RAPID KINETIC MEASUREMENTS OF 2ND MESSENGER FORMATION IN OLFACTORY CILIA FROM CHANNEL CATFISH

The effect of stimulating olfactory cilia from the channel catfish (Ic talurus punctatus) with odorant amino acids on the formation of adenos ine 3',5'-cyclic monophosphate, guanosine 3',5'-cyclic monophosphate, and inositol 1,4,5-trisphosphate (IP30 was studied in the subsecond ti me scale using a quenched flow technique. L-Alanine (L-Ala) and L-cyst eine (L-CYS) (100 muM) elicited a transient elevation in IP3 levels th at peaked at 25 ms. In contrast, even at high concentration a mixture of odorant amino acids (1 MM L-Ala, L-CYS, L-norleucine, L-glutamate, L-proline, and L-arginine) did not elicit a change in cAMP levels in t his time scale and caused only relatively slow and minor increases in cGMP. The dose-response relationship for the IP3 response of L-Cys and L-Ala in the range from 10 nM to 1 mM is consistent with previous ele ctrophysiological and ligand binding experiments. Odorant amino acid-s timulated IP, formation was GTP dependent and was inhibited by guanosi ne 5'-O-(2-thiodiphosphate), suggesting that the response was G protei n mediated. These results are consistent with a mediatory role for IP3 in amino acid olfactory signal transduction in catfish.