Membrane lipid fluidity and its effect on the activation energy of membrane-associated enzymes

Membrane-Mediated Allosteric Action of Serotonin on a Noncognate G-Protein-Coupled Receptor

The structure and dynamics of the lipid membrane can affect the activity of membrane proteins. Therefore, small lipophilic molecules that alter membrane properties (such as the neurotransmitter serotonin) can potentially modulate receptor activity without binding to the receptor. Here, we investigated how the activity of neuropeptide Y type 4 receptor (Y4R, reconstituted in lipid bicelles) is modulated by serotonin, which has no known interaction with Y4R. We found a serotonin-concentration-dependent decrease (down to 0.1 mM of serotonin) in the ligand affinity of Y4R. This effect correlates with a serotonin-induced reduction of the resistance of the bilayer to indentation (measured by atomic force microscopy) and bilayer thickness (measured by solid state NMR) in two different types of zwitterionic lipid bicelles. Our findings indicate a "membrane-mediated allosteric effect" of serotonin on the activation of Y4R and suggest the potential for developing pharmacophores, which can modulate cellular signaling without directly interacting with any receptor.

Understanding differential aspects of microdiffusion (channeling) in the Coenzyme Q and Cytochrome c regions of the mitochondrial respiratory system

Over the past decades, models of the organization of mitochondrial respiratory system have been controversial. The goal of this perspective is to assess this "conflict of models" by focusing on specific kinetic evidence in the two distinct segments of Coenzyme Q- and Cytochrome c-mediated electron transfer. Respiratory supercomplexes provide kinetic advantage by allowing a restricted diffusion of Coenzyme Q and Cytochrome c, and short-range interaction with their partner enzymes. In particular, electron transfer from NADH is compartmentalized by channeling of Coenzyme Q within supercomplexes, whereas succinate oxidation proceeds separately using the free Coenzyme Q pool. Previous evidence favoring Coenzyme Q random diffusion in the NADH-dependent electron transfer is due to downstream flux interference and misinterpretation of results. Indeed, electron transfer by complexes III and IV via Cytochrome c is less strictly dependent on substrate channeling in mammalian mitochondria. We briefly describe these differences and their physiological implications.

Origin of the nonlinear structural and mechanical properties in oppositely curved lipid mixtures

Structural and mechanical properties of membranes such as thickness, tail order, bending modulus and curvature energetics play crucial role in controlling various cellular functions that depend on the local lipid organization and membrane reshaping. While behavior of these biophysical properties are well understood in single component membranes, very little is known about how do they change in the mixed lipid membranes. Often various properties of the mixed lipid bilayers are assumed to change linearly with the mole fractions of the constituent lipids which, however, is true for "ideal" mixing only. In this study, using molecular dynamics simulations, we show that structural and mechanical properties of binary lipid mixture change nonlinearly with the lipid mole fractions, and the strength of the nonlinearity depends on two factors - spontaneous curvature difference and locally inhomogeneous interactions between the lipid components.

Membrane Phenotypic, Metabolic and Genotypic Adaptations of Streptococcus oralis Strains Destined to Rapidly Develop Stable, High-Level Daptomycin Resistance during Daptomycin Exposures

The Streptococcus mitis-oralis subgroup of viridans group streptococci are important human pathogens. We previously showed that a substantial portion of S. mitis-oralis strains (>25%) are 'destined' to develop rapid, high-level, and stable daptomycin (DAP) resistance (DAP-R) during DAP exposures in vitro. Such DAP-R is often accompanied by perturbations in distinct membrane phenotypes and metabolic pathways. The current study evaluated two S. oralis bloodstream isolates, 73 and 205. Strain 73 developed stable, high-level DAP-R (minimum inhibitory concentration [MIC] > 256 µg/mL) within 2 days of in vitro DAP passage ("high level" DAP-R [HLDR]). In contrast, strain 205 evolved low-level and unstable DAP-R (MIC = 8 µg/mL) under the same exposure conditions in vitro ("non-HLDR"). Comparing the parental 73 vs. 73-D2 (HLDR) strain-pair, we observed the 73-D2 had the following major differences: (i) altered cell membrane (CM) phospholipid profiles, featuring the disappearance of phosphatidylglycerol (PG) and cardiolipin (CL), with accumulation of the PG-CL pathway precursor, phosphatidic acid (PA); (ii) enhanced CM fluidity; (iii) increased DAP surface binding; (iv) reduced growth rates; (v) decreased glucose utilization and lactate accumulation; and (vi) increased enzymatic activity within the glycolytic (i.e., lactate dehydrogenase [LDH]) and lipid biosynthetic (glycerol-3-phosphate dehydrogenase [GPDH]) pathways. In contrast, the 205 (non-HLDR) strain-pair did not show these same phenotypic or metabolic changes over the 2-day DAP exposure. WGS analyses confirmed the presence of mutations in genes involved in the above glycolytic and phospholipid biosynthetic pathways in the 73-D2 passage variant. These data suggest that S. oralis strains which are 'destined' to rapidly develop HLDR do so via a conserved cadre of genotypic, membrane phenotypic, and metabolic adaptations.

Mitochondrial membranes in cardiac muscle from Antarctic notothenioid fishes vary in phospholipid composition and membrane fluidity

Antarctic notothenioid fishes are highly stenothermal, yet their tolerance for warming is species-dependent. Because a body of literature points to the loss of cardiac function as underlying thermal limits in ectothermic animals, we investigated potential relationships among properties of ventricular mitochondrial membranes in notothenioids with known differences in both cardiac mitochondrial metabolism and organismal thermal tolerance. Fluidity of mitochondrial membranes was quantified by fluorescence depolarization for the white-blooded Chaenocephalus aceratus and the red-blooded Notothenia coriiceps. In these same membranes, lipid compositions and products of lipid peroxidation, the latter of which can disrupt membrane order, were analyzed in both species and in a second icefish, Pseudochaenichthys georgianus. Mitochondrial membranes from C. aceratus were significantly more fluid than those of the more thermotolerant species N. coriiceps (P < .0001). Consistent with this, ratios of total phosphatidylethanolamine (PE) to total phosphatidylcholine (PC) were lower in membranes from both species of icefishes, compared to those of N. coriiceps (P < .05). However, membranes of N. coriiceps displayed a greater unsaturation index (P < .0001). No differences among species were found in membrane products of lipid peroxidation. With rising temperatures, greater contents of PC in mitochondrial membranes from ventricles of icefishes are likely to promote membrane hyperfluidization at a lower temperature than for cardiac mitochondrial membranes from the red-blooded notothenioid. We propose that physical and chemical properties of the mitochondrial membranes may contribute to some of the observed differences in thermal sensitivity of physiological function among these species.

