title: Modulation of lipid fluidity of small- and large-intestinal antipodal membranes by Ca2+.
abstract: A series of experiments were conducted to examine the role of Ca2+ in modulating the fluidity of rat small- and large-intestinal antipodal plasma membranes and their liposomes. This bivalent cation was found to decrease the fluidity of these preparations in a complex manner involving at least two distinct mechanisms. The first appeared to be a direct effect of Ca2+ on fluidity, was readily reversible by addition of EGTA and presumably involved binding of Ca2+ to anionic sites in the lipid bilayers of these membranes. This effect was seen with all preparations examined. In contrast, the second effect of Ca2+ on fluidity was only seen in intact small-intestinal brush-border membranes, appeared to be indirect, was time- and cation-dependent, was only minimally reversible by addition of EGTA, and appeared to involve stimulation of membrane-bound enzymes which altered this membrane's fatty acid composition. Furthermore, regional differences in this latter effect of Ca2+ on brush-border membrane fluidity were also seen in these studies, i.e. proximal greater than distal small intestine.
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002413:Cations, Divalent / Q000494:pharmacology; D004161:Diphenylhexatriene; D004533:Egtazic Acid / Q000494:pharmacology; D005454:Fluorescence Polarization; D007413:Intestinal Mucosa / Q000378:metabolism*; D007422:Intestines / Q000187:drug effects; D008081:Liposomes / Q000378:metabolism; D008297:Male; D008560:Membrane Fluidity / Q000187:drug effects*; D008563:Membrane Lipids / Q000378:metabolism*; D008871:Microvilli / Q000187:drug effects / Q000378:metabolism; D051381:Rats
chemical_list: D002413:Cations, Divalent; D008081:Liposomes; D008563:Membrane Lipids; D004161:Diphenylhexatriene; D004533:Egtazic Acid; D002118:Calcium