THE VOLTAGE-SENSITIVE CA2-AGA-IVA AND OMEGA-CTX-MVIIC INHIBIT SPONTANEOUS EPILEPTIFORM DISCHARGES IN THE RAT CORTICAL WEDGE( CHANNEL (VSCC)ANTAGONISTS OMEGA)

The ability of VSCC antagonists to modulate excitatory amino acid (EAA ) release was evaluated by measuring N-methyl-D-aspartate (NMDA) recep tor-dependent spontaneous epileptiform discharges in rat cortical wedg es. The N-type channel blocker omega-CTX-GVIA (300 nM) was ineffective . The P-type channel blocker omega-Aga-IVA at 300 nM reduced the frequ ency of discharges by 63%, while 300 nM omega-CTX-MVIIC reduced the fr equency by 35%. These results coupled with the absence of NMDA antagon ism by omega-Aga-IVA or omega-CTX-MVIIC in the cortical wedge suggest that the VSCCs blocked by these toxins are primarily responsible for m ediating impulse dependent EAA release in the rat neocortex.