title: Transduction mechanism(s) of Na-saccharin in the blowfly Protophormia terraenovae: evidence for potassium and calcium conductance involvement.
abstract: The study on transduction mechanisms underlying bitter stimuli is a particularly intriguing challenge for taste researchers. The present study investigates, in the labellar chemosensilla of the blowfly Protophormia terraenovae, the transduction mechanism by which saccharin evokes the response of the "deterrent" cell, with particular attention to the contribution of K(+) and Ca(2+) current and the role of cyclic nucleotides, since second messengers modulate Ca(2+), Cl(-) and K(+) currents to different extents. As assessed by extracellular single-sensillum recordings, our results show that the addition of a Ca(2+) chelator such as EGTA or the Ca(2+) current blockers SK&F-96365, Mibefradil, Nifedipine and W-7 decrease the response of the "deterrent" cell to saccharin. A similar decreasing effect was also obtained following the addition of 4-aminopyridine, a K(+) current blocker. On the contrary, the membrane-permeable cyclic nucleotide 8-bromoguanosine 3',5'-cyclic monophosphate (8Br-cGMP) activates this cell and shows an additive effect when presented mixed with saccharin. Our results are consistent with the hypothesis that in the labellar chemosensilla of the blowfly both Ca(2+) and K(+) ions are involved in the transduction mechanism of the "deterrent" cell in response to saccharin. Our results also suggest a possible pathway common to saccharin and 8Br-cGMP.
authors.affiliation: Department of Experimental Biology, Section of General Physiology, University of Cagliari, Cittadella Universitaria di Monserrato, 09042 Monserrato, CA, Italy.
authors.forename: Carla
authors.initials: C
authors.lastname: Masala
authors.forename: Paolo
authors.initials: P
authors.lastname: Solari
authors.forename: Giorgia
authors.initials: G
authors.lastname: Sollai
authors.forename: Roberto
authors.initials: R
authors.lastname: Crnjar
authors.forename: Anna
authors.initials: A
authors.lastname: Liscia
mesh_terms: D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology; D002628:Chemoreceptor Cells / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D006152:Cyclic GMP / Q000031:analogs & derivatives / Q000494:pharmacology; D004175:Diptera / Q000166:cytology / Q000502:physiology*; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D009055:Mouth / Q000166:cytology / Q000502:physiology*; D026902:Potassium Channel Blockers / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology; D012439:Saccharin / Q000494:pharmacology; D011984:Sensory Receptor Cells / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D012964:Sodium / Q000494:pharmacology; D013649:Taste / Q000187:drug effects / Q000502:physiology*
chemical_list: D002121:Calcium Channel Blockers; D015220:Calcium Channels; D007473:Ion Channels; D026902:Potassium Channel Blockers; D015221:Potassium Channels; C016276:8-bromocyclic GMP; D012964:Sodium; D012439:Saccharin; D006152:Cyclic GMP