Fluidity and Function of Hepatocyte Plasma Membranes

Abstract

LIPID-PROTEIN INTERACTIONS INMEMBRANES This review considers the basic biological problem of how the lipids and proteins of hepatocyte plasma membranes interact to mediate and regulate membrane functions. The following general hypothesis, which is applicable to all natural membranes, is a suitable framework for the discussion, inasmuch as it rests on a considerable body of experimental evidence. MEMBRANE MEMBRANE PROTEINS influence LIPIDS(and the specific -(and their functions properties) mediated by them)The influence of endogenous membrane enzymes, such as phospholipases (1-4), methyltransferases (5, 6), and fatty acid desaturases (7-lo), on membrane phospholipids is well-documented. Such reactions can alter the composition and properties of the bilayer lipid environment and thereby affect the functions of those membrane proteins ("integral" proteins) which are embedded in or traverse the lipid core of the membrane. A key property of the lipids, in this regard, is the "fluidity", or general motional freedom of the lipid molecules. A growing body of evidence indicates that the fluidity of the lipid environment influences the activity of such physiologically important membrane enzymes as the (Na+ + Ka+)-dependent adenosine triphosphatase (11-16) and hormoneresponsive adenylate cyclase (16-20). The fluidity also modulates transmembrane transport processes (21-24) and is a determinant of the passive permeability characteristic of a given bilayer (23, 25-28).The interactions of membrane proteins and lipids implicit in the general hypothesis above could provide regulatory loops for the control of important cell functions. For example, recent evidence indicates that calcium ion

Rat Hepatocytes Transport Water Mainly via a Non-channel-mediated Pathway

“…As expected from the differences in lipid composition, the membrane fluidity of hepatocytes, estimated by measuring steady-state anisotropy, was higher than that of cholangiocytes. Membrane fluidity is recognized to influence transmembrane transport processes, including water movement (32). Thus, these differences in membrane lipid composition and fluidity between hepatocytes and cholangiocytes may help to provide a biophysical explanation for their different mechanisms of water transport; i.e.…”

Up-to-Date Insight About Membrane Remodeling as a Mechanism of Action for Ethanol-Induced Liver Toxicity

“…Any alteration of the optimal range for membrane fluidity has influence on many biological functions such as membrane enzyme and receptor activities, or transmembrane transport processes (Ho et al, 1994;Schachter, 1984;Stubbs et al, 1988). Furthermore, more recently, it was also shown its fundamental role in cell signalling responses to xenobiotic stress (polycyclic aromatic hydrocarbons, cisplatin or ethanol), leading to cell death such as apoptosis (Rebillard et al, 2007;Sergent et al, 2005;Tekpli et al, 2011).…”

Membranes and the Clinician

“…Over the past l S years o r so it has become increasingly clear that membrane lipids and their properties can influence membrane proteins and their specific functions and visa versa (3) Several recent reviews (3-5) have dealt with membrane lipid fluidit y a nd its measurement in hepatic and intestinal plasma membranes, so this article couches only o n certain key aspects of this topic and the reader is referred to rhe above reviews for further details. The fluidity of biological and model membranes has clearly been shown to depend upon a number of membrane compositional parameters including: lipid:prmein (w:w) ratio; cholesterol: phospholipid (mol:mol) ratio; sphingomyclin:lccithin (mol:mol) ratio; and rh e length and degree of unsaruration of phospholipid fatty acy l chains (3).…”

“…The fluidity of biological and model membranes has clearly been shown to depend upon a number of membrane compositional parameters including: lipid:prmein (w:w) ratio; cholesterol: phospholipid (mol:mol) ratio; sphingomyclin:lccithin (mol:mol) ratio; and rh e length and degree of unsaruration of phospholipid fatty acy l chains (3). Any study on membrane fluidity should not only measure fluidity per sc bur also examine each of these compositional parameters.…”

“…For example, alterations in small and large intestinal plasma membrane fluidity have been shown to influence certain enzyme activities such as adenylatc and guanylate cyclase, alkaline phosphatase Na+ -K+ -dependent ATPasc, and ca2 + -dependent ATPase as well as a+ -dependent glucose transport, Na+ / H + exchange and water permeability (5). Alterations in hepatic p lasma me~branc lipid composition and/or fluidity have also been sh own to influence bile sa lt dependent and independent bile flow as well as Na+ -K + -ATPase activity (3,4). Furthermore, ch is laboratory (5) has rece ntly demonstrated that dierary lipids, luminal calcium io n co ncentrations, th e norm al physiological processes of ageing and differentiation, as well as the administration of carcinogens, estrogen, vitamin D, glucocorticoids and insulin may influence the lipid ..:omposici on and fluidity of intestinal plasma membranes whic h, in tu rn, modu lates a number of their important protein-mediated activities.…”