Further study on anion permeability of inhibitory post‐synaptic membrane of cat motoneurones

Coombs, Eccles & Fatt (1955) found that, when activated by the transmitter, the inhibitory post-synaptic membrane of cat motoneurones developed a high permeability to chloride and to three other species of anions, but remained impermeable to five other species of anion. Since all ions in this latter category had a larger size in the hydrated state, it was suggested that the activated inhibitory membrane had a sieve-like structure with a critical pore size. This postulate was tested by Araki, Ito & Oscarsson (1961 a, b) for eighteen additional species of anion, seven penetrating and eleven non-penetrating, and, with the exception of the permeability to the formate ions, all results were explicable by the postulate of a critical pore size. In the present investigation the permeability of the activated inhibitory membrane was tested for ten additional species of anion: hydrosulphide, cyanate, hexafluorophosphate (PF6), chromate, monocbloroacetate (CH2C1CO2), iodate, monobromoacetate (CH2BrCO2), benzoate, hypophosphite, lactate.