Association of Delta-6-Desaturase Expression with Aggressiveness of Cancer, Diabetes Mellitus, and Multiple Sclerosis: A Narrative Review

Background: The phosphatidylinositol 3-kinase/ protein kinase B /mammalian target of rapamycin (PI3K/Akt/ mTOR) signaling regulates multiple cellular processes and organizes cell proliferation, survival, and differentiation with the available nutrients, in particular, fatty acids. Polyunsaturated fatty acids (PUFAs) are cytotoxic to cancer cells and play a critical role in the treatment of multiple sclerosis (MS) and diabetes mellitus (DM). PUFAs are produced in the body by desaturases and elongases from dietary essential fatty acids (EFAs), primarily involving delta-6-desaturase (D6D). D6D is a rate-limiting enzyme for maintaining many aspects of lipid homeostasis and normal health. D6D is important to recognize the mechanisms that regulate the expression of this enzyme in humans. A lower level of D6D was seen in breast tumors compared to normal tissues. Interestingly, the elevated serum level of D6D was seen in MS and DM, which explains the critical role of D6D in inflammatory diseases. Methods: We searched databases of PubMed, Web of Science (WOS), Google Scholar, Scopus and related studies by predefined eligibility criteria. We assessed their quality and extracted data. Results: Regarding the mTOR signaling pathway, there is remarkable contributions of many inflammatory diseases to attention to common metabolic pathways are depicted. Of course, we need to have the insights into each disorder and their pathological process. The first step in balancing the intake of EFAs is to prevent the disruption of metabolism and expression of the D6D enzyme. Conclusions: The ω6 and ω3 pathways are two major pathways in the biosynthesis of PUFAs. In both of these, D6D is a vital bifunctional enzyme desaturating linoleic acid or alpha-linolenic acid. Therefore, if ω6 and ω3 EFAs are given together in a ratio of 2: 1, the D6D expression will be down-regulated and normalized.

Molecular Understanding of Aβ-hIAPP Cross-Seeding Assemblies on Lipid Membranes

Amyloid-β (Aβ) and human islet polypeptide (hIAPP) are the causative agents responsible for Alzheimer's disease (AD) and type II diabetes (T2D), respectively. While numerous studies have reported the cross-seeding behavior of Aβ and hIAPP in solution, little effort has been made to examine the cross-seeding of Aβ and hIAPP in the presence of cell membranes, which is more biologically relevant to the pathological link between AD and T2D. In this work, we computationally study the cross-seeding and adsorption behaviors of Aβ and hIAPP on zwitterionic POPC and anionic 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC)/1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylglycerol (POPG) mixed bilayers using all-atom molecular dynamics (MD) simulations, particularly aiming to the effects of the initial orientation of the Aβ-hIAPP assembly and the lipid composition of cell membranes on mutual structural and interaction changes in both Aβ-hIAPP assembly and lipid bilayers at the atomic level. Aβ-hIAPP cross-seeding assembly always preferred to adopt a specific orientation and interface to associate with both lipid bilayers strongly via the N-terminal strands of Aβ. Such membrane-bound orientation explains experimental observation that hybrid Aβ-hIAPP fibrils on cell membranes showed similar morphologies to pure hIAPP fibrils. Moreover, Aβ-hIAPP assembly, regardless of its initial orientations, interacted more strongly with POPC/POPG bilayer than POPC bilayer, indicating that electrostatic interactions are the major forces governing peptide-lipid interactions. Strong electrostatic interactions were also attributed to the formation of Ca²⁺ bridges connecting both negatively charged Glu of Aβ and PO₄ head groups of lipids, which facilitate the association of Aβ-hIAPP with the POPC/POPG bilayer. It was also found that the strong peptide-lipid binding reduced lipid fluidity. Both facts imply that Aβ-hIAPP assembly may induce cell damage by altering calcium homeostasis and cell membrane phase. This work provides a better fundamental understanding of cross-seeding of Aβ and hIAPP on cell membranes and a potential pathological link between AD and T2D.

Redox State of Cytochromes in Frozen Yeast Cells Probed by Resonance Raman Spectroscopy

Cryopreservation is a well-established technique used for the long-term storage of biological materials whose biological activity is effectively stopped under low temperatures (suspended animation). Since most biological methods do not work in a low-temperature frozen environment, the mechanism and details of the depression of cellular activity in the frozen state remain largely uncharacterized. In this work, we propose, to our knowledge, a new approach to study the downregulation of the redox activity of cytochromes b and c in freezing yeast cells in a contactless, label-free manner. Our approach is based on cytochrome photobleaching effects observed in the resonance Raman spectra of live cells. Photoinduced and native redox reactions that contributed to the photobleaching rate were studied over a wide temperature range (from -173 to +25 °C). We found that ice formation influences both the rate of cytochrome redox reactions and the balance between the reduced and oxidized cytochromes. We demonstrate that the temperature dependence of native redox reaction rates can be well described by the thermal activation law with an apparent energy of 32.5 kJ/mol, showing that the redox reaction rate is ∼10(15) times slower at liquid nitrogen temperature than at room temperature.

Effect of Temperature and pH on the Esterase Activity of Bile-Salt-Stimulated Human Milk Lipase

The initial rate constants of hydrolysis of 4-nitrophenyl acetate, catalyzed by bile-salt-stimulated human milk lipase, have been measured over the tempera ture range 20 ° C to 37 ° C, in 0.1 M buffer solutions in the pH range 6-10, and in the presence of 2 mM sodium taurocholate. From these data, the values of the energy of activation have been calculated and found to be independent of pH. Analysis of the data has also led to determination of the values of the disso ciation constants, pK1 (8.20) and pK2 (8.70) (at 25°C), and heats of formation, Δ H° (40.2 and 59.4 kJ mol -1, respectively), of the essential ionizable residues of the enzyme.

Effect of Temperature on the Uptake of 35S(-II) by Wine Yeasts

The rates of uptake of 35S from S(-II) solutions by wine yeasts, Saccharomyces cerevisiae strains R92 and R104 and Saccharomyces chevalieri strain R93, were measured at pH 3.1 and 7.2 over the temperature range 5 ° C to 80 ° C and at 0.3 (or 0.5) mM and 5.0 mM S(-II) concentrations. Three critical temperatures were observed; the first, at ca 20 ° C is attributed to a phase change of the yeast cell membrane from a crystalline to a liquid crystalline state; the second, at the temperature of maximum activity at 30 ° C to 40 ° C is thought to arise from a switch from a metastable to a thermodynamically more stable state which is less effective in supporting the transport functions; and the third, at tempera tures greater than 50 ° C correlates well with the thermal viability of the yeasts. Variation of the activation energy, Ea, with extracellular S(-II) concen tration was observed and Ea for the uptake of S(-II) from a solution of 5 mM S(-II) at pH 7.2 was higher than at pH 3.1. The values of Ea support the postulate of a simple diffusion of H2S(aq) and carrier mediated transport of HS-(aq) for the transport of S(-II).

