Ca2+ extrusion across plasma membrane and Ca2+ uptake by intracellular stores.

MgATP-dependent glucose 6-phosphate-stimulated Ca2+ accumulation in liver microsomal fractions. Effects of inositol 1,4,5-trisphosphate and GTP.

The effect of dietary essential fatty acid (EFA) deficiency on lipid composition, fluidity and important enzyme and transport activities of liver microsomal membrane was studied in weanling rats. After 133 d of EFA deficiency, no difference was noticed in membrane phospholipid, cholesterol and protein levels, but a significant change occurred in the fatty acid composition of bilayer phospholipids. In EFA-deficient rats, linoleic (18:2(n-6] and arachidonic (20:4(n-6] acids were both severely lower while oleic (18:1(n-9], palmitoleic (16:1(n-7] and particularly 5,8,11-eicosatrienoic (20:3(n-9] acids were significantly higher than in controls. The higher level of the latter tended to compensate for the lower level of 20:4(n-6). Membrane fluidity, as estimated by the reciprocal of the order parameter S, was lower in the deficient rats than in the controls, and all the measured microsomal enzyme activities were markedly affected. NADH-Cyt b5 electron transferring system, coupled with the fatty acid desaturation system, was higher than in controls. In contrast, the cytochrome P450 complex activity was lower and some of the important liver detoxifying enzyme activities were lower due to physical-chemical changes in the microsomal membrane. Calcium uptake and Ca2+-ATPase activity were also significantly lower in EFA-deficient rats than in controls. It was concluded that fatty acid composition may be the major factor contributing to membrane fluidity and function and that EFA might play a role in regulating the intrinsic membrane protein activities.

The effect of dietary essential fatty acid deficiency on the composition and properties of the liver microsomal membrane of rats.

The effect of dietaryessential fattyacid(EFA) deficiency on lipid composition, fluidityand importanten zyme and transport activities of liver microsomal mem brane was studied in weanling rats. After 133 d of EFA deficiency, no difference was noticed in membrane phos- pholipid, cholesterol and protein levels, but a significant change occurred in the fatty acid composition of bilayer phospholipids. In EFA-deficientrats, linoleic (18:2(n-6)) and arachidonic(20:4(n-6)) acids wereboth severelylower while oleic (18:l(n-9)), palmitoleic (16:l(n-7)) and par ticularly5,8,11-eicosatrienoic (20:3(n-9)> acids were sig nificantlyhigher than in controls. The higher level of the latter tended to compensate for the lowerlevel of 20:4(n- 6). Membranefluidity,as estimated bythe reciprocalof the order parameter S, was lower in the deficient rats than in the controls, and all the measured microsomal enzyme activities were markedly affected. NADH-Cytb5 electron transferringsystem, coupled with the fatty acid desatura- tion system, was higher than in controls. In contrast, the cytochrome P4M) complex activitywas lower and some of the importantliverdetoxifyingenzyme activitieswere lower due to physical-chemicalchanges inthe microsomal mem brane. Calciumuptake and Ca2+-ATPaseactivitywere also significantlylower in EFA-deficientrats than in controls. Itwas concluded that fattyacid composition may be the majorfactor contributingto membranefluidityand function and that EFA might play a role in regulating the intrinsic membrane proteinactivities. J. liutr. 118:1311-1318, 1988.

The Effect of Dietary Essential Fatty Acid Deficiency on the Composition and Properties of the Liver Microsomal Membrane of Rats RAYMOND CHRISTON,1 YVETTE FERNANDEZ.f CLAÃœDIE CAMBON-GROS.f ALAIN

1. By using Ca-EGTA buffers, the Km for Ca2+ uptake into rat liver heavy microsomes (microsomal fraction) was found to be 0.2 microM free Ca2+. 2. In the absence of oxalate, these vesicles accumulate about 20 nmol of Ca2+/mg of protein. Efflux of Ca2+ from the vesicles is much faster at pH 7.6 than at pH 6.8, but does not apparently show saturation kinetics or any stringent requirement for external ions. 3. The steady-state distribution of Ca2+ between the microsomes and the medium in the presence of ATP and the absence of oxalate is dependent on Ca2+ load. When the vesicles are loaded to 50% capacity, the external free Ca2+ concentration is 70 nM. 4. The affinity of heavy microsomes for Ca2+ is such that is seems likely that they has a dominant role in the determination of cytoplasmic free Ca2+ concentrations.

Kinetic properties of the Ca2+-accumulation system of a rat liver microsomal fraction

Characterization of the hormone-sensitive Ca2+ uptake activity of the hepatic endoplasmic reticulum

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Characterization of the hormone-sensitive Ca2+ uptake activity of the hepatic endoplasmic reticulum