Fluctuation Analysis of Neutral Amino Acid Responses in Cultured Mouse Spinal Neurones

1. Intracellular recordings using the voltage-clamp technique were made at room temperature (24 +/- 1.5 degrees C) from mouse spinal and sensory neurones growing in dissociated cell culture. 2. Membrane current responses could be elicited by ionophoresis of the neutral amino acids, gamma-aminobutyric acid (GABA), beta-alanine (BALA) and glycine to the cell body and processes of these neurones. 3. All membrane current responses were associated with increases in current fluctuations. Most of the analysis presented here was applied to responses generated at the cell body. 4. Many of the fluctuations in membrane current occurring during the responses could be interpreted as reflecting the kinetic behaviour of a single population of two-state Cl- ion-channels. 5. The properties of channels estimated during the desensitized phase of an amino acid-induced current response were not significantly different from those estimated during the peak of the response. 6. The properties of the amino acid-activated channels were relatively constant over the -40 to -90 mV range of membrane potential. 7. There was considerable variation in the estimated average conductance, gamma, and duration, tau, of the elementary events evoked by the neutral amino acids on spinal cord neurones. The properties of the elementary channel events activated by one of the amino acids were significantly different from those activated on the same neurones by either of the other amino acids. 8. In sensory neurones the average gamma and tau values for GABA-activated ion-channels were also determined and these values fell within the range of those for channels activated by GABA in spinal neurones. 9. The results indicate that different naturally occurring neutral amino acids activate channels with unique properties in cultured mouse spinal neurones. The relative charge transfer associated with these channels averages 1.00:0.74:0.32; GABA:glycine:beta-alanine.