Recent issues of Hepatology have presented several articles dealing with the fluidity of membranes from liver cells. Because of continuing interest in this area of membrane biology, we elected to prepare a brief review of this complex area. An excellent and detailed review of membrane fluidity and hepatic function was published in this journal 2 years ago ( 1 ).
Our first task is to explain what is meant by membrane fluidity. In this context, "fluidity" does not have a precise definition and is usually taken to mean the relative motional freedom of membrane constituents, particularly lipids. In a more rigorous sense, fluidity consists of rotational diffusion, which is related to microviscosity and hindered anisotropic rotations, which are related to lipid order (2, 3). The most widely used technique for measurement of membrane physical properties is fluorescence polarization of probe molecules inserted into membranes. This editorial will discuss how fluorescence measurements can be used to distinguish between these two properties, microviscosity and lipid order, and the possible significance of changes in fluidity to membrane function.
This study was supported by the Veterans Administration and USPHS Grants AA06399. AA03527 (Alcohol Research Center).