The involvement of phosphatidylserine in adenosine triphosphatase activity of the sodium pump

Measuring enzyme activities in crude homogenates: Na+/K+-ATPase as a case study in optimizing assays

In this review of assays of Na⁺/K⁺-ATPase (NKA), we explore the choices made by researchers assaying the enzyme to investigate its role in physiological regulation. We survey NKA structure and function in the context of how it is typically assayed, and how technical choices influence what can be said about the enzyme. In comparing different methods for extraction and assay of NKA, we identified a series of common pitfalls that compromise the veracity of results. We include experimental work to directly demonstrate how choices in detergents, salts and substrates influence NKA activities measured in crude homogenates. Our review of assay approaches integrates what is known from enzymology, biomedical physiology, cell biology and evolutionary biology, offering a more robust method for assaying the enzyme in meaningful ways, identifying caveats and future directions to explore its structure and function. The goal is to provide the sort of background on the enzyme that should be considered in exploring the function of the enzyme in comparative physiology.

Evaluation of the Erythrocyte Membrane in Head and Neck Cancer Patients

Head and neck squamous cell carcinoma (HNSCC) is a heterogeneous and complex disease, both from a clinical and molecular point of view. The prolonged use of alcohol and tobacco, along with the release of tumor secretions can modulate blood cells, such as erythrocytes. Here, this study was conducted with 24 patients diagnosed with HNSCC and an equal number of healthy individuals are matched by age and gender. The levels of lipid peroxidation were measured using the individual plasma, while for lipid concentrations, identification and quantification Na, K-ATPase activity and osmotic fragility, the red blood cell concentrate were used. The release of TBARS was significantly higher in patients with HNSCC. The lipid profile assays demonstrated a rearrangement of the erythrocyte membrane due to a decrease in total phospholipids and phosphatidylethanolamine followed by an increase in total cholesterol and phosphatidylcholine. Na, K-ATPase activity also increased. Erythrocytes were more fragile in patients with HNSCC than in health individuals. Therefore, the membrane of erythrocytes were rearranged and Na, K-ATPase function altered in the HNSCC patients. Our findings suggests that the alcohol, tobacco and tumor secretion modulate in a specific manner that the erythrocytes membranes of these patients making this system a potential tool for HNSCC biomarker of tumor progression.

General and specific interactions of the phospholipid bilayer with P-type ATPases

Protein structure and function are modulated via interactions with their environment, representing both the surrounding aqueous media and lipid membranes that have an active role in shaping the structural topology of membrane proteins. Compared to a decade ago, there is now an abundance of crystal structural data on membrane proteins, which together with their functional studies have enhanced our understanding of the salient features of lipid-protein interactions. It is now important to recognize that membrane proteins are regulated by both (1) general lipid-protein interactions, where the general physicochemical properties of the lipid environment affect the conformational flexibility of a membrane protein, and (2) by specific lipid-protein interactions, where lipid molecules directly interact via chemical interactions with specific lipid-binding sites located on the protein. However, due to local differences in membrane composition, thickness, and lipid packing, local membrane physical properties and hence the associated lipid-protein interactions also differ due to membrane location, even for the same protein. Such a phenomenon has been shown to be true for one family of integral membrane ion pumps, the P2-type adenosine triphosphatases (ATPases). Despite being highly homologous, individual members of this family have distinct structural and functional activity and are an excellent candidate to highlight how the local membrane physical properties and specific lipid-protein interactions play a vital role in facilitating the structural rearrangements of these proteins necessary for their activity. Hence in this review, we focus on both the general and specific lipid-protein interactions and will mostly discuss the structure-function relationships of the following P2-type ATPases, Na⁺,K⁺-ATPase (NKA), gastric H⁺,K⁺-ATPase (HKA), and sarco(endo)plasmic reticulum Ca²⁺-ATPase (SERCA), in concurrence with their lipid environment.

Greasing the wheels or a spanner in the works? Regulation of the cardiac sodium pump by palmitoylation

The ubiquitous sodium/potassium ATPase (Na pump) is the most abundant primary active transporter at the cell surface of multiple cell types, including ventricular myocytes in the heart. The activity of the Na pump establishes transmembrane ion gradients that control numerous events at the cell surface, positioning it as a key regulator of the contractile and metabolic state of the myocardium. Defects in Na pump activity and regulation elevate intracellular Na in cardiac muscle, playing a causal role in the development of cardiac hypertrophy, diastolic dysfunction, arrhythmias and heart failure. Palmitoylation is the reversible conjugation of the fatty acid palmitate to specific protein cysteine residues; all subunits of the cardiac Na pump are palmitoylated. Palmitoylation of the pump's accessory subunit phospholemman (PLM) by the cell surface palmitoyl acyl transferase DHHC5 leads to pump inhibition, possibly by altering the relationship between the pump catalytic α subunit and specifically bound membrane lipids. In this review, we discuss the functional impact of PLM palmitoylation on the cardiac Na pump and the molecular basis of recognition of PLM by its palmitoylating enzyme DHHC5, as well as effects of palmitoylation on Na pump cell surface abundance in the cardiac muscle. We also highlight the numerous unanswered questions regarding the cellular control of this fundamentally important regulatory process.

