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PubMed1959

The origin and fate of annulate lamellae in maturing sand dollar eggs.

Electron micrograph evidence is presented that the nuclear envelope of the mature ovum of Dendraster excentricus is implicated in a proliferation of what appear as nuclear envelope replicas in the cytoplasm. The proliferation is associated with intranuclear vesicles which apparently coalesce to form comparatively simple replicas of the nuclear envelope closely applied to the inside of the nuclear envelope. The envelope itself may become disorganized at the time when fully formed annulate lamellae appear on the cytoplasmic side and parallel with it. The concept of interconvertibility of general cytoplasmic vesicles with most of the membrane systems of the cytoplasm is presented. The structure of the annuli in the annulate lamellae is shown to include small spheres or vesicles of variable size embedded in a dense matrix. Dense particles which are about 150 A in diameter are often found closely associated with annulate lamellae in the cytoplasm. Similar structures in other echinoderm eggs are basophilic. In this species, unlike other published examples, the association apparently takes place in the cytoplasm only after the lamellae have separated from the nucleus. If 150 A particles are synthesized by annulate lamellae, as their close physical relationship suggests, then in this species at least the necessary synthetic mechanisms and specificity must reside in the structure of annulate lamellae.

Animals↗
PubMed1987

Cell membrane fluidity in chronic lymphocytic leukemia (CLL) lymphocytes and its relation to membrane receptor expression.

Cell membrane fluidity (CMF), Ig receptor expression and ecto-ATPase activity were investigated in lymphocytes from patients with chronic lymphocytic leukemia (CLL) and from healthy controls. Significant differences were observed in the parameters of individual CLL cases as compared to normal controls. These findings suggest that malignant transformation of lymphocytes to CLL cells is accompanied by disturbances in cell membrane structure and function, which can be modulated to some extent by exogenous influences on the lipid composition of the cell membrane. The results also suggest, however, that CLL is apparently an inhomogeneous disease with major variations in the investigated parameters among individual cases.

Adenosine Triphosphatases↗
PubMed1989

Erythropoietin. Receptor characteristics during the ontogeny of hamster yolk sac erythroid cells.

Erythropoietin (Epo) binds specifically to receptors on the surface membrane of responsive erythroid cells. In search of ontogenic changes in Epo receptor behavior, we studied characteristics of specific binding to hamster yolk sac erythroid cells during hamster ontogeny. We detected receptors specific for Epo on these cells throughout the duration of their intravascular existence (hamster gestational days 8 through 13). These receptors are saturable at an Epo concentration of 1.2 nM in the incubation medium. Attainment of equilibrium of binding prior to hormone internalization, a requirement for receptor binding assays, was possible at 10 degrees C but not at 37 degrees C. Hence, all incubations of cells with Epo were carried out at 10 degrees C. Data on specific binding analyzed by the method of Scatchard demonstrated that yolk sac erythroid cells possess a single class of Epo receptors at each stage of gestation examined. Binding affinity and numbers of receptors per cell change as ontogeny progresses: Kd (the dissociation constant) increases, a phenomenon observed in other differentiating cell systems, whereas the number of receptors per cell peaks on gestational day 10. The variability in number of receptors per cell is consonant with up and down regulation controlled by Epo availability. We propose that the progressive increase in Kd might be best explained by ontogenic changes in cell membrane structure contiguous to the receptors themselves.

Animals↗
PubMed1975

The cytotoxins of cobra venoms. Isolation and partial characterization.

Eight basic proteins which lyse virus-transformed mouse fibroblasts in culture have been isolated from the venoms of six Asian Naja naja subspecies. These cytotoxins appear to represent an homologous series of proteins, all within the molecular weight range of 7000-8000. They have been divided into three arbitrary types on the basis of amino acid composition, electrophoretic mobilities and elution order upon ion-exchange chromatography. The rate at which the toxins effect cell lysis: (1) appears to be a function of the basicity of each toxin; (2) is dependent upon toxin concentration; (3) is temperature dependent; and (4) is inhibited by heparin sulfate. In view of the physical changes, which the cell undergoes during lysis and of the various factors which affect the action of these proteins, it is proposed that interaction of membrane receptors with the toxin, leading to alteration of cell membrane structure, is the principal event which ultimately leads to the disruption of the cell.

