl -87 mV, in a-d. e Labelling of P7 slice for NG2 (green), Na⁺ channels (red, or yellow/orange where overlapping with NG2) and with propidium iodide (mauve) after 1 hour’s ischaemia, showing death of an I_Na cell and no death of a no I_Na cell. f Percentage of NG2 positive I_Na cells and no I_Na cells killed in control conditions (no ischaemia, 103 NG2 expressing cells), after 1 hour’s ischaemia (166 cells), or after 1 hour’s ischaemia in the presence of 25 μM NBQX, 50 μM D-AP5, 50 μM MK-801 and 100 μM 7-chlorokynurenate (7-CK) (173 cells). All P values are for comparison with I_Na cells in ischaemia without blockers.