Synthesis and photochemistry of photolabile derivatives of gamma-aminobutyric acid for chemical kinetic investigations of the gamma-aminobutyric acid receptor in the millisecond time region.

The gamma-aminobutyric acid (GABA) receptor is an abundant neuronal receptor in the mammalian and invertebrate nervous systems and is associated with an inhibitory chloride ion channel. GABA is the endogenous neurotransmitter for the receptor and can trigger both fast activation and a reversible desensitization of the receptor. A series of photolabile amine-linked o-nitrobenzyl derivatives of GABA were synthesized that photolyze rapidly to release free GABA. The photochemical properties of the GABA precursors were determined; the compounds undergo rapid photolysis, initiated with UV irradiation at 308 nm, and release free GABA on a millisecond time scale. The pH of the photolysis medium affects both the quantum yield and the rate of photolysis. For example, the quantum yield observed for N-(alpha-carboxy-2-nitrobenzyl)-gamma-aminobutyric acid increases from 0.06 at pH 5.0 to 0.1 at pH 10.5, and the half-life for the photolytic reaction decreases from 1.0 to 2.5 ms in the same pH range. Photolysis of the compounds induces rapid onset of transmembrane ion currents in mouse cortical neurons. The potential of the new compounds for use in rapid chemical kinetic investigations of the neuronal GABA receptor is demonstrated.