Unique Lipid Chemistry of Synaptic Vesicle and Synaptosome Membrane Revealed Using Mass Spectrometry

Synaptic vesicles measuring 30-50 nm in diameter containing neurotransmitters either completely collapse at the presynaptic membrane or dock and transiently fuse at the base of specialized 15 nm cup-shaped lipoprotein structures called porosomes at the presynaptic membrane of synaptosomes to release neurotransmitters. Recent study reports the unique composition of major lipids associated with neuronal porosomes. Given that lipids greatly influence the association and functions of membrane proteins, differences in lipid composition of synaptic vesicle and the synaptosome membrane was hypothesized. To test this hypothesis, the lipidome of isolated synaptosome, synaptosome membrane, and synaptic vesicle preparation were determined by using mass spectrometry in the current study. Results from the study demonstrate the enriched presence of triacyl glycerols and sphingomyelins in synaptic vesicles, as opposed to the enriched presence of phospholipids in the synaptosome membrane fraction, reflecting on the tight regulation of nerve cells in compartmentalization of membrane lipids at the nerve terminal.

Specific phospholipid binding to Na,K-ATPase at two distinct sites

Membrane protein function can be affected by the physical state of the lipid bilayer and specific lipid-protein interactions. For Na,K-ATPase, bilayer properties can modulate pump activity, and, as observed in crystal structures, several lipids are bound within the transmembrane domain. Furthermore, Na,K-ATPase activity depends on phosphatidylserine (PS) and cholesterol, which stabilize the protein, and polyunsaturated phosphatidylcholine (PC) or phosphatidylethanolamine (PE), known to stimulate Na,K-ATPase activity. Based on lipid structural specificity and kinetic mechanisms, specific interactions of both PS and PC/PE have been inferred. Nevertheless, specific binding sites have not been identified definitively. We address this question with native mass spectrometry (MS) and site-directed mutagenesis. Native MS shows directly that one molecule each of 18:0/18:1 PS and 18:0/20:4 PC can bind specifically to purified human Na,K-ATPase (α₁β₁). By replacing lysine residues at proposed phospholipid-binding sites with glutamines, the two sites have been identified. Mutations in the cytoplasmic αL8-9 loop destabilize the protein but do not affect Na,K-ATPase activity, whereas mutations in transmembrane helices (TM), αTM2 and αTM4, abolish the stimulation of activity by 18:0/20:4 PC but do not affect stability. When these data are linked to crystal structures, the underlying mechanism of PS and PC/PE effects emerges. PS (and cholesterol) bind between αTM 8, 9, 10, near the FXYD subunit, and maintain topological integrity of the labile C terminus of the α subunit (site A). PC/PE binds between αTM2, 4, 6, and 9 and accelerates the rate-limiting E₁P-E₂P conformational transition (site B). We discuss the potential physiological implications.

Membrane Lipid Microenvironment Modulates Thermodynamic Properties of the Na+-K+-ATPase in Branchial and Intestinal Epithelia in Euryhaline Fish In vivo

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 seabream Sparus 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 of Td between 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 of Ea₁, ΔH^‡ and ΔS^‡ for the Na⁺-K⁺-ATPase were all increased, while Td values 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 cholesterol in vivo. Thus, Td was positively related to 18:1n-9 and negatively to DHA. Td, Ea₁ and 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⁺-ATPase in 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.

General and specific lipid-protein interactions in Na,K-ATPase

The molecular activity of Na,K-ATPase and other P2 ATPases like Ca(2+)-ATPase is influenced by the lipid environment via both general (physical) and specific (chemical) interactions. Whereas the general effects of bilayer structure on membrane protein function are fairly well described and understood, the importance of the specific interactions has only been realized within the last decade due particularly to the growing field of membrane protein crystallization, which has shed new light on the molecular details of specific lipid-protein interactions. It is a remarkable observation that specific lipid-protein interactions seem to be evolutionarily conserved, and conformations of specifically bound lipids at the lipid-protein surface within the membrane are similar in crystal structures determined with different techniques and sources of the protein, despite the rather weak lipid-protein interaction energy. Studies of purified detergent-soluble recombinant αβ or αβFXYD Na,K-ATPase complexes reveal three separate functional effects of phospholipids and cholesterol with characteristic structural selectivity. The observations suggest that these three effects are exerted at separate binding sites for phophatidylserine/cholesterol (stabilizing), polyunsaturated phosphatidylethanolamine (stimulatory), and saturated PC or sphingomyelin/cholesterol (inhibitory), which may be located within three lipid-binding pockets identified in recent crystal structures of Na,K-ATPase. The findings point to a central role of direct and specific interactions of different phospholipids and cholesterol in determining both stability and molecular activity of Na,K-ATPase and possible implications for physiological regulation by membrane lipid composition. This article is part of a special issue titled "Lipid-Protein Interactions."

Stimulation, inhibition, or stabilization of Na,K-ATPase caused by specific lipid interactions at distinct sites

