Structure of membrane holes in osmotic and saponin hemolysis

The influence of LTS-4, a saponoside from Lysimachia thyrsiflora L., on human skin fibroblasts and human melanoma cells

We investigated the effect of a triterpene saponoside from Lysimachia thyrsiflora L. upon the viability, proliferation, morphology and cell motility of human melanoma HTB-140 cells and human skin fibroblasts (HSFs). The compound, denoted LTS-4, decreased the viability and rate of cell growth of both cell types in a time-and dose-dependent manner, and proved cytotoxic against cancer cells at significantly lower concentrations than for fibroblasts. LTS-4 also affected the morphology of the examined cells, causing vacuolisation and actin cytoskeleton disintegration, and had an inhibitory effect on the tumour cell motility.

Effects of Quillaja Saponin (Quillaja saponaria) on Early Embryonic Zebrafish (Danio rerio) Development

Although much attention has focused on environmental contamination by heavy metals, pesticides, and polychlorinated biphenyls, potential deleterious effects of naturally occurring organic compounds have received much less consideration. Saponins, which are glycosides found in many plants, are important, environmentally ubiquitous organic compounds. Saponins have both beneficial and deleterious effects in adults, but little is known about how saponins effect early vertebrate embryonic development. The authors tested the toxicity of quillaja saponin using a zebrafish embryo assay. Quillaja saponin, extracted from bark of the tree, Quillaja saponaria, is a common foaming agent used in foods and beverages. At 6 h post fertilization, zebrafish embryos were exposed to five concentrations (0 [negative control], 1, 5, 10 or 20 μg) of quillaja saponin per milliliter of medium. Zebrafish embryos exposed to 2% ethanol were positive controls (100% embryonic death). Embryos were assessed at 30, 54, and 72 h post fertilization for changes in embryonic development, mortality, time of hatching, and morphological deformities. Embryos exposed to 1 and 5 μg saponin were healthy, showed no obvious deformities, but exhibited shrinkage of the chorion. Hatching time for zebrafish embryos exposed to 1 and 5 μg/ml saponin decreased by 18 h compared to unexposed embryos. Zebrafish embryos treated with 5 μg/ml saponin responded less to touch than embryos treated with 1 μg/ml saponin or controls. Zebrafish embryos exposed to more than 5 μg/ml saponin exhibited 100% embryonic mortality. These results indicate that exposure to 5 μg/ml or less of quillaja saponin acts as a growth promoter, whereas concentrations of 10 μg/ml or greater are lethal.

Psychosis pathways converge via D2high dopamine receptors

The objective of this review is to identify a target or biomarker of altered neurochemical sensitivity that is common to the many animal models of human psychoses associated with street drugs, brain injury, steroid use, birth injury, and gene alterations. Psychosis in humans can be caused by amphetamine, phencyclidine, steroids, ethanol, and brain lesions such as hippocampal, cortical, and entorhinal lesions. Strikingly, all of these drugs and lesions in rats lead to dopamine supersensitivity and increase the high-affinity states of dopamine D2 receptors, or D2High, by 200-400% in striata. Similar supersensitivity and D2High elevations occur in rats born by Caesarian section and in rats treated with corticosterone or antipsychotics such as reserpine, risperidone, haloperidol, olanzapine, quetiapine, and clozapine, with the latter two inducing elevated D2High states less than that caused by haloperidol or olanzapine. Mice born with gene knockouts of some possible schizophrenia susceptibility genes are dopamine supersensitive, and their striata reveal markedly elevated D2High states; suchgenes include dopamine-beta-hydroxylase, dopamine D4 receptors, G protein receptor kinase 6, tyrosine hydroxylase, catechol-O-methyltransferase, the trace amine-1 receptor, regulator of G protein signaling RGS9, and the RIIbeta form of cAMP-dependent protein kinase (PKA). Striata from mice that are not dopamine supersensitive did not reveal elevated D2High states; these include mice with knockouts of adenosine A2A receptors, glycogen synthase kinase GSK3beta, metabotropic glutamate receptor 5, dopamine D1 or D3 receptors, histamine H1, H2, or H3 receptors, and rats treated with ketanserin or aD1 antagonist. The evidence suggests that there are multiple pathways that convergetoelevate the D2High state in brain regions and that this elevation may elicit psychosis. This proposition is supported by the dopamine supersensitivity that is a common feature of schizophrenia and that also occurs in many types of genetically altered, drug-altered, and lesion-altered animals. Dopamine supersensitivity, in turn, correlates with D2High states. The finding that all antipsychotics, traditional and recent ones, act on D2High dopamine receptors further supports the proposition.