Amino Acids↗
PubMed1978

Biological activity of some oxygenated sterols.

A group of oxygenated sterols has been identified as potent and specific inhibitors of sterol biosynthesis. The ability of these compounds to inhibit sterol synthesis in cultured cells and the ineffectiveness of cholesterol under the same conditions suggest that feedback regulation of sterol biosynthesis may be brought about by an oxygenated sterol rather than by cholesterol. The nature of the regulatory sterol may vary in different cells with their specific requirements for cholesterol as a structural component or as a precursor of other steroid products. The use of oxygenated sterols to block sterol synthesis in cultured cells provides new information regarding the role of sterol in cell membrane structure and function. For example, de novo sterol synthesis is required for DNA synthesis and cell division by some cultured cells. Studies with cultured cells, and with rats and mice in vivo, suggest that oxygenated sterols could be of value in the treatment of several important human diseases.

Animals↗
PubMed1995

Binding of the fibrillar CS3 adhesin of enterotoxigenic Escherichia coli to rabbit intestinal glycoproteins is competitively prevented by GalNAc beta 1-4Gal-containing glycoconjugates.

We have attempted to characterize the binding specificity of the coli surface 3 (CS3) subcomponent of colonization factor antigen II of enterotoxigenic Escherichia coli, by means of an immunoblot method in which the binding of fimbriated bacteria to sodium dodecyl sulfate-polyacrylamide gel electrophoresis-separated rabbit intestinal cell membranes was evaluated. Isolated CS3 fibrillae as well as bacteria expressing CS3 on their surface bound to several intestinal cell membrane structures, i.e., structures present in the electrophoretic front and in the 30- to 35-kDa range and, most prominently, 120- to 140-kDa structures. Delipidization and protein digestion of the rabbit brush borders revealed that CS3 bound to structures of a proteinaceous nature. Sodium meta-periodate oxidation of the intestinal cell membranes abolished all their CS3 binding activity, indicating that CS3 bound to carbohydrate moieties of glycoproteins. The binding of CS3 to the separated intestinal proteins could also be inhibited by preincubation with the lectin derived from Maackia amurensis, indicating that CS3 bound to galactoproteins in the rabbit intestine. Inhibition experiments using equimolar amounts of various gangliosides demonstrated that GM1, asialo-GM1, and GM2 inhibited the binding of CS3 equally well, whereas GM3 was not as effective. These results suggested that the critical CS3 binding epitope consisted of the carbohydrate sequence GalNAc beta 1-4Gal. This was supported by electron microscopic experiments showing that this disaccharide, O linked to bovine serum albumin via a spacer, localized around CS3-positive bacteria but not at all around corresponding CS3-negative mutants. Furthermore, CS3-expressing bacteria recognized this neoglycoprotein when it was immobilized on nitrocellulose. The GalNAc beta 1-4Gal disaccharide has also been implicated as a binding structure for other pathogenic bacteria such as enteropathogenic E. coli and Pseudomonas aeruginosa.

Animals↗
PubMed1979

Morphological alteration of the stria vascularis after administration of the diuretic bumetanide.

Chinchillas were given either a single injection of the diuretic bumetanide (18 mg/kg body weight) or saline-sodium hydroxide and sacrificed at 10 min, 1 hr and 24 hr after the injection. Slight stria edema was present at 10 min, marked edema at 1 hr and no edema 24 h after bumetanide. The edema began in the first cochlear turn at 10 min and spread to the second turn by 1 hr. Along with edema, marginal cell bulging, potential capillary constriction and the formation of marginal cell membranous structures occurred after bumetanide treatment.

Animals↗
PubMed1987

The type of dietary fat affects the severity of autoimmune disease in NZB/NZW mice.