Dietary Fatty Acids and Temperature Modulate Mitochondrial Function and Longevity in Drosophila

Fluctuations in temperature and resource availability are conditions many organisms contend with in nature. Specific dietary nutrients such as fatty acids play an essential role in reproduction, cold adaptation, and metabolism in a variety of organisms. The present study characterizes how temperature and diet interact to modulate Drosophila physiology and life span. Flies were raised on media containing specific saturated, monounsaturated, or polyunsaturated fatty acids supplements at low concentrations and were placed in varied thermal environments. We found that dietary long-chain polyunsaturated fatty acids improve chill coma recovery and modulate mitochondrial function. Additionally, monounsaturated and polyunsaturated fatty acid food supplements were detrimental to life span regardless of temperature, and antioxidants were able to partially rescue this effect. This study provides insight into environmental modulation of Drosophila physiology and life span.

Interplay between ultrastructural findings and atherothrombotic complications in type 2 diabetes mellitus

Accelerated atherosclerosis is the main underlying factor contributing to the high risk of atherothrombotic events in patients with diabetes mellitus and atherothrombotic complications are the main cause of mortality. Like with many bodily systems, pathology is observed when the normal processes are exaggerated or uncontrolled. This applies to the processes of coagulation and thrombosis as well. In diabetes, in fact, the balance between prothrombotic and fibrinolytic factors is impaired and thus the scale is tipped towards a prothrombotic and hypofibrinolytic milieu, which in association with the vascular changes accompanying plaque formation and ruptures, increases the prevalence of ischaemic events such as angina and myocardial infarction. Apart from traditional, modifiable risk factors for cardiovascular disease like hypertension, smoking, elevated cholesterol; rheological properties, endogenous fibrinolysis and impaired platelet activity are rapidly gaining significance in the pathogenesis of atherosclerosis especially in diabetic subjects. Blood clot formation represents the last step in the athero-thrombotic process, and the structure of the fibrin network has a role in determining predisposition to cardiovascular disease. It is no surprise that just like platelets and fibrin networks, erythrocytes have been shown to play a role in coagulation as well. This is in striking contrast to their traditional physiological role of oxygen transport. In fact, emerging evidence suggests that erythrocytes enhance functional coagulation properties and platelet aggregation. Among the spectrum of haematological abnormalities in diabetes, erythrocyte aggregation and decreased deformability of erythrocytes predominate. More importantly, they are implicated in the pathogenesis of microvascular complications of diabetes. The morphology of platelets, fibrin networks and erythrocytes are thus essential role players in unravelling the pathogenesis of cardiovascular complications in diabetic subjects.

Mitochondrial membrane lipid remodeling in pathophysiology: a new target for diet and therapeutic interventions

Mitochondria are arbiters in the fragile balance between cell life and death. These organelles present an intricate membrane system, with a peculiar lipid composition and displaying transverse as well as lateral asymmetry. Some lipids are synthesized inside mitochondria, while others have to be imported or acquired in the form of precursors. Here, we review different processes, including external interventions (e.g., diet) and a range of biological events (apoptosis, disease and aging), which may result in alterations of mitochondrial membrane lipid content. Cardiolipin, the mitochondria lipid trademark, whose biosynthetic pathway is highly regulated, will deserve special attention in this review. The modulation of mitochondrial membrane lipid composition, especially by diet, as a therapeutic strategy for the treatment of some pathologies will be also addressed.

Dietary fat types differently modulate the activity and expression of mitochondrial carnitine/acylcarnitine translocase in rat liver

The carnitine/acylcarnitine translocase (CACT), an integral protein of the mitochondrial inner membrane, belongs to the carnitine-dependent system of fatty acid transport into mitochondria, where beta-oxidation occurs. CACT exchanges cytosolic acylcarnitine or free carnitine for carnitine in the mitochondrial matrix. The object of this study was to investigate in rat liver the effect, if any, of diets enriched with saturated fatty acids (beef tallow, BT, the control), n-3 polyunsaturated fatty acids (PUFA) (fish oil, FO), n-6 PUFA (safflower oil, SO), and mono-unsaturated fatty acids (MUFA) (olive oil, OO) on the activity and expression of CACT. Translocase exchange rates increased, in parallel with CACT mRNA abundance, upon FO-feeding, whereas OO-dietary treatment induced a decrease in both CACT activity and expression. No changes were observed upon SO-feeding. Nuclear run-on assay revealed that FO-treatment increased the transcriptional rate of CACT mRNA. On the other hand, only in the nuclei of hepatocytes from OO-fed rats splicing of the last intron of CACT pre-mRNA and the rate of formation of the 3'-end were affected. Overall, these findings suggest that compared to the BT-enriched diet, the SO-enriched diet did not influence CACT activity and expression, whereas FO- and OO-feeding alters CACT activity in an opposite fashion, i.e. modulating its expression at transcriptional and post-transcriptional levels, respectively.

Reduced activity and expression of mitochondrial citrate carrier in streptozotocin-induced diabetic rats

Citrate carrier (CiC), an integral protein of the mitochondrial inner membrane, plays an important role in hepatic intermediary metabolism, supplying the cytosol with acetyl-coenzyme A for fatty acid and cholesterol synthesis. Here, the effect of streptozotocin-induced diabetes on CiC activity and expression in rat liver was investigated. The rate of citrate transport was reduced by about 35% in mitochondria from diabetic vs. control rats. Kinetic studies in mitochondria from diabetic rats showed a reduction in maximum velocity and almost unchanged Michaelis-Menten constant of the CiC protein. Mitochondrial phospholipid amount was not significantly affected, whereas an increase in the cholesterol content and in the cholesterol/phospholipid ratio was observed. To thoroughly investigate the mechanism responsible for the reduced CiC activity in the diabetic state, molecular studies were performed. Ribonuclease protection assays and Western blotting analysis indicated that both hepatic CiC mRNA accumulation and protein level decreased similarly to the CiC activity. The reduced mRNA level and the lower content of the mitochondrial CiC protein, might account for the decline of CiC activity in diabetic animals. To discriminate between the role played by hyperglycemia from that of hypoinsulinemia in the reduction of CiC activity and expression, studies were conducted administrating phlorizin or insulin to streptozotocin-diabetic rats. Our data indicated that both insulin and glucose affect CiC activity and expression in diabetic rats, although they act at different regulatory steps.

Biosynthesis and regulation of carotenoids in Dunaliella: progresses and prospects

Natural carotenoids are high in demand in global market owing to their widespread applications in nutrition, medicine, food coloring agent and cosmetic, as well as to the natural and healthy preference of consumers today. Some strains of Dunaliella are well known for their talent of massive beta-carotene accumulation. Content of the high bioavailability stereoisomer of beta-carotene, the 9-cis stereoisomer, is highest in Dunaliella among all the natural carotenoids sources. These valuable algae have been exploited commercially for beta-carotene-rich Dunaliella powder and natural beta-carotene in many countries since 1980s. However, drawbacks of traditional production methods have hampered the worldwide promotion of carotenoids production with Dunaliella. To shake off the dilemma, complete understanding of carotenogenic mechanism is urgent. Carotenogenic mechanism in Dunaliella is described in present paper, including carotenogenic pathway and its regulation. Generally, it seems that carotenogenic pathway in Dunaliella is close to the one of higher plants. It is known that reactive oxygen species (ROS) were involved in signal transduction for gene activation. Induction of ROS is in parallel with the enhanced beta-carotene accumulation in Dunaliella. It is suggested that ROS trigger massive carotenoids accumulation in Dunaliella. It also revealed that relation may exist between enhanced beta-carotene accumulation and lipid metabolism. For the talent of beta-carotene synthesis, it is possible that Dunaliella massively accumulates beta-carotene and other high-value carotenoids by genetic technologies.