Method for monitoring of mitochondrial cytochrome c release during cell death: Immunodetection of cytochrome c by flow cytometry after selective permeabilization of the plasma membrane

BACKGROUND

Cytochrome c release from mitochondria to cytosol is a hallmark of apoptosis and is used to characterize the mitochondria-dependent pathway of this type of cell death. Techniques currently used to measure cytochrome c release, Western blot and fluorescence microscopy of immunolabeled cells, are time-consuming and inaccurate, and the latter is still limited by sample size.

METHODS

We developed a rapid and reliable technique to detect cytochrome c release during drug-induced apoptosis, using flow cytometry. Plasma membrane of apoptotic HL-60 cells and thymocytes, treated with staurosporine and dexamethasone, respectively, were selectively permeabilized by digitonin at a low concentration. The released cytochrome c was quickly washed out from cells and that which remained in the mitochondria was immunolabeled after fixing the cells.

RESULTS

The fraction of cells that retained their mitochondrial cytochrome c, or the highly fluorescent cells, gradually decreased so that after 4-8 h of drug treatment almost all the cells lost their cytochrome c and emerged as a population of low fluorescent cells. This was confirmed by parallel fluorescence microscopy of cells immunolabeled for cytochrome c.

CONCLUSIONS

This technique allows the analysis of cytochrome c release from mitochondria of a large number of apoptotic cells in a short period of time and is proposed as an alternative to the methods currently used for this same purpose.

Osmotic swelling and hole formation in membranes of thalassemic and spherocytic erythrocytes

Osmotic swelling and kinetics of the pore formation in the membranes of spherocytic, thalassemic, and normal erythrocytes were studied by measuring the time-dependent capacitance and conductance at a frequency of 0.2 MHz. No significant difference between the swelling rate of control and spherocytic cells was observed, whereas slower kinetics of swelling were found for thalassemic cells. Time records of the conductance indicate that the probability of the pore formation in the stretched membrances varies in the following order: thalassemia < control < spherocytosis. Based on these findings it was concluded that the erythrocyte swelling is controlled by the initial cell shape, volume, intracellular hemoglobin concentration, and elastic membrane properties, whereas the kinetics of the pore formation depend solely on the resistivity of the stretched membrane of the swollen RBC to the osmotic shock. Therefore, it was assumed that investigations of the pore formation may be used not only for examinations of spherocytic and thalassemic cells, but also for normocytic, normochromic, biconcave-shaped RBCs with altered membrane elasticity.

The biological action of saponins in animal systems: a review

Saponins are steroid or triterpenoid glycosides, common in a large number of plants and plant products that are important in human and animal nutrition. Several biological effects have been ascribed to saponins. Extensive research has been carried out into the membrane-permeabilising, immunostimulant, hypocholesterolaemic and anticarcinogenic properties of saponins and they have also been found to significantly affect growth, feed intake and reproduction in animals. These structurally diverse compounds have also been observed to kill protozoans and molluscs, to be antioxidants, to impair the digestion of protein and the uptake of vitamins and minerals in the gut, to cause hypoglycaemia, and to act as antifungal and antiviral agents. These compounds can thus affect animals in a host of different ways both positive and negative.

Kinetics of erythrocyte swelling and membrane hole formation in hypotonic media

Red blood cell (RBC) swelling and membrane hole formation in hypotonic external media were studied by measuring the time-dependent capacitance, C, and the conductance, G, in the beginning of the beta-dispersion range. At high and moderate osmolarities of the external solution the capacitance reaches a steady-state whereas at low osmolarities it reveals a biphasic kinetics. Examination of RBC suspensions exposed to different concentrations of HgCl(2) demonstrates that water transport through mercury-sensitive water channel controls RBC swelling. Unlike the capacitance, an increase in the conductance to a stationary level is observed after a certain delay. A comparison of G(t) curves recorded for the suspensions of the intact cells and those treated with cytochalasin B or glutaraldehyde demonstrates the significant effect of the membrane viscoelasticity on the pore formation. It is shown that the stretched membrane of completely swollen RBC retains its integrity for a certain time, termed as the membrane lifetime, t(memb). Therefore, the resistivity of RBCs to a certain osmotic shock may be quantified by the distribution function of RBC(t(memb)).