The activity of membrane proteins such as Na,K-ATPase depends strongly on the surrounding lipid environment. Interactions can be annular, depending on the physical properties of the membrane, or specific with lipids bound in pockets between transmembrane domains. This paper describes three specific lipid-protein interactions using purified recombinant Na,K-ATPase. (a) Thermal stability of the Na,K-ATPase depends crucially on a specific interaction with 18:0/18:1 phosphatidylserine (1-stearoyl-2-oleoyl-sn-glycero-3-phospho-L-serine; SOPS) and cholesterol, which strongly amplifies stabilization. We show here that cholesterol associates with SOPS, FXYD1, and the α subunit between trans-membrane segments αTM8 and -10 to stabilize the protein. (b) Polyunsaturated neutral lipids stimulate Na,K-ATPase turnover by >60%. A screen of the lipid specificity showed that 18:0/20:4 and 18:0/22:6 phosphatidylethanolamine (PE) are the optimal phospholipids for this effect. (c) Saturated phosphatidylcholine and sphingomyelin, but not saturated phosphatidylserine or PE, inhibit Na,K-ATPase activity by 70-80%. This effect depends strongly on the presence of cholesterol. Analysis of the Na,K-ATPase activity and E1-E2 conformational transitions reveals the kinetic mechanisms of these effects. Both stimulatory and inhibitory lipids poise the conformational equilibrium toward E2, but their detailed mechanisms of action are different. PE accelerates the rate of E1 → E2P but does not affect E2(2K)ATP → E13NaATP, whereas sphingomyelin inhibits the rate of E2(2K)ATP → E13NaATP, with very little effect on E1 → E2P. We discuss these lipid effects in relation to recent crystal structures of Na,K-ATPase and propose that there are three separate sites for the specific lipid interactions, with potential physiological roles to regulate activity and stability of the pump.

Neuronal porosome lipidome

Cup-shaped lipoprotein structures called porosomes are the universal secretory portals at the cell plasma membrane, where secretory vesicles transiently dock and fuse to release intravesicular contents. In neurons, porosomes measure ∼15 nm and are comprised of nearly 40 proteins, among them SNAREs, ion channels, the G_αo G-protein and several structural proteins. Earlier studies report the interaction of specific lipids and their influence on SNAREs, ion channels and G-protein function. Our own studies demonstrate the requirement of cholesterol for the maintenance of neuronal porosome integrity, and the influence of lipids on SNARE complex assembly. In this study, to further understand the role of lipids on porosome structure-function, the lipid composition of isolated neuronal porosome was determined using mass spectrometry. Using lipid-binding assays, the affinity of porosome-associated syntaxin-1A to various lipids was determined. Our mass spectrometry results demonstrate the presence of phosphatidylinositol phosphates (PIP's) and phosphatidic acid (PA) among other lipids, and the enriched presence of ceramide (Cer), lysophosphatidylinositol phosphates (LPIP) and diacylglycerol (DAG). Lipid binding assays demonstrate the binding of neuronal porosome to cardiolipin, and confirm its association with PIP's and PA. The ability of exogenous PA to alter protein–protein interaction and neurotransmitter release is further demonstrated from the study.

The effect of gamma radiation on the lipid profile of irradiated red blood cells

An investigation into the effects of irradiation and of the storage time on aging and quality are a relevant issue to ensure the safety and the efficiency of irradiation in the prevention of transfusion-associated graft-versus-host disease (TA-GVHD). In this work, the biochemical properties and alterations presented by erythrocyte membranes, up to 28-days post-irradiation, with a dose of 25 Gy, were studied as a function of storage and post-irradiation time. There was a considerable variation in the total of phospholipid content, when comparing the control and irradiated samples, mostly from the third day onwards; and at the same time, the effect occurred as a function on the storage time of blood bags. The levels of total cholesterol decreased 3-9 days after irradiation. TBARS levels were increased after irradiation and 7 days of storage, but no increment of catalase activity was observed after the irradiation. Furthermore, the protein profile was maintained throughout the irradiation and storage time, until the 21st day, with the presence of a protein fragmentation band of around 28 kDa on the 28th day. In conclusion, although gamma irradiation is the main agent for the prevention of TA-GVHD, a better understanding of the physical and biochemical properties of erythrocytes are necessary to better assess their viability, and to be able to issue more secure recommendations on the shelf life of blood bags, and the safe use of the irradiated red cells therein.

Neutral phospholipids stimulate Na,K-ATPase activity: a specific lipid-protein interaction

Membrane proteins interact with phospholipids either via an annular layer surrounding the transmembrane segments or by specific lipid-protein interactions. Although specifically bound phospholipids are observed in many crystal structures of membrane proteins, their roles are not well understood. Na,K-ATPase is highly dependent on acid phospholipids, especially phosphatidylserine, and previous work on purified detergent-soluble recombinant Na,K-ATPase showed that phosphatidylserine stabilizes and specifically interacts with the protein. Most recently the phosphatidylserine binding site has been located between transmembrane segments of αTM8-10 and the FXYD protein. This paper describes stimulation of Na,K-ATPase activity of the purified human α1β1 or α1β1FXYD1 complexes by neutral phospholipids, phosphatidylcholine, or phosphatidylethanolamine. In the presence of phosphatidylserine, soy phosphatidylcholine increases the Na,K-ATPase turnover rate from 5483 ± 144 to 7552 ± 105 (p < 0.0001). Analysis of α1β1FXYD1 complexes prepared with native or synthetic phospholipids shows that the stimulatory effect is structurally selective for neutral phospholipids with polyunsaturated fatty acyl chains, especially dilinoleoyl phosphatidylcholine or phosphatidylethanolamine. By contrast to phosphatidylserine, phosphatidylcholine or phosphatidylethanolamine destabilizes the Na,K-ATPase. Structural selectivity for stimulation of Na,K-ATPase activity and destabilization by neutral phospholipids distinguish these effects from the stabilizing effects of phosphatidylserine and imply that the phospholipids bind at distinct sites. A re-examination of electron densities of shark Na,K-ATPase is consistent with two bound phospholipids located between transmembrane segments αTM8-10 and TMFXYD (site A) and between TM2, -4, -6, -and 9 (site B). Comparison of the phospholipid binding pockets in E2 and E1 conformations suggests a possible mechanism of stimulation of Na,K-ATPase activity by the neutral phospholipid.

