Caesium ions: A glycine-activated channel agonist in rat spinal cord neurones grown in cell culture

1. The chloride (Cl^-) currents activated by caesium ions (Cs⁺), glycine and γ-aminobutyric acid (GABA) were compared following their application to rat neurones that had been grown in cell culture. Recordings were made using the whole-cell patch clamp technique under voltage clamp conditions. 2. In spinal cord neurones, bicuculline methiodide antagonized GABA-activated currents more effectively than Cs⁺- or glycine-activated currents. However, strychnine was more effective at blocking the currents activated by Cs⁺ or glycine than those activated by GABA. 3. Of the 3 agonists, only GABA activated currents in cells from the intermediate lobe of the rat pituitary. 4. In spinal neurones the size of the currents activated by 70 mM Cs⁺ was correlated to the size of the currents activated by 15 μM glycine (P < 0.005; n = 10, Spearman's rank correlation), but there was no significant correlation between the size of the currents activated by these agents and 10 μM GABA. 5. The joint application of glycine and Cs⁺ activated currents that were approximately twice as big as the sums of the currents activated by separate applications of the same doses. This synergism was consistent with Cs⁺ acting at the same receptor as glycine (7 μM glycine being equivalent to 31 ± 7 mM Cs⁺). 6. It was concluded that Cs⁺ activates the same Cl^- channel as the inhibitory neurotransmitter glycine.