Cortisol effect on (Na+ + K+)-stimulated ATPase activity and on bilayer fluidity of dog brain synaptosomal plasma membranes.

The binding of [14C]cortisol into dog brain synaptosomal plasma membranes (SPM) follows an exponential path described by the general formula y = a.ebx. The specific activity of the SPM-bound (Na+ + K+)-stimulated ATPase was linearly increased at different concentrations of cortisol. Changes in the allosteric properties of (Na+ + K+)-stimulated ATPase by fluoride (F-) (i.e. changes of Hill coefficients) indicate that cortisol increases the membrane fluidity. The fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene-labeled SPM decreased in cortisol treated SPM compared to untreated (control) SPM, which is consistent with a general increase in membrane fluidity. This increase of fluidity by cortisol may play a role in the physiological effects of this hormone in the brain.