L-AP4 inhibits high voltage-activated Ca2+ currents in pyramidal cortical neurones

We tested the ability of L-AP4 to modulate high voltage-activated (HVA) calcium (Ca2+) currents in pyramidal neurones acutely isolated from the adult rat (4-8 weeks). Whole cell recordings, with barium (Ba2+) ions as the charge carrier, were performed. L-AP4 reduced HVA Ca2+ conductances in 86% of the recorded cells. Saturating concentrations of L-AP4 inhibited about 21% of the current (+/- 8.3%, n = 8), although great variability was observed. Interestingly, low micromolar concentrations of (1S,3R)-1-aminocyclo-pentane-1,3-dicarboxylic acid (1S,3R-ACPD) and (2S,3S,4R)-alpha-(carboxy-cyclopropyl)-glycine (1-CCGI) had weaker effects than L-AP4. MAP4 fully antagonized the L-AP4-mediated reduction of HVA Ca2+ currents. These findings suggest the involvement of the AP4-sensitive receptor in the control of both cellular excitability and transmitter release in rat neocortical neurones.