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

Abstract

We present the first electrophysiological evidence for electrogenic ion transport across the frog olfactory mucosa in vitro . When the isolated dorsal mucosa was placed in an Ussing chamber and bathed symmetrically in amphibian Ringer's, the ciliated side became electronegative (V = −5.2 mV ± 0.7 mV). The resistance of the mucosal preparation was 148 ± 4 Ω cm ² . The true short-circuit current was obtained as the intersection of the I–V curve with the current axis after correcting for the series solution resistance. The average value of the short-circuit current was 35.9 μA/cm ² . The I–V relation was linear over the applied potential range of ± 16mV. The magnitude of the specific resistance of the olfactory mucosa is comparable to values reported for various actively transporting respiratory and oral cavity epithelia. Because the geometrical area of the aperture used to normalize both the short-circuit current and the resistance undoubtedly underestimates the actual area of the dorsal olfactory epithelium, the specific resistance and the short-circuit current are probably underestimated and overestimated, respectively. Therefore, the nominally low resistance need not imply a leaky epithelium. Substitution of NO ₃⁻ for Cl ⁻ caused the current to increase and the resistance to decrease. These results suggest that cation absorption plays a role in the sign of the short-circuit current. The in vitro preparation responded to the odorant ethyl n -butyrate by giving an electro-olfactogram (EOG)-like voltage transient which was superimposed on the steady-state potential created by active ion transport. The significance of these results is discussed from the perspective of the peripheral events surrounding olfactory transduction.