The sterol composition of Trypanosoma cruzi changes after growth in different culture media and results in different sensitivity to digitonin-permeabilization

Respiration, oxidative phosphorylation. and the corresponding changes in membrane potential (deltapsi) of Trypanosoma cruzi epimastigotes grown either in liver infusion-tryptose (LIT) or brain heart infusion (BHI) culture medium were assayed in situ using digitonin to render their plasma membrane permeable to succinate, ADP, safranine O, and other small molecules. When the cells were permeabilized with 64 microM digitonin, a concentration previously used with epimastigotes, the ability of the cells grown in LIT medium to sustain oxidative phosphorylation was demonstrated by the detection of an oligomycin-sensitive decrease in mitochondrial membrane potential induced by ADP. In contrast, the cells grown in BHI medium were not able to sustain a stable membrane potential and did not respond to ADP addition. Analyses of oxygen consumption by these permeabilized cells indicated that the rate of basal respiration, which was similar in both cell types, was significantly decreased by 64 microM digitonin. Addition of ADP to the permeabilized cells grown in LIT medium promoted an oligomycin-sensitive transition from resting to phosphorylating respiration in contrast to the cells grown in BHI medium, whose respiration decreased steadily and did not respond either to ADP or CCCP. Titration of the cells grown in BHI medium with different digitonin concentrations indicated that their mitochondria have higher sensitivity to digitonin than those grown in LIT medium. Analysis of the sterol composition of epimastigotes grown in the two different media showed a higher percentage of cholesterol in total and mitochondrial extracts of epimastigotes grown in BHI medium as compared to those grown in LIT medium, suggesting the involvement of this sterol in their increased sensitivity to digitonin-permeabilization.

Effects of Quillaja saponins on growth, metabolism, egg production and muscle cholesterol in individually reared Nile tilapia (Oreochromis niloticus)

The effects of supplementation of a Quillaja saponin (QS) mixture in the diets of tilapia have been studied using a respirometer system that allowed feeding and continuous measurement of oxygen consumption of individual fish. Five fish each were given control diet (C group) and control diet supplemented with 150 mg kg(-1) (S150 group) or 300 mg kg(-1) (S300 group) QS. At the end of 14 weeks the weight gain of the S300 group was significantly higher than control (P<0.05) whereas that of the S150 group had an intermediate value. The S150 group had a higher growth rate (P=0.05) after the first 3 weeks of feeding with the experimental diets, compared to the other two groups. At the end of the experiment the S300 group had significantly higher (P<0.05) average values for energy retention, apparent lipid conversion, carcass fat, energy and significantly lower (P<0.05) average values for apparently unutilised energy and carcass ash content compared to the C group. The corresponding values of the S150 group were intermediate between the C and S300 groups. One out of two female fish in the S150 group and both female fish in the S300 group never produced eggs during the entire 14-week experimental period. Contrarily, all three female fish in the control group and one out of the two female fish in the S150 group regularly produced eggs, at a rate of approximately once in every 14 days. The muscle cholesterol level in the S300 group was significantly higher than that of the C group. Possible mechanisms of action of the dietary saponins are discussed.

Membrane transport in the malaria-infected erythrocyte

The malaria parasite is a unicellular eukaryotic organism which, during the course of its complex life cycle, invades the red blood cells of its vertebrate host. As it grows and multiplies within its host blood cell, the parasite modifies the membrane permeability and cytosolic composition of the host cell. The intracellular parasite is enclosed within a so-called parasitophorous vacuolar membrane, tubular extensions of which radiate out into the host cell compartment. Like all eukaryote cells, the parasite has at its surface a plasma membrane, as well as having a variety of internal membrane-bound organelles that perform a range of functions. This review focuses on the transport properties of the different membranes of the malaria-infected erythrocyte, as well as on the role played by the various membrane transport systems in the uptake of solutes from the extracellular medium, the disposal of metabolic wastes, and the origin and maintenance of electrochemical ion gradients. Such systems are of considerable interest from the point of view of antimalarial chemotherapy, both as drug targets in their own right and as routes for targeting cytotoxic agents into the intracellular parasite.

Elasticity of the red cell membrane and its relation to hemolytic disorders: an optical tweezers study

We have used optical tweezers to study the elasticity of red cell membranes; force was applied to a bead attached to a permeabilized spherical ghost and the force-extension relation was obtained from the response of a second bead bound at a diametrically opposite position. Interruption of the skeletal network by dissociation of spectrin tetramers or extraction of the actin junctions engendered a fourfold reduction in stiffness at low applied force, but only a twofold change at larger extensions. Proteolytic scission of the ankyrin, which links the membrane skeleton to the integral membrane protein, band 3, induced a similar effect. The modified, unlike the native membranes, showed plastic relaxation under a prolonged stretch. Flaccid giant liposomes showed no measurable elasticity. Our observations indicate that the elastic character is at least as much a consequence of the attachment of spectrin as of a continuous membrane-bound network, and they offer a rationale for formation of elliptocytes in genetic conditions associated with membrane-skeletal perturbations. The theory of Parker and Winlove for elastic deformation of axisymmetric shells (accompanying paper) allows us to determine the function BH(2) for the spherical saponin-permeabilized ghost membranes (where B is the bending modulus and H the shear modulus); taking the literature value of 2 x 10(-19) Nm for B, H then emerges as 2 x 10(-6) Nm(-1). This is an order of magnitude higher than the value reported for intact cells from micropipette aspiration. Reasons for the difference are discussed.

