Evidence for electrogenic active ion transport across the frog olfactory mucosa in vitro

We present the first electrophysiological evidence for electrogenicion transport across the frog olfactory mucosa in vitro. Whenthe isolated dorsal mucosa was placed in an Ussing chamber andbathed symmetrically in amphibian Ringer's, the ciliated sidebecame electronegative (V = –5.2 mV ± 0.7 mV).The resistance of the mucosal preparation was 148 ± 4 cm². The true short-circuit current was obtained as the intersectionof the I–V curve with the current axis after correctingfor the series solution resistance. The average value of theshort-circuit current was 35.9 µA/cm². The I–V relationwas linear over the applied potential range of ± 16mV.The magnitude of the specific resistance of the olfactory mucosais comparable to values reported for various actively transportingrespiratory and oral cavity epithelia. Because the geometricalarea of the aperture used to normalize both the short-circuitcurrent and the resistance undoubtedly underestimates the actualarea of the dorsal olfactory epithelium, the specific resistanceand the short-circuit current are probably underestimated andoverestimated, respectively. Therefore, the nominally low resistanceneed not imply a leaky epithelium. Substitution of NO₃^–for Cl^– caused the current to increase and the resistanceto decrease. These results suggest that cation absorption playsa role in the sign of the short-circuit current. The in vitropreparation responded to the odorant ethyl n-butyrate by givingan electro-olfactogram (EOG)-like voltage transient which wassuperimposed on the steady-state potential created by activeion transport. The significance of these results is discussedfrom the perspective of the peripheral events surrounding olfactorytransduction.