In vivo modification of GABAA receptor with a high dose of pyridoxal phosphate induces tonic-clonic convulsion in immature mice.

Abstract The biologic cofactor, pyridoxal-5′-phosphate (PLP), is responsible for tonic-clonic convulsion in immature mice. The mechanisms underlying such convulsive fits induced by administration of a single high dose of PLP were studied. The administration of PLP resulted in a 13% increase of PLP in the P 2 fraction compared to control P 2 , and the calculated data suggested that membrane bound PLP increased over 31% (∼1 μM). The P 2 fraction of administered mice was treated with [ 3 H]NaBH 4 and analyzed by SDS-polyacrylamide gel electrophoresis. The radioactivity was mainly incorporated into a 52 kDa protein which corresponded to a GABAA receptor subunit. The addition of PLP in vitro competitively inhibited [ 3 H]GABA binding as well as [ 3 H]flunitrazepam binding to synaptic membranes in a concentration-dependent manner, and 50% inhibition was achieved with 1 mM PLP. The results obtained in the present study demonstrate that PLP was rapidly permeable into the brain through the immature blood-brain barrier and then bound directly to GABA A receptor. It is probable that specific amino groups of lysine residues on the GABA A receptor react in vivo with PLP to form Schiff bases, and that the in vivo modification of the receptor produces a degeneration of GABAergic neurotransmission leading to the onset of a convulsive fit.