title: Membrane Lipid Microenvironment Modulates Thermodynamic Properties of the Na+-K+-ATPase in Branchial and Intestinal Epithelia in Euryhaline FishIn vivo.
abstract: We have analyzed the effects of different native membrane lipid composition on the thermodynamic properties of the Na+-K+-ATPase in different epithelia from the gilthead seabreamSparus aurata. Thermodynamic parameters of activation for the Na+-K+-ATPase, as well as contents of lipid classes and fatty acids from polar lipids were determined for gill epithelia and enterocytes isolated from pyloric caeca, anterior intestine and posterior intestine. Arrhenius analyses of control animals revealed differences in thermal discontinuity values (Td) and activation energies determined at both sides ofTdbetween intestinal and gill epithelia. Eyring plots disclosed important differences in enthalpy of activation (ΔH‡) and entropy of activation (ΔS‡) between enterocytes and branchial cells. Induction of n-3 LCPUFA deficiency dramatically altered membrane lipid composition in enterocytes, being the most dramatic changes the increase in 18:1n-9 (oleic acid) and the reduction of n-3 LCPUFA (mainly DHA, docosahexaenoic acid). Strikingly, branchial cells were much more resistant to diet-induced lipid alterations than enterocytes, indicating the existence of potent lipostatic mechanisms preserving membrane lipid matrix in gill epithelia. Paralleling lipid alterations, values ofEa1, ΔH‡and ΔS‡for the Na+-K+-ATPase were all increased, whileTdvalues vanished, in LCPUFA deficient enterocytes. In turn, Differences in thermodynamic parameters were highly correlated with specific changes in fatty acids, but not with individual lipid classes including cholesterolin vivo. Thus,Tdwas positively related to 18:1n-9 and negatively to DHA.Td, Ea1and ΔH‡were exponentially related to DHA/18:1n-9 ratio. The exponential nature of these relationships highlights the strong impact of subtle changes in the contents of oleic acid and DHA in setting the thermodynamic properties of epithelial Na+-K+-ATPasein vivo. The effects are consistent with physical effects on the lipid membrane surrounding the enzyme as well as with direct interactions with the Na+-K+-ATPase.
authors.affiliation: Laboratorio de Fisiología Animal, Sección Biología, Departamento de Biología Animal, Facultad de Ciencias, Edafología y Geología, Universidad de La Laguna Tenerife, Spain.
authors.forename: Mario
authors.initials: M
authors.lastname: Díaz
authors.affiliation: Laboratorio de Fisiología Animal, Sección Biología, Departamento de Biología Animal, Facultad de Ciencias, Edafología y Geología, Universidad de La Laguna Tenerife, Spain.
authors.forename: Rosa
authors.initials: R
authors.lastname: Dópido
authors.affiliation: Laboratorio de Fisiología Animal, Sección Biología, Departamento de Biología Animal, Facultad de Ciencias, Edafología y Geología, Universidad de La Laguna Tenerife, Spain.
authors.forename: Tomás
authors.initials: T
authors.lastname: Gómez
authors.affiliation: Laboratorio de Fisiología Animal, Sección Biología, Departamento de Biología Animal, Facultad de Ciencias, Edafología y Geología, Universidad de La Laguna Tenerife, Spain.
authors.forename: Covadonga
authors.initials: C
authors.lastname: Rodríguez
keywords: DHA (docosahexaenoic acid); activation energy (Ea); enthalpy of activation (ΔS‡); entropy of activation (ΔH‡); epithelial Na+-K+-ATPase; membrane lipid microenvironment; n-3 long chain polyunsaturated fatty acids (LCPUFA); oleic acid