Fungal resistance to plant antibiotics as a mechanism of pathogenesis

Many plants produce low-molecular-weight compounds which inhibit the growth of phytopathogenic fungi in vitro. These compounds may be preformed inhibitors that are present constitutively in healthy plants (also known as phytoanticipins), or they may be synthesized in response to pathogen attack (phytoalexins). Successful pathogens must be able to circumvent or overcome these antifungal defenses, and this review focuses on the significance of fungal resistance to plant antibiotics as a mechanism of pathogenesis. There is increasing evidence that resistance of fungal pathogens to plant antibiotics can be important for pathogenicity, at least for some fungus-plant interactions. This evidence has emerged largely from studies of fungal degradative enzymes and also from experiments in which plants with altered levels of antifungal secondary metabolites were generated. Whereas the emphasis to date has been on degradative mechanisms of resistance of phytopathogenic fungi to antifungal secondary metabolites, in the future we are likely to see a rapid expansion in our knowledge of alternative mechanisms of resistance. These may include membrane efflux systems of the kind associated with multidrug resistance and innate resistance due to insensitivity of the target site. The manipulation of plant biosynthetic pathways to give altered antibiotic profiles will also be valuable in telling us more about the significance of antifungal secondary metabolites for plant defense and clearly has great potential for enhancing disease resistance for commercial purposes.

Effect of soybean saponins and gypsophila saponin on morphology of colon carcinoma cells in culture

The effect of saponins on colonic epithelial carcinoma cell (HCT-15) morphology was studied. Cells in culture were incubated with different concentrations of soybean saponins (SS) or gypsophila saponin (GS) for 24 hr. Scanning electron microscopy revealed a very rough and granular cell surface in cells treated with the lowest concentration of GS (40 ppm). Minor morphological changes were observed in the cell surface of soybean saponin-treated cells at a concentration of 1200 ppm. Examination by transmission electron microscopy indicated a dose-dependent effect of saponins on intracellular morphology of colonic epithelial carcinoma cells. Cells treated with 600 ppm or more of soybean saponins developed numerous cytoplasmic vesicles, had decreased density of cytoplasmic material and demonstrated deformations in plasma and nuclear membranes. Gypsophila saponin at a concentration of 40 ppm produced few changes in intracellular and membrane structure, whereas 80 ppm saponin induced the formation of vesicles. However, at both concentrations, changes in the density of cytoplasmic material was less extensive than in soybean saponin-treated cells. The highest concentration of gypsophila saponin used (160 ppm) completely destroyed the plasma membrane. These results indicate that soybean saponins and gypsophila saponin interact with cell membranes and induce significant dose-dependent cell morphological changes; however, they appear to act through different mechanisms.

Detection of Staphylococci in mouse phagocytic cells by in situ hybridization using biotinylated DNA probes

In situ hybridization was used to detect intracellular Staphylococcus aureus and S. epidermidis in mouse phagocytic cells after experimental infection of C3H mice with Staphylococci via abdominal or intravenous injection. Isolated ascites or whole blood were tested by the phagocyte smear technique, using bacteriolytic enzymes to preserve phagocytic cell morphology. The exposed bacterial DNA was visualized as intracellular hybridized signals by use of biotinylated DNA probes and by immunocytochemistry using streptavidin-alkaline phosphatase conjugates as detector molecules. These DNA probes, prepared from randomly cloned genomic DNA fragments of S. aureus and S. epidermidis, were strain-specific and did not cross-hybridize either in situ or on dot-blot hybridization. This technique of in situ hybridization with phagocyte smears is useful for detection and diagnosis of intracellular bacteria regardless of viability.

Effect of specific membrane perturbations on alpha 1-adrenergic and muscarinic-cholinergic signal transduction in rat parotid cell aggregates

Alpha 1-adrenergic and muscarinic-cholinergic stimulated IP3 production and calcium mobilization are inhibited by treatment of parotid cell aggregates with methanol, hydrogen peroxide and saponin. Only methanol exerts an effect on binding to receptors. In most cases a close correspondence exists between inhibition of alpha 1-adrenergic and muscarini-cholinergic responses as well as inhibition of IP3 production and calcium mobilization. G-protein dependent signal transduction, therefore appears to be quite sensitive to plasma membrane perturbation and membrane active agents may provide useful tools for elucidation of transduction mechanisms and their regulation.