Correlation between the activities and the oligomeric forms of pig gastric H/K-ATPase

Membrane-bound H/K-ATPase was solubilized by octaethylene glycol dodecyl ether (C(12)E(8)) or n-octyl glucoside (nOG). H/K-ATPase activity and the distribution of protomeric and oligomeric components were evaluated by high-performance gel chromatography (HPGC) and by single-molecule detection using total internal reflection fluorescence microscopy (TIRFM). As evidenced by HPGC of the C(12)E(8)-solubilized enzyme, the distribution of oligomers was 12% higher oligomeric, 44% diprotomeric, and 44% protomeric species, although solubilization by C(12)E(8) reduced the H/K-ATPase activity to 1.8% of that of the membrane-bound enzyme. The electron microscopic images of the C(12)E(8)-solubilized enzyme showed the presence of protomers and a combination of two and more protomers. While the nOG-solubilized H/K-ATPase retained the same turnover number and 71% of the specific activity as that of the membrane-bound enzyme, 56% higher oligomeric, 34% diprotomeric, and 10% protomeric species were detected. TIRFM analysis of solubilized fluorescein 5'-isothiocyanate (FITC)-modified H/K-ATPase at Lys-518 of the alpha-chain showed a quantized photobleaching of the FITC fluorescence intensity. For the C(12)E(8)-solubilized FITC-enzyme, the fraction of each of the initial relative fluorescence intensity units of 4, 2, and 1 was, respectively, 5%, 44% and 51%. In the case of the nOG-solubilized FITC-enzyme, each fraction of 4 and 2 units was, respectively, 54% and 46% with no detectable 1 unit fraction. This represents the first direct observation of H/K-ATPase in aqueous solution. The correlation between the enzymatic activities and distribution of oligomeric forms of H/K-ATPase by HPGC and the observation of a single molecule of H/K-ATPase and others suggests that the tetraprotomeric form of H/K-ATPase molecules represents the functional species in the membrane.

Monoclonal antibody to phosphatidylserine inhibits Na+/K(+)-ATPase activity

A monoclonal IgG, directed to phosphatidylserine (PS1G3), partially (40-50%) inhibited Na+/K(+)-ATPase activity (forward running reaction cycle) without affecting the K0.5 values for Na+,K+ and MgATP. The Hill or interaction coefficients (nH) for Na+ and K+ for this reaction were reduced from 3.0 to 1.6 and from 1.6 to 0.8, respectively. The K(+)-stimulated p-nitrophenylphosphatase activity (p-NPPase), which is a partial reaction sequence of the Na+/K(+)-ATPase system (but in the backward running mode), was inhibited more strongly (about 70%) due to an increase in K+/substrate antagonism. In this system K0.5 and nH values for both p-nitrophenyl phosphate (p-NPP) and K+ were increased by the mAb. At the maximally inhibitory concentration of PS1G3 the Vmax of the p-NPPase was also reduced. Partial reactions, which were inhibited by PS1G3, are: (1) the Na(+)-activated phosphorylation (non-competitive vs. Na+), (2) the Rb+ occlusion (competitive vs. Rb+). Partial reactions not harmed by PS1G3 are: (3) the K(+)-dependent dephosphorylation, (4) the K(+)-dependent E1 + K+<-->E2K transition. We conclude that PtdSer is involved in cation occlusion, possibly by forming part of the access gate.

Sequential preparation of highly purified microvillous and basal syncytiotrophoblast membranes in substantial yield from a single term human placenta: inhibition of microvillous alkaline phosphatase activity by EDTA

The human placental syncytiotrophoblast is a highly polarised epithelial layer responsible for regulating materno-fetal exchange. We here describe a novel procedure for isolating paired fractions of the maternal-facing and fetal-facing plasma membranes from this syncytium, from a single placenta, without the need for homogenisation procedures. This reduces the potential for contamination of these membrane fractions by intracellular membranes, or from plasma membranes from other cell types within the placenta. Microvillous membrane vesicles (MVM) were obtained by gentle stirring of dispersed villous tissue. The tissue sedimented at the end of this procedure was subjected to sequential ultrasonication to release the basal membrane (BM). Crude MVM was subsequently purified on a discontinuous sucrose gradient. Crude BM was further purified using either discontinuous Ficoll or sucrose gradients. The Ficoll procedure, while producing a BM fraction extremely enriched in marker enzyme, resulted in unacceptably low protein recoveries and hence the sucrose gradient procedure was also adopted for BM. Yields for MVM and BM produced on sucrose density gradients approached 30 mg/100 g tissue. The MVM fraction was composed of vesicles of 232 +/- 9 (S.E.) nm diameter of which nearly 90% were 'right side out'. These membranes were 37-fold enriched in the marker enzyme alkaline phosphatase. Purified BM vesicles were 317 +/- 14 nm in diameter, also approximately 90% 'right side out' and over 40-fold enriched in dihydroalprenolol binding. Cross-contamination or contamination from intracellular membranes was negligible. MVM alkaline phosphatase activity was shown to be inhibitable in a dose- and time-dependent manner by EDTA present in the storage buffer.

