D-myo-inositol derivatives alter liposomal membrane fluidity.

We investigated the effect on membrane fluidity induced by D-myo-inositol derivatives (IP3, IP4, IP5, IP6). Fluidity was determined as the anisotropy of fluorescence polarisation from liposome model membranes labelled with DPH (1,6-diphenyl-1,3,5 hexatriene). IP3 (10(-10) to 10(-5) M) increased the membrane fluidity with a maximum effect at 10(-5) M. For IP4, IP5 and IP6, at concentrations less than 10(-6) M these derivatives increased the membrane viscosity (i.e. reduced fluidity). This effect was enhanced when the derivatives were incorporated in the vesicles, rather than added to the vesicle suspension. In this case IP5 and IP6 increased viscosity over the reference values. We conclude that inositol derivatives directly modified membrane fluidity which could play a role in their effects in biological systems, beside the one mediated by binding to specific receptors.