Similar effects of saponin treatment and aging on coupling of alpha 1-adrenergic receptor-G-protein

The effects of the nonionic detergent saponin on alpha 1-adrenergic signal transduction were investigated using rat parotid cells and membrane preparations. Fifty microM epinephrine-stimulated 45Ca2+ efflux and inositol 1,4,5-triphosphate (Ins[1,4,5]P3) production in adult parotid cells were significantly decreased after saponin treatment. Saponin did not alter the concentration of alpha 1-adrenergic receptors labeled by [3H]prazosin, but significantly reduced the guanosine imido diphosphate (GppNHp)-induced shift from high to low affinity sites. Fifty microM epinephrine-stimulated high affinity GTPase activity was also reduced by saponin treatment. These data suggest that reduced alpha 1-adrenergic receptor-stimulated functional responsiveness following saponin treatment may be due to impaired uncoupling of receptor-G-protein complexes.

Digitonin-aided loading of Fluo-3 into embryogenic plant cells

This paper describes a method to load embryogenic plant cells with Fluo-3 in its cell impermeant form with the aid of digitonin. Attempts to load cells with Fluo-3/AM were all unsuccessful. Presumably the indicator is cleaved outside the cells and cannot penetrate in its acidic form. At a low pH, Fluo-3 enters the plant cells but normal Ca2+ homeostasis seems to be disturbed. Successful loading of Fluo-3 was achieved by adding 0.1% digitonin during incubation with the Ca(2+)-indicator. A bright fluorescence was observed in the epidermal layer of heart and torpedo shaped somatic embryos of carrot with confocal scanning laser microscopy. Vacuoles were always without fluorescence which indicates that the dye, after loading, remains in the cytosol and does not leak out. The fluorescence intensity was sensitive to treatments with A23187 and EGTA. We conclude that Fluo-3 can be effectively loaded, with the aid of digitonin, into plant embryogenic cells in liquid culture. Therefore, we expect this technique to be very useful for the study of changes in cytosolic free Ca2+ levels during plant growth and development.

Simultaneous measurement of cell surface and intracellular antigens by multiple flow cytometry

We have employed a method for permeabilizing lymphocytes with the detergent saponin in order to detect an intracellular protein simultaneously with surface antigens by flow cytometry (FCM). Using monoclonal antibodies specific for the murine CD2 receptor and for the lysosomal enzyme, beta-glucuronidase (Gus), we found that the expression of both of these antigens increased markedly when T cells were activated. Two sensitive methods were used to show that FCM provided an accurate measure of the actual number of CD2 and Gus molecules present in the lymphocytes. Immunogold electron microscopy revealed the precise ultrastructural localization of these different components and corroborated the specificity of the multiple labelling procedure for the simultaneous detection of surface and intracellular antigens. We also developed a three-colour FCM technique which we used to examine the changes in Gus expression in the CD4 and CD8 T cell sub-sets during activation.

A flow cytometric technique for simultaneous analysis of human mononuclear cell surface antigens and DNA

A method for dual staining of mononuclear cells for lymphocyte phenotypic markers and DNA is described. The cells were stained with fluorescein-conjugated monoclonal antibodies and then rendered permeable to propidium iodide using saponin. Propidium iodide stains DNA and, using flow cytometry, cell cycle analysis of individual lymphocyte subpopulations can be determined. Saponin acts within 1 min, preserves expression of surface antigens and is effective at all concentrations from 0.001% to 1%. This technique is simple, rapid and gives reproducible results.

Calmodulin loss in vascular smooth muscle following Triton X-100 or saponin skinning

The calmodulin (CaM) content of intact and chemically skinned strips of rat caudal artery was measured using a 125I-CaM radioimmunoassay. The total CaM measured following homogenization of arterial tissue with EGTA and EGTA/Triton X-100 was 2.58 mumol/kg wet tissue. Based on a smooth muscle volume of 40%, this value corresponds to a cellular CaM concentration of 6.5 microM. Approximately 97% of total CaM was soluble and approximately 3% was EGTA-nonextractable. Permeabilization of the plasmalemma with 0.15 mg/ml saponin or 0.5% Triton X-100 caused significant detergent-dependent loss of CaM. At the end of a 1 h skinning period, tissues exposed to saponin lost 30% of total CaM. By comparison, tissues skinned under the same conditions with Triton X-100 lost 50%. During a subsequent 4 h exposure to relaxing solution, total tissue CaM continued to decline. The exponential loss over the 5 h period was described by a first order model having diffusible and nondiffusible CaM components. The diffusible CaM component of saponin skinned tissue (59%) was significantly less than the diffusible component of those skinned with Triton X-100 (88%); however, the rate coefficients for CaM diffusion (0.78 h-1 and 0.91 h-1, respectively) did not statistically differ. The nondiffusible component of CaM was significantly larger in saponin treated strips (42%) than in Triton X-100 permeabilized tissue (12%). Arterial strips skinned with Triton X-100, which were subsequently exposed to relaxing solution for up to 22 h, lost significantly more CaM than those retained in Triton X-100 skinning solution for a comparable duration.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunoperoxidase methods for the localization of antigens in cultured cells and tissue sections by electron microscopy

