Event Abstract Back to Event RAPID NONGENOMIC EFFECTS OF CORTISOL ON MEMBRANE FLUIDITY AND PHOSPHORYLATION IN RAINBOW TROUT LIVER. Laura Dindia1 and Mathilakath Vijayan1* 1 University of Waterloo, Canada While rapid steroid signaling is thought to play a key role in cellular function, little is known about the nongenomic role of cortisol in hepatic tissue. Therefore, we studied the nongenomic effects of cortisol on the biophysical properties of the liver plasma membrane and investigated the effects on the phosphorylation profile of protein kinase A (PKA), protein kinase C (PKC) and AKT kinase substrate proteins. The effect of cortisol on membrane fluidity was examined by measuring fluorescence anisotropy of the membrane probe 1,6-diphenyl-1,3,5-hexatriene (DPH) in isolated liver plasma membrane fractions. In vitro, physiological (100 ng/ml) and pharmacological (500 and 1000 ng/ml) cortisol concentrations were shown to rapidly increase hepatic membrane fluidity. Moreover, cortisol rapidly induced phosphorylation of several PKC substrate proteins. These results indicate for the first time that stress-induced plasma cortisol levels modulates liver membrane fluidity, which may lead to rapid intracellular signaling in rainbow trout. Acknowledgements This research was supported by Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grant to MMV, and a NSERC Post-graduate Scholarship (PGS D) to LD.