Exploitation of Dunaliella for beta-carotene production

Halotolerant microalga Dunaliella, which is exploited for the production of dried biomass or cell extract, is used as a medicinal food. With the advancement in this field in recent years, the production of bio-organic compounds such as beta-carotene is established in many countries. Large-scale production of beta-carotene is controlled by numerous stress factors like high light intensity, high salinity, temperature and availability of nutrients. The state-of-the-art strategies in industries in closed systems under new set of inductive factors will additionally promote the ease of commercial production of beta-carotene. This review mainly focuses on the different methodologies employed recently for the optimum production of beta-carotene from Dunaliella species.

Biomarkers of contaminant exposure: results of a field study with flounder (Platichthys flesus) from the southern Baltic Sea

The results of the present study are based on enzyme biomarker measurements in flounder (Platichthys flesus), a flatfish species that is widely distributed in Baltic coastal waters. The fish were collected from known pollution gradients and from reference areas regarded as relatively free of anthropogenic input. Muscular cholinesterases (ChEs), hepatic glutathione S-transferase (GST), and hepatic ethoxyresorufin-O-deethylase (EROD) activities were measured in each sampled specimen of flounder. Generalized linear models (GLM) were used to analyze the dependence of the enzyme activity on sampling year and area as well as on the biological parameters of the fish. Statistically significant differences in the activities of the measured biomarkers were observed between reference and contaminated sites. ChEs and GST activities differed with gender. The results of this study suggest that the location and year of sampling have a significant impact on the activity of all the measured biomarkers.

Differential effects of coconut oil- and fish oil-enriched diets on tricarboxylate carrier in rat liver mitochondria

The mitochondrial tricarboxylate carrier (TCC) plays an important role in lipogenesis being TCC-responsible for the efflux from the mitochondria to the cytosol of acetyl-CoA, the primer for fatty acid synthesis. In this study, we investigated the effects of two high-fat diets with different fatty acid composition on the hepatic TCC activity. Rats were fed for 3 weeks on a basal diet supplemented with 15% of either coconut oil (CO), abundant in medium-chain saturated fatty acids, or fish oil (FO), rich in n-3 polyunsaturated fatty acids. Mitochondrial fatty acid composition was differently influenced by the dietary treatments, while no appreciable change in phospholipid composition and cholesterol level was observed. Compared with CO, the TCC activity was markedly decreased in liver mitochondria from FO-fed rats; kinetic analysis of the carrier revealed a decrease of the Vmax, with no change of the Km. No difference in the Arrhenius plot between the two groups was observed. Interestingly, the carrier protein level and the corresponding mRNA abundance decreased following FO treatment. These data indicate that FO administration markedly decreased the TCC activity as compared with CO. This effect is most likely due to a reduced gene expression of the carrier protein.

Calcium activation of heart mitochondrial oxidative phosphorylation: rapid kinetics of mVO2, NADH, AND light scattering

Parallel activation of heart mitochondria NADH and ATP production by Ca(2+) has been shown to involve the Ca(2+)-sensitive dehydrogenases and the F(0)F(1)-ATPase. In the current study we hypothesize that the response time of Ca(2+)-activated ATP production is rapid enough to support step changes in myocardial workload ( approximately 100 ms). To test this hypothesis, the rapid kinetics of Ca(2+) activation of mV(O(2)), [NADH], and light scattering were evaluated in isolated porcine heart mitochondria at 37 degrees C using a variety of optical techniques. The addition of Ca(2+) was associated with an initial response time (IRT) of mV(O(2)) that was dose-dependent with a minimum IRT of 0.27 +/- 0.02 s (n = 41) at 535 nm Ca(2+). The IRTs for NADH fluorescence and light scattering in response to Ca(2+) additions were similar to mV(O(2)). The Ca(2+) IRT for mV(O(2)) was significantly shorter than 1.6 mm ADP (2.36 +/- 0.47 s; p < or = 0.001, n = 13), 2.2 mm P(i) (2.32 +/- 0.29, p < or = 0.001, n = 13), or 10 mm creatine (15.6.+/-1.18 s, p < or = 0.001, n = 18) under similar experimental conditions. Calcium effects were inhibited with 8 microm ruthenium red (2.4 +/- 0.31 s; p < or = 0.001, n = 16) and reversed with EGTA (1.6 +/- 0.44; p < or = 0.01, n = 6). Estimates of Ca(2+) uptake into mitochondria using optical Ca(2+) indicators trapped in the matrix revealed a sufficiently rapid uptake to cause the metabolic effects observed. These data are consistent with the notion that extramitochondrial Ca(2+) can modify ATP production, via an increase in matrix Ca(2+) content, rapidly enough to support cardiac work transitions in vivo.

Functional characterization of purified zinc transporter from renal brush border membrane of rat

Major zinc binding protein purified from renal brush border membrane (BBM) (R. Kumar, R. Prasad, Biochim. Biophys. Acta 1419 (1999) 23) was reconstituted into liposomes and its functional characteristics were investigated. Physical incorporation of the major zinc binding protein into the proteoliposomes was checked by SDS-PAGE, which showed a single band on silver staining. The structural integrity of the proteoliposomes was assessed by phase contrast microscopy, which revealed the proteoliposomes as globular structures and intact boundaries. Further structural integrity/leakiness of the proteoliposomes was checked by monitoring efflux of Zn(2+) from the pre-loaded proteoliposomes in the presence of either 2 mM Ca(2+) or Cd(2+) or Zn(2+). It was observed that even after 2 h of the initiation of efflux, 85-95% of Zn(2+) was retained in the proteoliposomes, thereby indicating that proteoliposomes were not leaky and maintained structural integrity during the uptake study. Zinc uptake into the proteoliposomes followed Michaelis-Menten kinetics with affinity constant (K(m)) of 1.03 mM and maximal velocity (V(max)) of 1333 nmol/mg protein per min. The uptake process followed first-order kinetics with a rate constant (k) of 1. 09x10(-3) s(-1). The specificity of zinc transport system was determined by studying the interaction of divalent cations viz. Ca(2+) and Cd(2+) with the zinc uptake. It was observed that Cd(2+) competitively inhibited the zinc uptake process with inhibitory concentration (K(i)) of 2.9 mM. Kinetic analysis of inhibitory effect of Cd(2+) on zinc uptake revealed an increase in K(m) to 1.74 mM without influencing V(max). Zn(2+) uptake into the proteoliposomes was found to be temperature sensitive and Arrhenius plot showed a breakpoint at 27 degrees C. The apparent energies of activation (E(a)) were found to be 7.09 and 2.74 kcal/mol below and above the breakpoint, respectively. The initial velocity of Zn(2+) uptake increased with the increase in outwardly directed proton gradient ([H](i) greater than [H](o)). The Zn(2+) uptake was inhibited by DCCD, thereby suggesting the involvement of -COOH groups in the translocation of Zn(2+) across the lipid bilayer. The ratio of acidic to basic amino acids (1.26) strongly indicates that it is an acidic protein. The cysteine content in this protein was insignificant, which further corroborates the possibility that the acidic amino acids might be prominent candidates for binding to zinc. The findings of the present study confirms that 40 kDa major zinc binding glycoprotein purified from renal BBM is a zinc transporter involved in the influx of Zn(2+) into the epithelial cells of the renal tubular system.

