Steroid hormone-induced effects on membrane fluidity and their potential roles in non-genomic mechanisms

Steroid hormones are lipophilic suggesting they intercalate into the bilaye r of target cell plasma membranes, potentially altering the fluidity and fu nction of the membrane. The present study measured the effects of steroidal exposure on both phospholipid fluidity and integral protein mobility. Stud ies were performed on the effects of a variety of steroids on phosphatidylc holine liposomes, synaptosomal plasma membranes and sarcoplasmic reticulum membranes. Progesterone decreased the lipid fluidity, whereas testosterone had no effect on lipid movement. The estrogen, 17 beta-estradiol, an aromat ised metabolite of testosterone, increased lipid mobility. In each case, th e steroid action was concentration-dependent. The steroids all increased th e activity of the Ca2+ ATPase of SR membrane, in keeping with their effects on this enzyme's aggregation state. The results suggest that, although lip id fluidity is a factor influencing protein activity, their mobility within the bilayer is the primary determinant of enzyme activity in the membrane for most proteins. (C) 2000 Elsevier Science Inc. All rights reserved.