IN-VIVO MODIFICATION OF GABA(A) RECEPTOR WITH A HIGH-DOSE OF PYRIDOXAL-PHOSPHATE INDUCES TONIC-CLONIC CONVULSION IN IMMATURE MICE

The biologic cofactor, pyridoxal-5'-phosphate (PLP), is responsible fo r tonic-clonic convulsion in immature mice. The mechanisms underlying such convulsive fits induced by administration of a single high dose o f PLP were studied. The administration of PLP resulted in a 13% increa se of PLP in the P-2 fraction compared to control P-2, and the calcula ted data suggested that membrane bound PLP increased over 31% (similar to 1 mu M). The P-2 fraction of administered mice was treated with [H -3]NaBH4 and analyzed by SDS-polyacrylamide gel electrophoresis. The r adioactivity was mainly incorporated into a 52 kDa protein which corre sponded to a GABA(A) receptor subunit. The addition of PLP in vitro co mpetitively inhibited [H-3]GABA binding as well as [H-3]flunitrazepam binding to synaptic membranes in a concentration-dependent manner, and 50% inhibition was achieved with 1 mM PLP. The results obtained in th e present study demonstrate that PLP was rapidly permeable into the br ain through the immature blood-brain barrier and then bound directly t o GABA(A) receptor. It is probable that specific amino groups of lysin e residues on the GABA(A) receptor react in vivo with PLP to form Schi ff bases, and that the in vivo modification of the receptor produces a degeneration of GABAergic neurotransmission leading to the onset of a convulsive fit.