Responses of Xenopus laevis Water Nose to Water-Soluble and Volatile Odorants

Using the whole-cell mode of the patch-clamp technique, we recorded action potentials, voltage-activated cationic currents, and inward currents in response to water-soluble and volatile odorants from receptor neurons in the lateral diverticulum (water nose) of the olfactory sensory epithelium of Xenopus laevis. The resting membrane potential was −46.5 ± 1.2 mV [Formula: see text] , and a current injection of 1–3 pA induced overshooting action potentials. Under voltage-clamp conditions, a voltage-dependent Na(+) inward current, a sustained outward K(+) current, and a Ca(2+)-activated K(+) current were identified. Application of an amino acid cocktail induced inward currents in 32 of 238 olfactory neurons in the lateral diverticulum under voltage-clamp conditions. Application of volatile odorant cocktails also induced current responses in 23 of 238 olfactory neurons. These results suggest that the olfactory neurons respond to both water-soluble and volatile odorants. The application of alanine or arginine induced inward currents in a dose-dependent manner. More than 50% of the single olfactory neurons responded to multiple types of amino acids, including acidic, neutral, and basic amino acids applied at 100 μM or 1 mM. These results suggest that olfactory neurons in the lateral diverticulum have receptors for amino acids and volatile odorants.