Fatty acid and sterol composition of three phytomonas species

Fatty acid and sterol analysis were performed on Phytomonas serpens and Phytomonas sp. grown in chemically defined and complex medium, and P. françai cultivated in complex medium. The three species of the genus Phytomonas had qualitatively identical fatty acid patterns. Oleic, linoleic, and linolenic were the major unsaturated fatty acids. Miristic and stearic were the major saturated fatty acids. Ergosterol was the only sterol isolated from Phytmonas sp. and P. serpens grown in a sterol-free medium, indicating that it was synthesized de novo. When P. françai that does not grow in defined medium was cultivated in a complex medium, cholesterol was the only sterol detected. The fatty acids and sterol isolated from Phytomonas sp. and P. serpens grown in a chemically defined lipid-free medium indicated that they were able to biosynthesize fatty acids and ergosterol from acetate or from acetate precursors such as glucose or threonine.

Functional activity of blood polymorphonuclear leukocytes as an oxidative stress biomarker in human subjects

In the present work, we studied the role of polymorphonuclear leukocytes (PMN) in aged individuals and coronary heart disease (CHD)-bearing patients, two physiopathological processes associated with overproduction of reactive oxygen species (ROS). The effects of antioxidant supplementation on the functional activity of PMN from CHD patients were also determined. The function of PMNs was evaluated by measuring of phagocytosis, killing activity, and ROS production. Luminol amplified chemiluminescence (CL) was used to estimate ROS production by stimulated PMNs. Total cholesterol and the LDL-cholesterol fraction from CHD patients were found to be higher than those recommended, returning to normal levels after antioxidant therapy. PMN CL of CHD patients was found to be higher than the associated control groups. Antioxidant therapy administrated to CHD patients lead to an increase in the killing activity accompanied by a decrease in PMN CL of these subjects. The study also showed that killing activity of PMN from human subjects over 60 years was significantly lower than the activity measured in younger subjects. PMN CL produced after stimulation was found to be positively correlated with the increasing age of human subjects (r=.946, p < .01).

Calcium metabolism, osteoporosis and essential fatty acids: a review

Essential fatty acid (EFA)-deficient animals develop severe osteoporosis coupled with increased renal and arterial calcification. This picture is similar to that seen in osteoporosis in the elderly, where the loss of bone calcium is associated with ectopic calcification of other tissues, particularly the arteries and the kidneys. Recent mortality studies indicate that the ectopic calcification may be considerably more dangerous than the osteoporosis itself, since the great majority of excess deaths in women with osteoporosis are vascular and unrelated to fractures or other bone abnormalities. EFAs have now been shown to increase calcium absorption from the gut, in part by enhancing the effects of vitamin D, to reduce urinary excretion of calcium, to increase calcium deposition in bone and improve bone strength and to enhance the synthesis of bone collagen. These desirable actions are associated with reduced ectopic calcification. The interaction between EFA and calcium metabolism deserves further investigation since it may offer novel approaches to osteoporosis and also to the ectopic calcification associated with osteoporosis which seems to be responsible for so many deaths.

Lead-induced abnormalities in blood-brain barrier permeability in experimental chronic toxicity

The aim of this paper was to determine whether prolonged drinking of lead acetate-containing water by adult rats, which imitates environmental exposure to lead (Pb), affects some morphological and biochemical properties of rat brain microvessels. We noted a significant increase of lead level in capillaries and synaptosomes obtained from brains of rats under chronic toxicity conditions. Intravenously injected horseradish peroxidase (HRP) was used to evaluate the functional state of the blood-brain barrier (BBB). The results indicate that, systematically administered at low doses, lead induces BBB dysfunction. The changes, revealed in light microscopy and confirmed by electron microscopic studies, are typical for "leaky" microvessels, reported for variety of neuropathological conditions associated with BBB damage. Enhanced pinocytotic activity of the endothelial cells and the opening of interendothelial tight junctions, together with enormous phagocytizing action of the pericytes, are the most characteristic ultrastructural features noted. The presence of specific type of perivascular cells containing droplets of lipids in the cytoplasm, together with changes in phospholipid profile in brain capillaries, suggest that altered lipid composition of membranes may, at least in part, be responsible for changes in observed membrane permeability.

Effect of starvation on the activity of the mitochondrial tricarboxylate carrier

The effect of starvation on the activity of the tricarboxylate carrier has been investigated in intact rat liver mitochondria and in a reconstituted system. In both experimental conditions, the rate of citrate transport, when compared to control, is greatly reduced (35-40%) in starved rats. Similar behaviour is shown by the cytosolic lipogenic enzymes. Kinetic analysis of the carrier activity in intact mitochondria and in the proteoliposomal system has showed that during starvation only the Vmax of this process decreases while there is no change in the Km. No difference in the Arrhenius plot and in the lipid composition has been detected, which indicates that the reduced transport activity in fasted animals is not due to a change in the carrier lipid microenvironment. In starved rats, a reduction of the carrier activity has occurred even after the addition of increasing cardiolipin concentrations to proteoliposomes. These findings thus suggest that starvation-induced decrease of citrate carrier activity could be due to a change of the intrinsic properties of the transport protein.

