SIGNAL-TRANSDUCTION FOR TAUROCHOLIC ACID IN THE OLFACTORY SYSTEM OF ATLANTIC SALMON

Conjugated bile acids such as taurocholic acid (TChA) are potent olfac tory stimuli for Atlantic salmon (Salmo salar). A plasma membrane rich fraction was derived from salmon olfactory rosettes and used to inves tigate TChA signal transduction and receptor binding. In the presence of GTP gamma S, TChA caused dose-dependent stimulation of phosphatidyl inositol 4,5-bisphosphate (PIP2) breakdown, half maximal at less than 10(-7) M TChA. Stimulation of PIP2 breakdown by TChA required GTP gamm a S, was blocked by GDP beta S, and was mimicked by AlF4-, consistent with a G protein requirement. AlF4- and Ca2+ stimulated breakdown of P IP2, but not phosphatidylcholine, arguing against a non-specific lipas e activation. Stimulation of PIP2 breakdown by TChA was maximal at low Ca2+ concentration, less than or equal to 10 nM. Conventional binding analysis with H-3-TChA was inconclusive due to a high degree of non-s pecific binding and to lack of tissue specificity expected for an olfa ctory receptor. Analysis of odorant amino acid binding indicated possi ble interaction of TChA with a putative acidic amino acid receptor but no interaction of TChA with a putative neutral amino acid receptor. W e conclude that olfactory discrimination between amino acids and bile acids occurs in part at the receptor level while both classes of odors appear to use the same signal transduction mechanism, G protein media ted activation of phosphoinositide specific phospholipase C (PLC).