The reversal potential as a diagnostic tool in transmitter identification.

The three-ion test still appears to be the best electrophysiological tool available to define the molecular mechanisms involved in activation of a given ionophore. New insights into synaptic mechanisms require the investigator to be alert to possible exceptional cases. In general, the treatment of the exceptional case is validly accomplished once the diagnosis is made. It is important to determine the Nernstian behavior of the reversal potential and to identify the ions that participate in the synaptic process, as well as to determine whether the conductances for these ions increase or decrease. Noise analysis, although measuring properties of the synaptic ionophore, seems the most promising physiological tool for identification of the transmitter recognition moiety of the receptor, since the open time appears to be a function of binding. It remains to develop stringent methodology for analyzing channel open time during the physiological event.