Esophageal cancer phospholipid characterization by 31P NMR

Phospholipid extracts of surgical tissue specimens from 18 patients, consisting of normal esophagus, distal esophageal tumor and normal stomach, were analyzed using 31P NMR. The prominent phospholipids detected in these tissues included cardiolipin (CL), phosphatidylethanolamine plasmalogen, phosphatidylethanolamine (PE), phosphatidylserine (PS), sphingomyelin (SPH), phosphatidylinositol (PI), phosphatidylcholine plasmalogen and phosphatidylcholine (PC). Very small quantities of the phospholipids lysophosphatidylcholine, phosphatidic acid, phosphatidylglycerol, and an uncharacterized phospholipid at -0.13 delta also were detected in some of the 54 tissue specimens analyzed. The mean relative concentrations of these phospholipids, in mole percentages of total detected phosphorus, were determined from the acquired spectra and used to differentiate among the three tissue groups. The relative concentrations of the following phospholipids differed significantly (p < 0.001) among the respective tissue groups: normal esophagus vs esophageal tumor, PS, SPH, PI, PC; normal esophagus vs normal stomach, CL, PE, PS, SPH; esophageal tumor vs normal stomach, CL, PE. Membrane phospholipids implicated in modulating the growth and metastases of tumors of epithelial origin can be profiled to discriminate among normal esophagus, distal esophageal tumor and normal stomach using 31P NMR.

Effects of exercise training and anabolic steroids on plantaris and soleus phospholipids: a 31P nuclear magnetic resonance study

1. The purpose of this study was to examine the effect of exercise, anabolic steroid treatment, and a combination of both treatments on the phospholipid composition of predominantly fast twitch (plantaris) and slow twitch (soleus) skeletal muscles. The 4 experimental groups analyzed were sedentary control (C), steroid-treated (S), exercise-trained (E), and exercise plus steroid-treated (ES). 2. Among the 11 phospholipids quantitated, for the plantaris muscle, phosphatidylcholine was reduced in ES relative to C, while phosphatidylethanolamine and phosphatidylethanolamine plasmalogen were elevated in E and ES relative to C. For the soleus muscle, phosphatidylserine was reduced in S and E relative to C, and cardiolipin was elevated in E relative to C. 3. Of the 27 metabolic indices calculated for the plantaris, 15 changed significantly among E and ES relative to S and C, while for the soleus, only three indices changed among the four groups, two among E and ES relative to S and C and one between S and C. 4. For the plantaris muscle, the results are consistent with an exercise-induced alteration of membrane phospholipid composition that increases ion translocation activity. For the soleus muscle, this membrane alteration essentially does not take place. 5. Steroid treatment had little to no statistically significant effect on plantaris and soleus muscle phospholipid systems, regardless of the imposed regimen.

Change in oligomeric structure of solubilized Na+/K(+)-ATPase induced by octaethylene glycol dodecyl ether, phosphatidylserine and ATP

Membrane-bound Na+/K(+)-ATPase purified from dog kidney was solubilized with octaethylene glycol dodecyl ether (C12E8), and the resultant solubilized enzyme was chromatographed on a TSKgel G4000SWXL or G3000SWXL column equilibrated with elution buffers containing various ligands affecting oligomerization of the enzyme. Weight-averaged molecular weight (Mw) values for the main protein components eluted were estimated by low-angle laser light-scattering photometry. With increasing concentration of C12E8 included in the elution buffer from 0.1 to 5 mg/ml, the Mw decreased from 230,000 to 153,000, indicating that C12E8 induced dissociation of the enzyme. In contrast, the Mw of the protein component increased up to 1.44.10(6) as the concentration of phosphatidylserine (PS) added to the elution buffer containing a fixed concentration of 0.3 mg/ml C12E8 was increased to 120 micrograms/ml. The association and/or aggregation were reversible by removal of the PS by rechromatography. Addition of PS to the elution buffer also allowed the solubilized enzyme to exhibit ATPase activity comparable to that of the membrane-bound enzyme during passage through the column. This was also the case with phosphatidylglycerol (PG) and phosphatidylinositol, but not with phosphatidylcholine or phosphatidylethanolamine. The specific refractive index increment (dn/dcp) of the solubilized enzyme was increased by addition of exogenous PG or PS, strongly suggesting that the phospholipid became bound to the enzyme, and that it induced association of the enzyme. The association induced by PS was inhibited by ATP and ADP, but not AMP. The concentrations for half-maximal inhibition were 0.44 mM for ATP and 0.88 mM for ADP. The PS-induced associated enzyme isolated by chromatography in the presence of 120 micrograms/ml PS was dissociated by ATP with K0.5 of 0.16 mM. The dissociating effect of C12E8, ATP and ADP and the associating effect of PS on the solubilized enzyme are consistent with the reports that C12E8 mimics the effect of regulatory ATP at the low-affinity site on the conformational transition from E2 to E1, and that phospholipids are essential for the reverse transition from E1 to E2. The results can be explained by assuming that the enzyme takes the form of a loosely associated diprotomer in the E1 state and a tightly associated one in the E2 state.

Protective action of phosphatidylserine on stress-induced behavioral and autonomic changes in aged rats

Phosphatidylserine (PS) was administered in aged rats subjected to various stressor stimuli in order to evaluate its effect on grooming behavior, core temperature and gastric ulcers. Novelty-induced grooming appeared to be increased in aged rats as compared to young controls. The subchronic intraperitoneal treatment with PS (20 mg/kg/day for 20 days) decreased grooming activity in aged rats, whereas it did not affect that of young animals. Restraint stress induced hyperthermia in both aged and young rats. However, 90 min after the beginning of restraint, PS-treated old rats showed a normalization of core temperature. Furthermore, restraint-plus-cold stress induced gastric ulcers in both aged and young rats. The treatment with PS was followed by a decreased incidence of gastric lesions in aged, but not in young rats. The mechanism of PS protective action against stress-induced behavioral and autonomic changes is unknown, but it may involve the brain level as this drug exerts a noteworthy influence on behavior and autonomic functions.