We have presented our detailed methods for localizing antigens in cultured cells and tissue sections by IP at the EM level. Immunoperoxidase cytochemistry is particularly well suited for the study of sparse antigens as a result of the enzymatic amplification afforded by the method, and of molecules confined within a membrane-enclosed compartment wherein the DAB reaction produce can accumulate. Although IP is commonly used to localize membrane-compartmentalized molecules, reliable qualitative information can also be obtained on cytoplasmic antigens as well (Anderson et al., 1978; Merisko et al., 1986; Rodman et al., 1984). For these and other reasons, it is likely that IP cytochemistry will continue to be an important tool for the cell biologist especially in the study of membrane traffic. Other inventive combinations of immunocytochemical methods will likely be forthcoming, for example, combining IP localization with postembedding labeling by colloidal-gold conjugates to provide triple EM labeling.

Comparative effects of sugars on the hemolytic activity of Schistosoma mansoni and other hemolytic agents

1. The rate of red blood cell lysis by the hemolytic agent in adult worm homogenates of Schistosoma mansoni is slowed in the presence of added sugars (50 mM). 2. Trisaccharides were the most effective in slowing and reducing lysis. Disaccharides were more effective than monosaccharides. 3. The addition of sodium, potassium or lithium chloride salts (25 mM) stimulated hemolysis by the S. mansoni agent. 4. Hemolysins with known mechanisms were tested to determine the effects of added sugars (50 mM) or salts (25 mM). 5. The S. mansoni hemolytic agent responds to the addition of sugars and salts in a manner similar to small membrane pore formers.

Differential permeabilization of membranes by saponin treatment of isolated rat hepatocytes. Release of secretory proteins

Monolayer cultures of rat hepatocytes were treated with increasing concentrations of saponin (prepared from Gypsophila plants) for 30 min at 6 degrees C. Differential permeabilization of the intracellular membranes could be demonstrated: at 0.040 mg of saponin/ml the plasma membrane was permeabilized, as assessed by the release of 50% of the total cellular amount of lactate dehydrogenase, and at 0.20 mg/ml the endoplasmic reticulum was permeabilized, as measured by the release of 50% of pulse-35S-labelled albumin. The Golgi complex was permeabilized at an intermediate saponin concentration, as indicated by the release of homogeneously 35S-labelled albumin; about half the intracellular albumin is located in this organelle. At 1.0 up to 5.0 mg of saponin/ml 90-95% of the radioactively labelled albumin was released. Even at 5.0 mg/ml less than 10% of the membrane of the endoplasmic reticulum was solubilized, as judged by the degree of release of a membrane-bound enzyme specific for this organelle. These results demonstrate the usefulness of saponin as a tool for investigating the interior of different intracellular compartments.

Use of pre-embedding ultrastructural immunocytochemistry in the localization of a secretory product and membrane proteins in cultured prolactin cells

A pre-embedding immunoperoxidase procedure performed directly on cultured cells in situ was used to localize several intracellular antigens at the electron-microscope level. With this procedure, we compared the effect of various fixatives, with or without saponin permeabilization, on the immunoreactivity of a secretory product (prolactin) and membrane proteins in cultured prolactin cells. Prolactin was detected within all compartments of its intracellular secretory pathway. Membrane antigens of the rough endoplasmic reticulum, the Golgi apparatus, and lysosomes were localized in distinct intracellular compartments. These immunocytochemical results are discussed in relationship to others in the literature that describe the localization of similar types of antigens. The technique, here described, which preserves ultrastructural detail and antigenicity, should be applicable for the localization of other intracellular antigens in cultured cells.

Effects of purified ginseng saponins on multilamellar liposomes

To elucidate the mode of interaction between purified ginseng saponins and liposomes, the effects of ginseng saponins at concentrations below and above their critical micelle concentration on the osmotic behavior of liposomes were observed. Liposomes composed of egg phosphatidylcholine (PC), phosphatidic acid (PA) and/or cholesterol (Ch) behave as an ideal osmometer and this activity was described by the linear relationship between (1/A450)3/2 and Cin/Cout. Total saponin prepared from the lateral roots of ginseng cultivated in Korea interacted with multilamellar liposomes and prevented them from behaving as an ideal osmometer. 20-S-Protopanaxadiol saponin showed similar activity but 20-s-protopanaxatriol saponin had weak activity. Ginsenoside Rb1 whose genin is 20-S-protopanaxadiol, disturbed osmotic behavior of Ch-free liposomes but not Ch-containing liposomes as monomers and lyzed both liposomes as micelles. Rg1 whose genin is 20-S-protopanaxatriol, showed no activity on liposomes with or without Ch. It can be suggested that ginseng saponins may interact with and destroy liposomal membranes and that structure of sugar moiety is an important factor to their activities. Ch is not a target in this interaction but suppresses the activity of ginseng saponins.

