Multiple reversal potentials for responses to L-glutamic acid.

Reversal potentials for L-glutamic and kainic acid were determined from foetal mouse neurones, grown dissociated in culture, and originating either from the brain or spinal cord. Amino acids were applied at known concentrations by pressure microperfusion and responses recorded using conventional intracellular techniques. Altering membranes potential by injecting current through the recording electrode permitted direct (not extrapolated) observation of reversal potentials. Values of reversal potentials differed from previous reports in culture but were still well below those predicted solely from an increase in sodium conductance. Furthermore, with some neurones it was possible to demonstrate multiple phases of response, each phase differing in time course and possessing a separate reversal potential. One reversal potential indicated the participation of potassium conductance in the response.