Figure 6. Na⁺ influx through NMDA receptor channels inhibits N-VDCCs in hippocampal neurones.

A, effect of Na⁺ entry through NMDA receptor channels. Aa, I_Ba was measured in a Na⁺-free solution. The double pulse protocol was as in Fig. 5. NMDA (100μm) was applied in the Na⁺-free solution for 65 s, washed out, and immediately I_Ba was measured again. Only the first second of the NMDA record is shown. Ab, continuation of the experiment in the same cell, after shifting to high Na⁺-solution. The currents measured before and after NMDA are shown again in Ac after the scaling up of I_Ba recorded after NMDA to that recorded before NMDA. B, correlation of changes in I_Ba (a) and in facilitation (b) induced by Na⁺ influx through NMDA receptors with the amplitude of NMDA responses. The straight line is a least squares fit, the dashed lines show 95% confidence intervals. C and D, summary of the effects of Na⁺ entry through NMDA receptors on amplitude (C) and facilitation (D) of I_Ba. n= 6 in Na⁺-free solution and n= 7 in high-Na⁺ solution. ***P < 0.001.