Intracellular levels and distribution of Ca2+ in digitonin-permeabilized cells

Digitonin and other saponins can be used to selectively permeabilize the plasma membrane of a wide variety of cells without significantly affecting the gross structure and function of Ca2+-sequestering organelles such as mitochondria and endoplasmic reticulum. These characteristics have allowed digitonin to be used in the determination of the intracellular levels and distribution of Ca2+, as well as the measurement of Ca2+ fluxes by organelles "in situ". Studies conducted with several different types of digitonin-permeabilized cells indicate that the endoplasmic reticulum functions as a high affinity and low-capacity intracellular Ca2+ buffer, whereas mitochondria operate as a relatively low affinity but high capacity Ca2+ buffering system. However, recent findings suggest that mitochondria have a comparable affinity for net Ca2+ uptake in the presence of physiological concentrations of polyamines. The use of permeabilized cells has also been important in the identification of the endoplasmic reticulum as a site at which the recently discovered second messenger inositol trisphosphate acts to bring about an increase in the cytosolic free Ca2+ concentration. Thus, the selective permeabilization of cells with digitonin and its analogues has been a powerful yet simple tool in the study of intracellular Ca2+ homeostasis.

Interaction of saponin and digitonin with black lipid membranes and lipid monolayers

The effects of the plant glycosides saponin as well as digitonin on the electrical conductance of black lipid membranes and the effect of these agents on the surface pressure of lipid monofilms was investigated. Both saponin and digitonin induced channel-like fluctuations in planar bilayers made either of diphytanoylphosphatidylcholine ( DPhPC ) or of DPhPC and cholesterol 2: 1 (w/w). In cholesterol-free bilayers the amount needed to induce an increase in conductance was 0.3-1 mg/ml for saponin and about 0.2 mg/ml for digitonin. In contrast, in cholesterol-containing bilayers the concentration needed to induce pores was about 10 micrograms/ml for both saponin and digitonin. In cholesterol-containing membranes the fluctuating pores induced by saponin were about 3-times more permeable to K+ than to Cl- and the macroscopic current showed an ohmic behaviour. Surface pressure experiments demonstrate that both glycosides could penetrate into lipid monofilms of pure DPhPC spread at the air/water interface with an initial surface pressure of 30 mN/m. The increase in surface pressure was considerably enhanced in cholesterol-containing films. It is assumed that the channel-like fluctuations induced by saponin as well as digitonin, in both cholesterol-free and cholesterol-rich bilayers are due to the formation of micellar structures within the lipid lattice. Probably the penetration of the glycosides into the lipid bilayer is considerably enhanced by the presence of cholesterol.

The size of erythrocyte ghosts

The volume of resealed erythrocyte ghosts formed during hypotonic hemolysis of normal human erythrocytes was measured by means of a continuous mean corpuscular volume analyzer. The final volume of resealed ghosts was 140.6 +/- 15.2 fl. Strong correlations exist between the volume of ghosts and the initial mean corpuscular volume and mean corpuscular hemoglobin of the erythrocyte, and between the enlargement ratio and the mean corpuscular volume or mean corpuscular hemoglobin of the erythrocyte.

Enzyme release from isolated erythrocytes and lymphocytes in Duchenne muscular dystrophy

The release of lactate dehydrogenase (LDH) was studied in erythrocytes and lymphocytes from patients with Duchenne muscular dystrophy. Erythrocytes were incubated in Krebs-Ringer with or without 30 mM adenosine and in autologous plasma. There was little release of enzyme in Krebs-Ringer solutions up to 24 h or in autologous plasma up to 48 h, with no statistical difference between Duchenne patients and controls. Addition of 30 mM adenosine reduced the release of LDH in Duchenne erythrocytes at 48 h from 32.4 +/- 5.66% (SE) to 6.2 +/- 1.76% (P < 0.05) and in controls from 38.1 +/- 5.93% to 23.5 +/- 4.63% (n.s.). Lymphocytes incubated in Krebs-Ringer containing 33 mM glucose released LDH faster than Duchenne patients and controls. The adenosine effect could be due to abnormal adenosine uptake (because of a generalized membrane defect) or indicate intrinsic differences in the adenine nucleotide metabolism.

