Single channel properties of NMDA receptors in cortical neurons

The cell-attached and inside-out configurations of the patch-clamp techniques were used to investigate single channel properties of NMDA receptors in cultured intact neurons mechanically isolated from rat cereberal cortex. Recordings were made in Mg2+-free solutions. A channel, with a conductance of 35 pS was studied in detail with either NMDA or L-aspartate in the patch pipette. NMDA channels were permeableic Na+ and K+, but not to Cl-, the mean open times and open probabilities of these channels were decreased with increasing hyperpolarization. Distributions for the open times, closed times and burst durations required two-component fits. Channel openings were suppressed by APV. When Mg2+ was included in the pipette, the mean open times were significantly diminished in a concentration- and voltage- dependent manner. Decreasing the bath temperature prolonged channel open times and decreased current amplitudes. The results indicate that there is an intrinsic voltage dependence of NMDA channel kinettes in the intact neurons, suggesting that the normal function of the NMDA channel may be dependent on some intracellular biochemical processes.