A haemorrhagic platelet disorder associated with altered stimulus-response coupling and abnormal membrane phospholipid composition

Haemorrhagic diatheses due to platelet function defects are a heterogenous and poorly understood group of conditions. We report the investigation of a female with a lifelong history of epistaxes, haemarthroses, menorrhagia and persistent iron-deficiency anaemia. Although platelet numbers and morphology were normal, platelet function was abnormal both in vivo and in vitro. Skin bleeding time was prolonged and aggregation thresholds in platelet-rich plasma to a variety of weak and strong agonists were increased. Platelet granule contents were normal and membrane glycoproteins GpIb and GpIIIa were present in normal amounts. Polyphosphoinositide metabolism and phosphatidic acid generation were diminished in thrombin-stimulated platelets, as was phosphorylation of the 47 kD substrate for protein kinase C and the 20 kD protein myosin light chain kinase, indicating impaired generation of the intracellular second messengers diacylglycerol and inositol trisphosphate due to diminished stimulated phospholipase C activity. Although intracellular free calcium, calmodulin activity and basal cAMP concentrations were normal, washed platelets showed increased cAMP accumulation following stimulation with prostaglandin E1 and forskolin. Platelet membrane lipid analysis revealed a reduction in plasmalogen phosphatidylethanolamine content. It is suggested that the membrane phospholipid abnormalities cause the abnormal platelet reactivity by interfering with signal transduction from platelet receptor, via intermediary G proteins, to phospholipase C and adenylate cylase. The bleeding tendency is likely to be a consequence of the altered stimulus-response coupling.

Electrophysiological properties of the hyperthyroid rat heart

We have studied the effects of in vivo administration of different T3 doses to thyroidectomized rats on electrophysiological properties, measured in vitro, of papillary muscle fibers. The treatment with increasing T3 doses was associated with a significant reduction of the action potential duration up to a dose as large as 25 micrograms/100 g body weight every second day. The treatment with larger doses of T3 tended to restore the values of the action potential duration present in animals treated with physiological doses (5 micrograms/100 g body weight every second day). Action potential duration is frequency dependent. As the stimulation rate was increased from 1 to 5 Hz, this duration increased in all groups. However the difference between the rat groups remained significant. The cardiac frequency measured in unanaesthetized rats increased as the T3 doses. Furthermore the intrinsic frequency showed a similar increase, indicating a direct effect of T3 on the pacemaker cells in all thyroid states. The mechanism of this action of the thyroid hormone is not, however clear.

Age-related changes in the hemostatic system

The increased incidence of arterial thromboembolism in the elderly has prompted investigation of age-related changes in the hemostatic system. Aging is associated with increased plasma levels of fibrinogen, factor VII and factor VIII, which have been shown to be risk factors for thrombotic disease in five large epidemiological studies. An increased responsiveness to different aggregating stimuli, elevated levels of beta-thromboglobulin and an increased production of thromboxane A2 were reported in the platelets of the elderly. These alterations are associated with modifications of platelet membrane lipid composition (namely an increase in the cholesterol/phospholipid ratio and a decrease in linoleic acid) with possible related changes in membrane fluidity. Moreover, a decrease in the number of platelet prostacyclin and thromboxane A2 receptors was observed with aging. Fibrinolytic activity is impaired in the elderly, probably due to an increase in plasminogen activator inhibitor 1. Interestingly, hypercoagulability has been demonstrated by an increase in the activation markers of the coagulation cascade (mainly fibrinopeptide A and prothrombin activation fragment F 1 + 2). Finally, clinical and experimental evidence suggests that endothelium could play a central role in hemostatic alterations which determine a thrombophilic state in the elderly.

Is lead toxicosis a reflection of altered fatty acid composition of membranes?

1. The premise of this review is that many of the biological effects of Pb are reflection of tissue peroxidation. 2. Enhanced tissue levels of arachidonic acid in Pb toxicosis appear to be involved in the peroxidative changes. 3. The altered arachidonate metabolism may be related to changes in membrane structure and function. 4. The induction of enhanced glutathione levels in animal tissues by Pb may afford protection from peroxidative damage.

Effect of dietary fats on some membrane-bound enzyme activities, membrane lipid composition and fatty acid profiles of rat heart sarcolemma

The effect of various dietary fats on membrane lipid composition, fatty acid profiles and membrane-bound enzyme activities of rat cardiac sarcolemma was assessed. Four groups of male weanling Charles Foster Young rats were fed diets containing 20% of groundnut, coconut, safflower or mustard oil for 16 weeks. Cardiac sarcolemma was prepared from each group and the activities of Na+, K(+)-ATPase, 5'-nucleotidase, Ca(2+)-ATPase and acetylcholinesterase were examined. ATPase activities were similar in all groups except the one fed coconut oil, which had the highest activities. Acetylcholinesterase activity was also similar in all the groups, however, it was significantly higher in the group fed mustard oil. No significant changes were observed among the groups in 5'-nucleotidase activity, in the cholesterol-to-phospholipid molar ratio and in sialic acid content. The coconut, safflower and mustard oil diets significantly increased cholesterol and phospholipid contents and the lipid-to-protein ratio of cardiac sarcolemma as compared to feeding the groundnut oil diet. The fatty acid composition of membrane lipids was quite different among the various groups, reflecting the type of dietary fat given. The total unsaturated-to-saturated fatty acid ratio was not different among the various groups; however, the levels of some major fatty acids such as palmitic (16:0), oleic (18:1) and linoleic (18:2) acids were significantly different. Cardiac sarcolemma of the group fed safflower oil had the highest polyunsaturated fatty acid content. The results suggest that dietary fats induce changes not only in the fatty acid composition of the component lipids but also in the activities of sarcolemmal enzymes involved in the regulation of cardiac function.

Thyroid hormones control lipid composition and membrane fluidity of skeletal muscle sarcolemma

Sarcolemma membrane lipid phase of skeletal muscles of hyperthyroid animals was compared to that of control (euthyroid) ones. Hyperthyroidism caused 15% decrease in cholesterol and 70% increase in the phospholipid content of the membrane. This was accompanied by the alterations in proportions between individual phospholipid classes, and was followed by changes in the composition of phospholipid fatty acids. The calculated fatty acid unsaturation index was higher for membrane lipid phase of hyperthyroid animals than of euthyroid ones. Thyroxine-induced alterations in the lipid composition of sarcolemma caused changes in the membrane fluidity and the activity of calmodulin-stimulated (Ca(2+)-Mg(2+)-ATPase. Measurements of the steady-state fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene indicated that the lipid phase transition of membrane vesicles occurred at 25.9 degrees C and at 28.9 degrees C for preparations isolated from hyperthyroid and euthyroid rabbits, respectively. Arrhenius plot break-point temperature for CaM-stimulated (Ca(2+)-Mg(2+)-ATPase activity was lower in membrane preparations isolated from hyperthyroid (26.9 degrees C) than from euthyroid ones (30.0 degrees C). Thus, the increase of the membrane fluidity presumably caused that the enzyme was characterized by the lower activation energy value. This phenomenon may be viewed as a supplementary mechanism for activation of the enzyme by thyroid hormones to previously reported elevation of the amount of (Ca(2+)-Mg(2+)-ATPase protein exerted by hyperthyroidism (Famulski et al. (1988) Eur. J. Biochem., 171, 363-368; Famulski and Wrzosek (1988) in The Ion Pumps-Structure, Function and Regulation (Stein, W.D., ed.), pp. 355-360, Alan R. Liss, New York).