The ultrastructural organization of the contractile peripheral protein layer of the human erythroycte membrane

Erythroycte ghosts fixed in glutaraldehyde were dehydrated in (a) alcohol or acetone, (b) propylene glycol followed by Epon and embedded in an epoxy resin. A water-soluble urea/glutaraldehyde mixture was also used. The aim was to study the structure of the peripheral protein layer, which contains spectrin and actin, in the absence of OsO4 induced denaturation changes. Ghost membranes prepared in this way had an asymmetrical quadrilaminar structure. A layer of amorphous peripheral protein +/- 18 nm in width covered the entire inner face of the membrane in the form of a coarse meshwork in both Wash I (haemoglobin-containing) and haemoglobin-free ghosts. Cations (Mg2+ or Ca2+, or Mg2+ plus ATP) had no apparent effect on its fine structure. In contrast, the corresponding layer in OsO4-fixed membranes was represented by scanty, fuzzy material attached to the unit membrane only at irregular intervals. The results demonstrate the superior ability of glutaraldehyde to preserve the peripheral protein layer in thin sections, and afford further support for the view that much of this protein normally exists in an unpolymerized state.

The susceptibility of cholesterol-depleted erythrocytes to saponin and sapogenin hemolysis

The assumption that complex formation between erythrocyte membrane cholesterol and saponins or sapogenins is the cause for their hemolytic activity, was tested by measuring the susceptibility of cholesterol-depleted erythrocytes towards these hemolysins. For some of the hemolysins cholesterol depletion caused inhibition of hemolysis, for others an augmentation. The results suggest that cholesterol does not serve as a specific binding site for these hemolysins.

The use of detergents and immunoperoxidase reagents for the ultrastructural demonstration of internal immunoglobulin in lymph cells

Lymph-borne immunoblasts were fixed in dilute glutaraldehyde and then treated with saponin. This treatment made most parts of the cells permeable to ferritin, so that anti-immunoglobulin (Ig) antibodies which had been conjugated to horse radish peroxidase (HRP) had no difficulty in gaining access to Ig which thus could be demonstrated at an ultrastructural level. Best results were obtained by fixing the cells in 0.1% glutaraldehyde for 7 min and then treating them with a 1% solution of saponin for 100 min at 55 degrees C before exposing them to the Ig-HRP conjugate. The method yielded reproducible results and although it causes a small amount of ultrastructural damage, it may be of value in detecting a variety of intracellular antigens.

Alteration by cereolysin of the structure of cholesterol-containing membranes

When erythrocyte membranes were treated with cereolysin, negatively stained and examined by electron microscopy, ring and arc-shaped structures were observed in the membrane. The outside diameter of the rings varied from 33 to 50 nm with a border thickness of 6.7 to 8.3 nm. The arcs varied in length from 33 to 170 nm with a border thickness of also 6.7 to 8.3 min. When right-side-out erythrocyte ghosts which had been treated with cereolysin were examined by electron microscopy after freeze-fracture, structures with a diameter of 31 to 63 nm were seen in the fracture face of the exoplasmic half of the membrane, but no alterations were visible in the fracture face of the protoplasmic half of the membrane bilayer. Thus the ring structures did not appear to form holes through the membrane. At cereolysin concentrations above 6 microgram/ml rings and arcs were seen when purified toxin alone was examined. At or below 6 microgram/ml toxin rings and arcs were seen only if toxin was incubated with free or membrane-bound cholesterol. Our interpretation is that cereolysin tends to aggregate into ring and arc-shaped structures, and that the tendency to aggregate is increased by cholesterol. Rings and arcs were not seen when erythrocyte ghosts were treated with low, but lytic amounts of cereolysin that significantly altered the premeability of the ghosts.

Secretion granules of the rabbit parotid. Selective removal of secretory contaminants from granule membranes

A membrane subfraction obtained from secretion granules isolated from rabbit parotid has been shown to be contaminated by residual secretory proteins to an estimated level of 25-30% of its total protein. In the present study an additional contaminant has been identified by improved mixing experiments and by comparative peptide mapping of specific polypeptides recovered from gels of membrane and content subfractions. This contaminant coelectrophoresis with (and probably comprises the bulk of) the majority component of the membrane subfraction (mol wt approximately 40,000). The contaminating polypeptides can be removed to a large extent by treating the membranes with low concentrations of saponin in the presence of 0.3 M Na2SO4. Although this treatment disrupts the typical bilayer structure of the granule membrane, it does not appear to cause dissociation of its phospholipids or bona fide membrane proteins.

The sub-membrane reticulum of the human erythrocyte: a scanning electron microscope study

A web-like reticulum underlying the human erythrocyte membrane was studied at a resolution of 5-10 nm by means of scanning electron microscope. The network was visualized in isolated membranes (ghosts) torn open to reveal their interior space and in residues derived from ghosts extracted with Triton X-100. It formed a continuous (rather than patchy) cover over the entire cytoplasmic surface, except where lifted off or torn away. Filaments (5-40 nm in diameter), annular figures (40-60 nm in diameter), and nodes (30-100 nm in diameter) were prominent in different networks. The dimensions of the filaments and the interstices in the reticulum varied with conditions, suggesting that the network has elastic properties. This reticulum is probably related to the erythrocyte membrane proteins spectrin and actin.