Laser-pulse photolysis studies of chemical reactions in the brain

Membrane-bound receptor proteins regulate the transmission of signals at the junctions between cells of the mammalian nervous system. Upon binding a specific neurotransmitter these receptor proteins form transient (similar to 1 ms) channels through which Inorganic ions flow, leading to a change in the transmembrane voltage of a cell. A newly developed laser-pulse photolysis technique, with a mu s time resolution, allows one to determine the rate constants for both the formation and closing of the transmembrane channel, the dissociation constant for the ligand-binding site that controls channel opening, and the concentration of the receptor in the cell membrane, and gives information about the rate of transient inactivation (desensitization) of the receptor. The technique allows one to determine the binding constants of inhibitors to the closed-and open-channel forms independently. The use of the chemical kinetic method is illustrated.