title: Hypertonicity augments bullfrog taste nerve responses to inorganic salts.
abstract: The tonicity of taste stimulating solutions has been usually ignored, though taste substances themselves yielded the tonicity. We investigated the effect of hypertonicity on bullfrog taste nerve responses to inorganic salts by adding nonelectrolytes such as urea and sucrose that elicited no taste nerve responses. Here, we show that hypertonicity alters bullfrog taste nerve-response magnitude and firing pattern. The addition of urea or sucrose enhances the taste nerve-response magnitude to NaCl and shifts the concentration-response curve to the left. The effect of hypertonicity on responses to CaCl(2) is bimodal; hypertonicity suppresses CaCl(2) responses at concentrations less than ~30 mM and enhances them at concentrations greater than ~30 mM. The hypertonicity also enhances response magnitude to other monovalent salts. The extent of the enhancing effects depends on the difference between the mobility of the cation and anion in the salt. We quantitatively suggest that both the enhancing and suppressing effects result from the magnitude and direction of local circuit currents generated by diffusion potentials across tight junctions surrounding taste receptor cells.
authors.affiliation: Graduate School of Life Science and Systems Engineering, Kyushu Institute of Technology, Kitakyushu 808-0196, Japan.
authors.forename: Namie
authors.initials: N
authors.lastname: Beppu
authors.forename: Yoko
authors.initials: Y
authors.lastname: Higure
authors.forename: Kazunori
authors.initials: K
authors.lastname: Mashiyama
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Ohtubo
authors.forename: Takashi
authors.initials: T
authors.lastname: Kumazawa
authors.forename: Kiyonori
authors.initials: K
authors.lastname: Yoshii
mesh_terms: D000818:Animals; D002122:Calcium Chloride / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D006982:Hypertonic Solutions; D009994:Osmolar Concentration; D011892:Rana catesbeiana / Q000502:physiology*; D011984:Sensory Receptor Cells / Q000187:drug effects* / Q000502:physiology; D012965:Sodium Chloride / Q000494:pharmacology*; D013395:Sucrose / Q000494:pharmacology; D013649:Taste / Q000187:drug effects* / Q000502:physiology; D014508:Urea / Q000494:pharmacology
chemical_list: D006982:Hypertonic Solutions; D012965:Sodium Chloride; D013395:Sucrose; D014508:Urea; D002122:Calcium Chloride