Newly synthesized photolabile derivatives of glutamate, caged glutamate, that release free glutamate on a microsecond time scale after a pulse of UV laser light are described. 2-Nitrobenzyl derivatives were attached to the amino or carboxyl groups of glutamate. Substitution with a -COj group at the benzylic carbon accelerates the photolysis reaction when compared to -H and -CH3 substituents. y-O-(aCarboxy-2.nitrobenzyl)glutamate is stable at neutral pH. In 100 mM phosphate buffer at pH 7.0, the compound is photolyzed at 308 nm with a quantum product yield of 0.14.

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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.

A series of photolabile o-nitrobenzyl derivatives of serotonin (caged serotonin) were synthesized: the amine-linked serotonin derivatives N-(2-nitrobenzyl) serotonin (Bz-5HT) and N-(alpha-carboxy-2-nitrobenzyl) serotonin (N-CNB-5HT), and O-alpha-carboxy-2-nitrobenzyl) serotonin (O-CNB-5HT), which has the caging group attached to the phenolic OH group. All the derivatives released free serotonin when excited by 308-nm or 337-nm laser pulses. The time constant of serotonin release from N-CNB-5HT was 1. 2 ms, with a quantum yield of 0.08. This is too slow for rapid chemical kinetic measurements. O-CNB-5HT is suitable for transient kinetic investigations of the serotonin 5-HT(3) receptor. It released serotonin with a time constant of 16 micros and a quantum yield of 0.03. The biological properties of O-CNB-5HT were evaluated, and the applicability of the compound for kinetic studies of the 5-HT(3) receptor was demonstrated. O-CNB-5HT does not activate the 5-HT(3) receptor by itself, nor does it modulate the response of a cell when co-applied with serotonin. When irradiated with a 337-nm laser pulse, O-CNB-5HT released free serotonin that evoked 5-HT(3) receptor-mediated whole-cell currents in NIE-115 mouse neuroblastoma cells.

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