Anion Permeability of the Olfactory Receptive Membrane

The ionic mechanism of the electropositive olfactory receptor potential was studied in the bullfrog and the swamp frog. The positive receptor potential strikingly decreased in amplitude in chloride-free solution. When the olfactory epithelium was immersed in high-KCl-Ringer's solution and then in Cl-free, high-K solution, the polarity of the positive potential could be reversed. This is supposed to be due to the exit of the increased internal chloride ion. From the above two experiments it is concluded that the positive olfactory receptor potential depends primarily upon the influx of the chloride ion through the olfactory receptive membrane. Some contribution by potassium and possibly other ions may occur. The ability of other anions to substitute for chloride was examined. It was found that only Br(-), F(-), and HCO(2) (-) could penetrate the olfactory receptive membrane. The sieve hypothesis in the inhibitory post-synaptic membrane (Coombs, Eccles, and Fatt, 1955) is not applicable to the olfactory receptive membrane on the basis of the size of hydrated ions, but it may be applicable on the basis of the sizes of naked ions.