Bepridil-induced blockade of NMDA channels in rat hippocampal neurones

Neurones isolated from the CA1 region of rat hippocampal slices by the "vibrodissociation" method were voltage-clamped in the whole-cell configuration. The currents through N-methyl-D-aspartate (NMDA) channels were recorded in response to the rapid application (solution exchange time <30 msec) of 100 microM aspartate (ASP) in a Mg2+-free solution in the presence of 3 microM glycine. When added to the ASP solution, bepridil (BPD) caused a concentration-dependent decrease in both peak and stationary currents due to an uncompetitive open-channel blockade of NMDA channels. At -100 mV, the half-blocking concentration (IC50) for the stationary current was 14.01 +/- 0.17 microM (n = 10). The blocking and unblocking time constants were 7.4 +/- 0.3 x 10(3)/M/sec and 0.12 +/- 0.02/sec, respectively. Membrane hyperpolarization enhanced the BPD block. The equilibrium dissociation constant behaved as an exponential function of the membrane potential and increased e-fold every 37 mV.