[Membrane fluidity--biophysical parameter in relation to membrane transport processes].

Membrane fluidity is a complex parameter, influenced both through some biophysical (temperature, electrical charges, pH) and biochemical factors (protein/phospholipids ratio, phospholipids/cholesterol ratio, degree of fatty acids unsaturation). It is a parameter that reflects the main membrane characteristic organization (gel or liquid crystal structure). Experiments provide consistent data about membrane fluidity relations to various cellular processes, especially membrane processes. Passive transport is influenced directly by membrane lipid composition, and consequently, membrane fluidity, or by channels and carriers molecules interactions with adjacent membrane lipids. Membrane diffusion is related both to the hydrophobic nature of the particles and of the membrane environment. Depending on the mode of interaction with membrane proteins, lipids may be classified as non-annular lipids, annular and "mass" lipids. Different types of fatty acids affect the function of many channels, by stimulating or inhibiting them. These effects might be mediated through direct binding of the lipids to the channel or through indirect hydrophobic interactions. Active transport pumps conformation could be modulated, also, through interactions with adjacent lipids of the bilayer (especially cholesterol) and membrane micro-domains organization. In conclusion, membrane fluidity is close related both to passive and active transport.