Lipids of nervous tissue: composition and metabolism

As indicated in the Introduction, the many significant developments in the recent past in our knowledge of the lipids of the nervous system have been collated in this article. That there is a sustained interest in this field is evident from the rather long bibliography which is itself selective. Obviously, it is not possible to summarize a review in which the chemistry, distribution and metabolism of a great variety of lipids have been discussed. However, from the progress of research, some general conclusions may be drawn. The period of discovery of new lipids in the nervous system appears to be over. All the major lipid components have been discovered and a great deal is now known about their structure and metabolism. Analytical data on the lipid composition of the CNS are available for a number of species and such data on the major areas of the brain are also at hand but information on the various subregions is meagre. Such investigations may yet provide clues to the role of lipids in brain function. Compared to CNS, information on PNS is less adequate. Further research on PNS would be worthwhile as it is amenable for experimental manipulation and complex mechanisms such as myelination can be investigated in this tissue. There are reports correlating lipid constituents with the increased complexity in the organization of the nervous system during evolution. This line of investigation may prove useful. The basic aim of research on the lipids of the nervous tissue is to unravel their functional significance. Most of the hydrophobic moieties of the nervous tissue lipids are comprised of very long chain, highly unsaturated and in some cases hydroxylated residues, and recent studies have shown that each lipid class contains characteristic molecular species. Their contribution to the properties of neural membranes such as excitability remains to be elucidated. Similarly, a large proportion of the phospholipid molecules in the myelin membrane are ethanolamine plasmalogens and their importance in this membrane is not known. It is firmly established that phosphatidylinositol and possibly polyphosphoinositides are involved with events at the synapse during impulse propagation, but their precise role in molecular terms is not clear. Gangliosides, with their structural complexity and amphipathic nature, have been implicated in a number of biological events which include cellular recognition and acting as adjuncts at receptor sites. More recently, growth promoting and neuritogenic functions have been ascribed to gangliosides. These interesting properties of gangliosides wIll undoubtedly attract greater attention in the future.(ABSTRACT TRUNCATED AT 400 WORDS)

Influence of phosphatidylserine on (Na+ + K+)-stimulated ATPase and acetylcholinesterase activities of dog brain synaptosomal plasma membranes

Phosphatidylserine (PtdSer) incubated with synaptosomal plasma membranes (SPM) of dog brain is incorporated into SPM in proportion to its concentration in the incubation medium. Low PtdSer concentrations progressively activated the SPM-associated (Na+ + K+)-stimulated ATPase and acetylcholinesterase. Increasing the PtdSer concentration above that which maximally stimulated the enzyme activities effected a progressive inhibition with respect to maximal stimulation. Arrhenius plots of (Na+ + K+ + Mg2+)-dependent ATPase and 5'-nucleotidase revealed a clear break at 23-24 degrees C for both enzymes in SPM untreated with PtdSer (controls), whereas a linear relation was obtained for SPM treated with PtdSer. Changes in the allosteric properties of (Na+ + K+)-stimulated ATPase by fluoride (F-) and/or of 5'-nucleotidase by concanavalin A (i.e. changes of Hill coefficients) indicate that PtdSer increases the membrane fluidity. These results suggest that modifications of lipid-protein interactions in SPM induced by PtdSer may have implications in the physiological processes in the central nervous system.

Mechanisms of the fasting-induced dissociation of insulin binding from its action in isolated rat hepatocytes

Fasting leads to an increase in insulin binding to isolated rat hepatocytes from 12 to 17%. This increase was accounted for by changes in the affinity of insulin receptors without alteration in their number. In contrast, the responsiveness of hepatocytes to insulin was markedly diminished in fasted rats. Both basal and insulin-stimulated rates of 14C-glucose incorporation into glycogen were significantly decreased in fasted animals. When insulin-induced 14C-glucose incorporation into glycogen was expressed as a percent above the basal rate, hepatocytes isolated both from control and fasted animals showed the same magnitude of maximal response (66 +/- 13% in fed and 59 +/- 12% in fasted animals, respectively). However, more insulin must be bound to hepatocytes isolated from fasted animals in order to elicit the same percent of insulin's maximal effect. Incubation of 'fed' hepatocytes in the serum obtained from fasted rats significantly diminished their responsiveness to insulin. An addition of insulin (100 ng/ml), glucose (10 mM) and antibodies to glucagon (1:100) eliminated the inhibitory effect of 'fasted' serum on 'fed' hepatocytes. A 48-hour fast increased significantly the microviscosity (decreased fluidity) of hepatocyte plasma membranes and altered membrane phospholipid composition. These changes correlated with enhanced insulin binding to isolated membranes. Moreover, in response to insulin, plasma membranes isolated from 'fasted' hepatocytes generated only one half the amount of the second messenger (PDH activator) observed in membranes of fed animals. The amount of PDH activator generated by incubation of plasma membranes with insulin correlated inversely with both insulin binding and membrane microviscosity. We conclude that 1) fasting induces both coupling defect and post-receptor changes in insulin's action; 2) both extracellular and intracellular factors contribute to fasting-induced dissociation of insulin binding from insulin action; 3) insulin/glucagon ratio may influence hepatocyte responsiveness to insulin; 4) alterations in plasma membrane fluidity and phospholipid composition may alter insulin binding and contribute to its dissociation from the subsequent action; 5) membranes isolated from 'fasted' hepatocytes generate less mediator of insulin action than do membranes isolated from 'fed' hepatocytes.