The type of dietary fat dramatically affects the onset of autoimmune disease in lupus-prone female New Zealand Black/New Zealand White F1 (B/W) mice. Disease development was strikingly slowed in mice fed a diet containing quantities of omega-3 fatty acids (fish oil, FO). By 10 months of age, 94% of the FO mice were still living, whereas all the mice fed a saturated fat diet (lard,L) were dead. Those mice fed a corn oil (CO) diet were intermediate with 35% alive at the 10-month time evaluation. Long after the L and CO groups had succumbed to glomerulonephritis, the FO group had negligible proteinuria. Both B and T cell function, particularly antibody production and resultant circulating immune complex (CIC) levels, were modified by the type of dietary fat. FO mice exhibited lower levels of anti-ds-DNA and lower levels of CICs than L or CO mice. B/W antibody response to a T-independent antigen (DNP-dextran) was enhanced at 8 months of age in FO mice, whereas it was suppressed in L mice. T-dependent (sheep red blood cell) responses at that time period were reduced in all the diet groups, a reflection of the reduced numbers of accessory T cells as determined by FACS analysis. The natural killer (NK) response to YAC-1 cells decreased in the L group from 5 to 9 months of age but remained unchanged in the CO and FO groups. Severe glomerulonephritis was the most common histopathologic finding in the L and CO groups. Arteritis was found in the spleens of nearly all the L and CO mice. Arteritis of the heart, colon and intestine, stomach, kidney, and liver were also seen principally in the L mice. In contrast, most FO mice had minimal to mild glomerulonephritis and no or minimal arteritis in the spleen. It is likely omega-3 fatty acids of fish oil reduce immune-complex-induced glomerulonephritis through production of prostaglandin metabolites with attenuated activity and/or through altering cell membrane structure and fluidity, which may, in turn, affect the responsiveness of immune cells.

Animals↗
PubMed1996

[Changes in the mitotic cycle of Chinese hamster CHLV-79 RJK cells resistant to ethidium bromide after the action of ionizing radiation].

A study was made of the effect of ionizing radiation on mitotic cycle and survival of the Chinese hamster cells of two clones-CHLV-79 RJK, and its derivative Vebr-30, resistant to ethidium bromide. Ethidium bromide resistant cells were more resistant to 1) lethal effects of gamma rays (by cell survival); 2) X-rays (by cell cycle recovery after irradiation of cells in a dose of 5 Gr); 3) colcemide treatment (by accumulation of cells in G2+M phase). These data may result from damaging a certain regulatory process, which may be involved in cell response to radiation damage and in repair of predominantly sublethal and partly lethal DNA lesions as well as of cell membrane structures.

Animals↗
PubMedDate not supplied

[Heterogeneity of protein metabolism and activities of certain enzymes in functionally different structures of nerve tissue].

The article deals with a review of the results of studies conducted at the department which evidence for inhomogeneity of localization, composition and different intensity of intravital renewal of proteins as well as for different activity of some enzymes most important for the nervous system functions in the macro- and microstructural formation of the nerve tissue. On the basis of the experimental data concerning the presence in the nerve tissue of a wide range of rates for intravital renewal of proteins in the structures of different functions as well as of those concerning subcellular and suborganoid localization of intracellular peptid-hydrolases, a conclusion is drawn that catabolism of the protein molecules occurs mainly on the cell membrane structures. The effect of acid peptide-hydrolases is chiefly manifested in the died and damaged cells and neutral ones in the intact functioning cells. As among the proteins most important functionally for the nervous activity ATP-hydrolyzing enzymes occupy a special place, the article provides basic data of studies in the ATPase activity in the nervous tissue, intracellular localization of the enzyme, its sensitivity to uni- and bivalent ions, as well as in the mechanism of interaction with ouabain--specific inhibitor and with melipramine--neurotropic substance.

Adenosine Triphosphatases↗
PubMed1982

Effects of amine substances on susceptibility of cells to agglutination by concanavalin A and on paracrystal formation by vinblastine in untransformed 3T3 cells.

The effects of a secondary amine (ketamine), tertiary amines (dibucaine, lidocaine, marcaine, propanidid, diazepam and chlorpromazine) and a quaternary amine (tetraethylammonium bromide, TEA) on mouse 3T3 cell agglutination by concanavalin A (Con A), on patch formation of Con A receptors on the cell surface, and on paracrystal formation by vinblastine in cytoplasm were studied. These amines enhanced the cell agglutination at low concentrations of Con A, as did the mixture of colchicine and cytochalasin B. Ca++, applied extracellularly, inhibited the effects of these amines on cell agglutination by Con A. The patch formation of Con A receptors on the cell surface as revealed by fluoresceinated Con A was enhanced by these amines. Ketamine, dibucaine and TEA inhibited the paracrystal formation in cytoplasm, as did Ca++ ionophores such as A-23187 and X-537-A. These results suggest that the amines tested affect the fluidity of Con A receptors by impairment of cell membrane structural proteins and result in the increase of the susceptibility of cells to agglutination by Con A.