Dietary fat and plasma lipid physical properties in swine

Changes in the lipid composition of swine lipoprotein were induced by feeding highly saturated or highly unsaturated diets. The diet higher in oleic acid, even when this was a highly unsaturated diet, resulted in a lower order parameter (more fluid) than in the other diets, as has been observed by others. This difference could be detected in whole unfractionated lipoprotein and in isolated high-density lipoprotein. Changes in order parameter with changes in cholesterol/triglyceride, reported by others, were not observed, possibly because of the weighted average effect of measuring whole plasma lipoprotein.

Feeding rats a diet enriched with saturated fatty acids prevents the inhibitory effects of acute and chronic ethanol exposure on the in vitro uptake of hexoses and lipids

Chow-fed rats were given 15% ethanol in their drinking water for 4 weeks, and then for the next 2 weeks of ethanol exposure they were fed isocaloric semisynthetic diets enriched in either saturated (S) or polyunsaturated (P, linoleic acid) fats. Food intake was lower in ethanol-fed (ETH) than in control (C) rats, but the average body weight gain was similar in ETH and C fed S or P. Intestinal dry weight and the percentage of the intestinal wall comprised of mucosa were more than 2-fold higher in ETH than C fed P, whereas these values were 50% lower in ETH than C fed S. The in vitro jejunal uptake of glucose and galactose was higher in ETH than C fed S, whereas the converse was true when feeding P. These effects were due to differences in the values of the maximal transport rate (Vmax), the Michaelis constant (Km), and the contribution of passive permeation. The relative permeability of the intestine to lipids was unchanged by giving ethanol or by feeding S or P, but the individual rates of uptake of most medium- and long-chain fatty acids and cholesterol were lower in ETH fed P as compared with S. In a second series of studies the acute effect of ethanol exposure was examined: animals were fed S or P for 2 weeks and the intestine was then removed: when 5% ethanol was added directly to the test solutions, there was lower in vitro jejunal and ileal uptake of glucose and higher jejunal uptake of 18:2 when rats were previously fed P, but not in those fed S. In summary; (1) feeding an isocaloric polyunsaturated fatty acid diet has a trophic effect on the intestinal mucosa of animals chronically drinking ethanol; and (2) feeding rats a diet enriched with saturated fatty acids prevents the inhibitory effects of acute and chronic ethanol exposure on the in vitro jejunal uptake of glucose, galactose and lipids observed in animals fed a polyunsaturated diet. Thus, the effect of chronic consumption of ethanol on the active and passive jejunal uptake of nutrients is influenced by the type of lipids in the animal's diet.

Lead-induced tissue fatty acid alterations and lipid peroxidation

Previous work showed that dietary lead (Pb) increases the relative concentration of arachidonic acid (20:4) as a percentage of total fatty acids, and decreases the relative proportion of linoleic acid (18:2) to arachidonic acid (18:2/20:4) in chick liver, serum, and erythrocyte membranes. The present investigation was undertaken to examine the time-course and magnitude of the fatty acid alterations with increasing dietary Pb levels. We also examined the effects of Pb on the fatty acid composition and lipid peroxide content of hepatic subcellular organelles. In Exp. 1, chicks were fed diets containing 0, 62.5, 125, 250, 500, or 1000 ppm added Pb (as Pb acetate trihydrate) from 1 to 21 d of age. After 21 d, no growth effects were observed; however, Pb lowered the 18:2/20:4 ratio and increased 20:4 concentration in total liver and serum lipids, and in total hepatic phospholipids in a dose-dependent manner. Hepatic mitochondrial membrane fatty acids were not altered, nor was there any increase in hepatic lipid peroxidation. In Exp.2, chicks were fed diets containing 0, 500, 1000, or 2000 ppm added Pb from 1 to 21 or 22 d of age. Pb depressed growth in a dose-dependent manner. In addition, Pb lowered the 18:2/20:4 ratio and increased 20:4 concentration in total liver lipids and in hepatic mitochondrial and microsomal membranes in a dose-dependent manner. Total hepatic lipid peroxidation was increased over control values by 1000 ppm Pb, and hepatic microsomal lipid peroxidation was increased by dietary Pb levels of 1000 and 2000 ppm. In Exp. 3, body weight, hepatic microsomal lipid peroxidation, and fatty acid composition were determined in 4-, 9-, 14-, 18-, and 23-d-old chicks fed 0 or 1500 ppm added Pb. Body weights of Pb-treated chicks were significantly lower than those of control chicks by day 18. Microsomal 20:4 concentration and peroxidation increased, and the 18:2/20:4 ratio decreased with age in both groups, but the changes were of greater magnitude in the Pb-treated chicks. The results suggest that some of the manifestations of Pb toxicity may be a reflection of increased concentration of 20:4 in specific membranes. Further, since the Pb-induced alterations in fatty acid composition were noted in the absence of any growth depression, we propose that fatty acid composition is more sensitive than growth rate to the presence of lead in the diet.

Interaction of receptors for prostaglandin E1/prostacyclin and insulin in human erythrocytes and platelets

Prostaglandin E1/I2 and insulin receptors of human erythrocyte and platelet are capable of modulating each other's activity. This modulation of the receptor activity and number in one system by a second receptor system in human platelet and erythrocyte seems to be beneficial. Insulin increases the PGE1 binding to platelets and thereby enhances the platelet antiaggregatory action of prostaglandin by increasing cyclic AMP levels. Similarly, PGE1 increases insulin binding to human erythrocyte, and thereby reduces the optimum concentration of insulin for a maximal reduction in membrane microviscosity. During ischemia the reduced response of platelets to the inhibitory effect of PGE1 or PGI2 relates to the impaired PGE1/I2 receptor activity. Treatment of these platelets with insulin at physiological concentrations can normalise the PGE1/I2 receptor activity. This review focuses on the relationship between the two receptor systems in human blood cells.

Unequal distribution of membrane components between pseudopodia and cell bodies of platelets

Platelet pseudopodia were compared to platelet cell bodies with respect to their lipid composition, fatty acid distribution and protein composition. The methodology for producing pseudopodial preparations of platelets stimulated with thrombin, ADP or calcium ionophore was established. The separation of pseudopodia and cell bodies was verified by electron microscopic examination of the respective platelet components. Lipid analyses demonstrated a preponderance of lysophospholipids and sphingomyelin in pseudopodial preparations and a large increase in mono-, di- and tri-ene fatty acids as compared to cell bodies. Changes were also evident in the protein composition evaluated by one- and two-dimensional SDS-polyacrylamide gel electrophoresis and by [32P]ATP labeling of exofacial membrane proteins. A protein of approximately 68 kDa which reacted strongly with antibody to PlA1, was prominantly displayed in platelet pseudopodia. Thus, our studies demonstrate a heterogeneous distribution of lipids and proteins in a mammalian membrane system which may have important implications for the functional behavior of the cell.

