ANION PERMEABILITY OF THE INHIBITORY SUBSYNAPTIC MEMBRANE OF THE SPINAL MOTONEURON OF THE TOAD

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1. Single microelectrodes filled with solutions containing various anions were inserted into toad spinal motoneurons and used for both the electrophoretic injection of anions and for intracellular recording.
2. Judging from the effect of anion injections on the IPSP's, the activated inhibitory subsynaptic membrane was found to be permeable to Br^-, I^-, Cl^-, No₂^-, NO₃^-, N₃^-, ClO₄^-, SCN^-, OCN^-, ClO₃^-, and HCO₂^- ions. 3. BrO₃^-, F^-, HSO₃^-, HCO₃^-, CH₃CO₂^-, SO₄^2-, H₂PO₄^-, HPO₄^2- and citrate ions were found to be impermeable through the activated inhibitory subsynaptic membrane. The ineffectiveness of injection of HS^- ions on the IPSP was confirmed.
4. The time constants of the IPSP recovery after injections were evaluated for nine penetrating anions. Then a sequence was determined for the order of their relative ability to penetrate the motoneuron membrane: It is Br^->OCN^->NO₃^->NO₂^->SCN^->Cl^->HCO₂^->I^-> ClO₃^-.
5. Results obtained in the present investigation were compared with those from studies on cat spinal motoneurons and goldfish Mauthner cells.