Changes of liver mitochondrial and microsomal phospholipids resulting from chronic exercise and training in rats

The concentration of liver mitochondrial and microsomal phospholipids after 40 days exercise and training in rats was investigated. In both, mitochondrial and microsomal fractions of exercised rats an increase of phosphatidylcholine and a decrease of phosphatidylserine were observed. In liver mitochondria an increase of diphosphatidylglycerol and a decrease of phosphatidylethanolamine in exercised rats were found. In liver microsomes of exercised rats an increase of phosphatidylinositol was found.

Phospholipid composition and metabolism of crustacean gills as related to changes in environmental salinities: relationship between Na+-K+-ATPase activity and phospholipids

The phospholipid composition and metabolism are studied in crustacean gills. It is reported that branchiae are rich in PC, PE and DPG and abundant in long chain polyunsaturated fatty acids (20:4 omega 6 and 20:5 omega 3 acids). The pathways of phospholipids synthesis appear similar to those described for vertebrates. It is demonstrated that there exist significant differences in the level of phosphatides between the anterior and posterior gills of Eriocheir sinensis. No matter what the salinity, the three more posterior located gills of Chinese crabs are shown to contain much more unsaturated phospholipids (PE and DPG). This is particularly true when animals are acclimated to dilute media. Moreover, lipids of posterior gills appear more fluid than the anterior ones as reported by the values of the degree of fluorescence polarization and the index of unsaturation of fatty acids. It is suggested that these lipid changes may indicate the existence of a functional difference between the various branchiae of euryhaline Eriocheir sinensis with respect to their ability to transport salt. It is shown that the renewal of DPG and PS is increased in posterior gills isolated from freshwater Chinese crabs. It is postulated that the enhanced formation of DPG in posterior gills is an indicator of an increased synthesis of mitochondria having as principal function to produce the necessary energy for the Na+ uptake. An attempt is made to correlate the PS metabolism and the Na+-K+-ATPase activity which is particularly located in the mitochondrial fractions of the three pairs of posterior gills.

Effect of 13-cis retinoic acid on fatty acid composition and membrane-associated enzymes in rat submandibular salivary glands

Weanling rats were fed for 4 weeks semipurified diets containing 0, 100 or 300 mg 13-cis retinoic acid per kg diet. The activities of (Na+ + K+)-ATPase, Mg2+-ATPase and gamma-glutamyltranspeptide were measured in submandibular salivary gland (SMSG) homogenates. The activity of (Na+ + K+)-ATPase in the SMSG was reduced in rats fed 13-cis retinoic acid. There was no effect on the activities of the other two enzymes. Fatty acid composition of total lipids in SMSG suggest that decrease in (Na+ + K+)-ATPase activity may be associated with changes in fatty acid composition of total lipids.

Ion transport in hypertension

A wide range of abnormalities of membrane sodium and potassium transport can be demonstrated in patients with essential hypertension, and in rats with genetic hypertension and with some forms of experimental hypertension. In the human red cell increased permeability to sodium and potassium, increased ouabain-sensitive sodium pumping, lithium-sodium counter-transport, and frusemide-sensitive co-transport have been described; by contrast, in the human leucocyte sodium pumping is reduced. In the spontaneously hypertensive rat and the rat with mineralocorticoid-induced hypertension, increased permeability to sodium and potassium, with increased ouabain-sensitive pumping, is shared by the red cell and the arterial smooth muscle. This abnormality is associated with decreased cell-membrane affinity for calcium and increased cell-membrane viscosity. It is proposed that in essential hypertension the decreased membrane affinity for calcium is a primary pathogenetic change giving rise to secondary changes in sodium and potassium transport.

Sulfatide content and (Na+ + K+)-ATPase activity of skin and gill during larval development of the Chilean frog, Calyptocephalella caudiverbera

The sulfatide content, phospholipid concentration, and (Na+ + K+)-ATPase activity from skin and gills of different stages of larval development of Calyptocephalella caudiverbera (a Chilean frog) were analyzed. Additionally, the short-circuit current in skin was studied. When skin and gills, depending on the stage of larval development, present (Na+ + K+)-ATPase activity, they have a high ratio of sulfatide to amount of membrane and the phosphatidylserine concentration remains unchanged. Sulfatide content and (Na+ + K+)-ATPase activity in skin are in direct relationship with the level of sodium flux present during development. The specific enzymatic hydrolysis of sulfatide with partially purified arylsulfatase of pig kidney inhibits 100% of the ouabain-sensitive (Na+ + K+)-ATPase. The ouabain-insensitive ATPase remains virtually unchanged with the treatment, even with a high concentration of arylsulfatase or with ouabain present in the medium. These experiments strongly suggest a role of sulfatides in the (Na+ + K+)-ATPase activity and, as a consequence, in sodium ion transport.

Changes induced by hashish constituents on human erythrocyte phospholipids

The possible effect of delta 9-THC on human erythrocyte phospholipids of chronic hashish users was studied. Changes in individual phospholipids concentrations were observed in heavy hashish users after smoking the drug. Results are discussed in relation to the possible alterations of enzymatic mechanisms which require the presence of essential for their activation phospholipids.

