Determination of the chemical mechanism of neurotransmitter receptor-mediated reactions by rapid chemical kinetic methods.

When neurotransmitters bind to their specific receptors in the membrane of nerve and muscle cells they induce conformational transitions leading to the formation of open receptor-channels and desensitized receptor forms. A knowledge of the rate and equilibrium constants associated with these transitions is required to (i) relate the mechanism of the receptor-mediated reaction to the resulting changes in transmembrane voltage that trigger signal transmission between neurons, (ii) calculate changes in transmembrane voltage that result from the interaction of diverse excitatory and inhibitory receptors in the same cell, and (iii) understand the mechanism by which receptor function is affected by activators, inhibitors, including clinically important compounds, and diseases of the nervous system. The conformational transitions of interest occur in the millisecond and the sub-millisecond time region. Chemical kinetic techniques for studying reactions mediated by membrane-bound neurotransmitter receptors in cells or vesicles in this time domain were not available. Here we describe the development and use of a laser pulse photolysis technique suitable for chemical kinetic investigations of neurotransmitter receptors in the mu s and ms time region. The type of information that can be obtained is also discussed.