The ability of a frog olfactory receptor neurone (ORN) to respond to odorous molecules depends on its resting membrane properties, including membrane resistance and potential. Quantification of these properties is difficult because of a shunt conductance at the membrane–pipette seal that is in parallel with the true membrane conductance. In physiological salines, the sum of these two conductances averaged 235 pS. We used ionic substitution and channel blockers to reduce the membrane conductance as much as possible. This yielded a lower limit for the membrane conductance of 158 pS. The upper limit of resting membrane resistance, then, is 6 GΩ. The membrane is permeable to K+ and, to a lesser extent, other cations. No resting Cl− conductance was detectable. Correcting measured zero-current potentials for distortion by the shunt suggests that the resting membrane potential is no more negative than −75 mV. The present results help to explain why frog ORNs are excitable at rest.
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