The significance of lymphocyte lipid changes after smoking hashish

The increase of lymphocyte total lipids and phospholipids after smoking hashish, indicates either a lipid transfer from their site of production after smoking the drug or a mobilization of their biosynthetic mechanism in the lymphocyte. A fluctuation of individual phospholipid concentrations after "smoking" is related to the influence of certain hashish compounds on the various biosynthetic pathways of phospholipids in lymphocytes. Changes in phosphatidylcholine, phosphatidylinositol and phosphatidylserine are related to a possible fluctuation of the overall immune ability of the lymphocyte, by affecting the lymphocyte membrane enzyme mechanisms.

The possible effect of hashish on leukocytes and plasma lipids

The possible fluctuation of leukocytes and plasma lipids, 30--60 min after smoking hashish, was studied. Total phospholipid content in both leukocytes and plasma was increased in a similar way to the total lipid content after smoking hashish. Differences in most of the phospholipid classes in leukocytes and plasma before and after smoking hashish were observed while the values in controls and chronic users of the drug before smoking hashish were found to be relatively close. Findings are discussed in relation to the pharmacological action of the drug on liver lipid metabolism.

Role of negatively charged phospholipids in highly purified (Na+ + K+)-ATPase from rabbit kidney outer medulla studies on (Na+ + K+)-activated ATPase, XXXIX

1. The requirement for specific polar head groups of phospholipids for activity of purified (Na+ + K+)ATPase from rabbit kidney outer medulla has been investigated. 2. Comparison of content and composition of phospholipids in microsomes and the purified enzyme indicates that purification leads to an increase in the phospholipid/protein ratio and in phosphatidylserine content. 3. The purified preparation contains 267 molecules phospholipid per molecule (Na+ + K+)-ATPase, viz. 95 phosphatidylcholine, 74 phosphatidylethanolamine, 48 spingomyelin, 35 phosphatidylserine and 15 phosphatidylinositol. 4. Complete conversion of phosphatidylserine into phosphatidylethanolamine by the enzyme phosphatidylserine decarboxylase has no effect on the (Na+ + K+)-ATPase activity of the purified preparation. 5. Complete hydrolysis of phosphatidylinositol by a phospholipase C from Staphylococcus aureus, which is specific for this phospholipid, has no effect on the (Na+ + K+)-ATPase activity. 6. Hydrolysis of 95% of the phosphatidylcholine and 60--70% of the spingomyelin and phosphatidylethanolamine by another phospholipase C (Clostridium welchii) lowers the (Na+ + K+)-ATPase activity by about 20%. 7. Combination of the phospholipid-converting enzymes has the same effect as can be calculated from the effects of the enzymes separately. Only complete conversion of both phosphatidylserine and phosphatidylinositol results in a loss of 44% of the (NA+ + K+)-ATPase activity and 36% of the potassium 4-nitrophenylphosphatase activity. 8. These experiments indicate that there is no absolute requirement for one of the polar head groups, although in the absence of negative charges the activity is lower than in their presence.

Phospholipid composition of Down's syndrome and normal platelets

1. Total and individual phospholipids were quantitated in platelets isolated from normal and Down's syndrome (D.S.) subjects. Phospholipids were extracted from isolated platelets, separated by thin layer chromatography and quantitated by measurement of fluorescence of the compounds using a thin layer chromatogram scanner. The total amount of phospholipid was similar in D.S. and control subjects. The amount and percent composition of phosphatidyl serine, phosphatidyl ethanolamine, phosphatidgl inositol, phosphatidyl choline and sphingomyelin was also similar in D.S. and normal platelets. 2. The studies were undertaken to determine if the decrease in Na+/K+ AtPase activity observed in D.S. platelets was associated with alteration in phospholipid composition. The present report would indicate that no major differences in phospholipid composition are present in D.S. platelets that would account for the observed decrease in Na+/K+ AtPase activity.

The relationship between histamine secretion and 45calcium uptake by mast cells

1. Unstimulated mast cells from the peritoneal cavity of the rat take up (45)Ca: the initial phase of rapid uptake being complete after 1 min incubation of the cells with the isotope. Stimulation of the mast cells with an antigen-antibody reaction, dextran or concanavalin A induces an increase in the uptake of (45)Ca which is accompanied by a release of granular material: this increase in (45)Ca uptake is also complete in 1 min. The majority of the stimulated (45)Ca uptake cannot be explained in terms of binding of Ca to released granular material, or to an enlargement in either the extracellular compartment or the cell surface area.2. The magnitude of the increase in (45)Ca uptake caused by stimulating the mast cells increases when the degree of histamine secretion increases.3. The increased (45)Ca uptake induced by stimulation of the mast cells and the degree of histamine secretion are both dependent on extracellular H ion concentration. Changes of pH cause similar changes in (45)Ca uptake and secretion with maxima at pH 7.5.4. Two thirds of the (45)Ca uptake induced by an antigen-antibody reaction or by the Ca ionophore A 23187 is unaffected by inhibiting glycolysis and oxidative phosphorylation. Histamine secretion on the other hand is practically abolished by this metabolic inhibition. Thus, (45)Ca uptake proceeds in the absence of the discharge of granules.5. Dibutyryl cyclic AMP or theophylline inhibit both the increase in (45)Ca uptake and the histamine secretion caused by stimulating mast cells with an antigen-antibody reaction. Cyclic AMP, cyclic GMP and dibutyryl cyclic GMP have no effect on uptake or secretion.6. The Ca ionophore, A 23187, induces uptake of (45)Ca and histamine secretion, neither effect being inhibited by either dibutyryl cyclic AMP or theophylline.7. Phosphatidyl serine increases both (45)Ca uptake and the histamine release induced by an antigen-antibody reaction, dextran or concanavalin A.