Physiological and pharmacological manipulations with light flashes.

In the experiments described here, a physiological measurement is made while photochemical procedures are employed to alter (a) the concentration of a ligand near membranes or proteins or (b) the structure of the ligand-receptor complexes. Because photochemical reactions often provide the quickest way to produce such chemical perturbations, we emphasize the kinetic information that such experiments have yielded. This information requires a suitably rapid physiological measurement, usually an electrical or optical one. The results often complement hose obtained with other kinds of kinetic investigation (iontophoretic application of drugs, stopped-flow mixing, temperature jump, etc). Pharmacological manipulations with light flashes are especially useful for biological systems that cannot be flowed, for instance membranes under electrophysiological investigation or solutions at very low temperatures. In a conceptual sense, this chapter could treat flash-photolysis investigations of heme proteins; but the topic has recently been reviewed authoritatively (84). This review does not concern photoaffinity labeling (28) or studies on fluorescence recovery after photobleaehing.