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.e^bx. 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.