Erythrocyte membrane lipid alterations in undernourished cerebral palsied children during high intakes of a soy oil-based enteral formula

Five undernourished children with severe cerebral palsy (CP) were tube-fed sufficient volumes of Isocal to allow rapid weight gain. Isocal provided, on average, 88% of their daily energy intake for at least 25 days. The purpose of our study was to correct the undernutrition and to analyze the major erythrocyte phospholipids before and after feeding periods for possible feeding and disease-related differences. The fatty acid profiles of erythrocyte membranes from CP children were compared with those from 12 healthy children and with the fatty acid composition of the formula. There were no clinical or biochemical indications of essential fatty acid deficiency. The feeding of a soy oil-based formula increased the proportions of 18:2n-6 in the phospholipids. The increases occurred predominantly in phosphatidylcholine followed by phosphatidylethanolamine. Despite such large dietary intakes of soy oil, no changes were observed in the phospholipid concentrations of 20:4n-6, 18:3n-3, 20:5n-3, or in the C22n-6 and C22n-3 fatty acids. These findings are consistent with an inhibition of the delta 6 desaturase by high dietary linoleate.

Organic pesticides modify lipid-lipid and lipid-protein domains in model membranes. A laser Raman study

The effect of hexachlorocyclohexane (all isomers) on the thermal transition properties of phospholipid liposomes was determined by Raman spectroscopy. Raman spectra of liposomes with and without the presence of hexachlorocyclohexanes were recorded in the C-H stretching region which shows three major bands around 2850, 2880 and 2930 cm-1. Thermal transition properties were estimated from plots of I2880/I2850 and or I2930/I2850 vs. temperature, where I represents the intensity of the respective band. Our data on phospholipid liposomes reveal that delta- and gamma-hexachlorocyclohexanes drastically reduce and broaden the main thermal transitions of phospholipids at toxic level concentrations. These effects are more pronounced in liposomes containing 18 or more carbon atom long acyl chains. Alpha- and beta-isomers at similar concentrations show a minimum effect on the thermal transition properties of phospholipids. Raman analysis of phospholipid liposomes containing melittin, interestingly, reveal that the delta-isomer unlike the gamma-isomer strongly alters the transition properties of boundary lipids. These data suggest that the effect of hexachlorocyclohexanes on the thermal transition properties of membranes is stereo specific and that the delta-isomer preferably disrupts the lipid-protein domains. Results are explained on the basis of the dynamic flexibility owing to the equatorial and axial chlorine atoms of various hexachlorocyclohexane isomers.

Enhanced activity of the tricarboxylate carrier and modification of lipids in hepatic mitochondria from hyperthyroid rats

The effect of hyperthyroidism on the activity of the mitochondrial tricarboxylate carrier has been studied. The activity of this transporting system in liver mitochondria was quantitatively determined by the rate of malate-[14C]citrate exchange using the 1,2,3-benzene-tricarboxylate inhibitor stop technique. It has been found that the rate of citrate uptake is significantly enhanced in liver mitochondria from hyperthyroid rats as compared to that obtained in mitochondria from control rats. Kinetic analysis of the malate-citrate exchange reaction indicates that only the Vmax of this transporting process is enhanced, while there is practically no change in the Km values. Inhibitor titrations with the inhibitor palmitoyl-CoA show that mitochondria from hyperthyroid rats require the same concentrations of inhibitor to produce 100% inhibition of citrate uptake as control mitochondria, suggesting that the amount of functional translocase enzyme present is unaffected. The Arrhenius plot characteristics differ for tricarboxylate carrier activity in mitochondria from hyperthyroid rats as compared with control rats in that the break point of the biphasic plot decreases from 18.1 +/- 1.4 degrees C in controls to 12.9 +/- 1.2 degrees C in hyperthyroid animals. The hepatic mitochondrial lipid composition is altered significantly in hyperthyroid rats; the total cholesterol decreases and the phospholipids increase. The liver mitochondrial phospholipid composition is altered significantly in hyperthyroid rats. In particular negatively charged phospholipid cardiolipin increases by more than 50%. Minor alterations were found in the pattern of fatty acids. The thyroid hormone induced change in the activity of the tricarboxylate carrier can be ascribed either to a general modification of membrane lipid composition which increases the membrane fluidity and in turn the mobility of the carrier or to a more localized change of lipid domain (cardiolipin content) surrounding the carrier molecule in the mitochondrial membrane.

Characteristics of sorbitol uptake in rat glial primary cultures

Uptake of [U-14C]sorbitol was studied in astrogliarich rat primary cultures. Initial rate of sorbitol uptake is proportional to sorbitol concentration between 20 microM and 400 mM. Sorbitol transport is not inhibited by glucose, fructose, and a variety of structurally related polyols, or by cytochalasin B, an inhibitor of glucose transport. Phloretin, phlorizin, filipin, and n-hexanol, all compounds that alter the properties of biological membranes, and the sulfhydryl reagent p-chloromercuribenzoate inhibit sorbitol uptake to various degrees. Variation in the concentrations of extracellular Na+ and K+ does not affect transfer of sorbitol across the cell membrane. It is concluded that sorbitol is taken up into glial cells by a diffusion process, not involving a carrier and probably not through the lipid bilayer, but through a proteinaceous channel-like structure.

Calmodulin selectively modulates the guanylate cyclase activity by repressing the lipid phase separation temperature in the inner half of the bilayer of rat brain synaptosomal plasma membranes

The association of [125I-]calmodulin with rat brain synaptosomal plasma membranes, when incubated for 1 h at 25 degrees in the presence or in absence of 20 microM Ca2+, follows a sigmoid path with a Hill coefficient h = 1.79 +/- 0.12 and h = 1.72 +/- 0.11, respectively. The total association of calmodulin with the membrane increased approx. 60%-80% at all the range of calmodulin concentrations used in the presence of 20 microM Ca2+. A three fold increase of guanylate cyclase activity was shown in the presence of low concentrations of calmodulin (up to 10 nM); higher concentrations (up to 40 nM) however, led to a progressive inhibition of the enzyme activity with respect to maximal stimulation. Calmodulin increased the lipid fluidity of synaptosomal plasma membranes labeled with 1,6-diphenyl-1,3,5-hexatriene (DPH), as indicated by the steady-state fluorescence anisotropy [(ro/r)-1]-1. Arrhenius-type plots of [(ro/r)-1]-1 indicated that the lipid separation of the membrane at 22.7 +/- 1.2 degrees was perturbed by calmodulin such that the temperature was reduced to 16.3 +/- 0.9 degrees and 15.5 +/- 0.8 degrees in the absence or in the presence of 20 microM Ca2+. Arrhenius plots of guanylate cyclase and acetylcholinesterase activities exhibited break points at 26.7 +/- 1.4 degrees and 22.3 +/- 1.0 degrees in control synaptosomal plasma membranes, respectively. The break point for the guanylate cyclase was reduced to 16.3 +/- 0.9 degrees in calmodulin treated synaptosomal plasma membranes whereas that of acetylcholinesterase remained unaffected (21.1 +/- 0.9 degrees).(ABSTRACT TRUNCATED AT 250 WORDS)