Agglutination↗
PubMed1997

Intracellular calcium signalling in striated muscle cells.

Calcium signalling in cells is dependent on a communication between channels/ transporters in two membrane structures: the cell membrane and the membranes of endo- and sarcoplasmic reticula (ER/SR). In general, cytosolic Ca2+ can be raised by influx of calcium over the cell membrane through three types of channels: voltage-, receptor-, and store-operated channels (VOCs, ROCs and SOCs). This small Ca2+ influx is most often amplified by a Ca2+ release from the ER/SR through two types of channels: the IP3-receptor and the ryanodine receptor (RyR), which are huge proteins identified and cloned in recent years. We focus on the 'synaptic' connection between VOCs (L-type calcium channels) and RyRs of the SR in heart and skeletal muscle. Depolarization of the cell membrane (an action potential) opens the VOC and moves it in the membrane. One VOC triggers opening of a certain number of underlying RyRs that together release a quantum of calcium from the SR, a calcium spark. The communication between the VOC and RyRs is probably achieved primarily by a mechanical link in skeletal muscle (voltage-controlled calcium release), and by the small inward calcium flux through the VOC in the heart (calcium-induced calcium release, CICR). Conditions as different as heart failure, myasthenia gravis, malignant hyperthermia, and skeletal muscle fatigue, may be examples of deteriorated control or function of the RyR.

Calcium↗
PubMed1984

Hormone-induced cell death. 2. Surface changes in thymocytes undergoing apoptosis.

In vivo, apoptotic cells are swiftly recognized by phagocytes, presumably because of changes on their surface. This article describes surface changes in rat cortical thymocytes undergoing apoptosis induced by glucocorticoid treatment in vitro. Homogeneous populations of thymocytes early in apoptosis were prepared by isopyknic centrifugation. These cells were compared with purified nonapoptotic cells in terms of several surface characteristics, including binding to macrophages, surface ultrastructure, microelectrophoretic mobility (a measure of surface charge density), and ability to bind four lectins and four monoclonal antibodies to thymocyte antigens. Apoptotic cells bound to macrophages more avidly than did nonapoptotic cells by a process not dependent upon serum factors. Their surfaces lost microvilli and became " blistered ," apparently through fusion of vesicles of endoplasmic reticulum with the plasma membrane. The surface charge density of apoptotic cells was less than that of nonapoptotic cells. Surface antigens and lectin-binding sites were less abundant on apoptotic than on normal cells, in proportion to the general reduction in cell size observed in apoptosis. Differences between apoptotic and normal cells were not detected, however, in the relative quantities of exposed galactose, N-acetyl galactosamine, N-acetyl glucosamine, N-acetyl neuraminic acid, or of several surface antigens, including the major sialoglycoproteins of the thymocyte membrane. It appears that although several changes occur in the surface of apoptotic cells, many cell membrane structures remain intact. The changes responsible for the recognition of apoptotic cells by phagocytes are more subtle than those detectable by the binding of lectin and antibody probes, but preliminary data suggest that a lectin-sugar interaction is involved.

Animals↗
PubMed1994

Alteration of brain cell membrane function following cocaine exposure in the fetal guinea pig.

The effect of cocaine on brain cell membrane structure and function was studied in the fetal guinea pig. We tested the hypothesis that cocaine, a potent vasoconstrictor, would result in brain cell membrane dysfunction as determined by altered activity of Na+,K(+)-ATPase and the appearance of products of membrane lipid peroxidation (conjugated dienes (CD) and fluorescent compounds (FC)). A total of 14 pregnant guinea pigs were studied at term (60 days). One hour prior to delivery, the pregnant guinea pigs were divided into 3 groups as follows: cocaine, 30 mg/kg i.p., saline placebo i.p., or 7% FiO2 for 1 h. Following cocaine, brain Na+,K(+)-ATPase activity decreased (mean +/- S.D., 25.6 +/- 9.2 vs. 54.6 +/- 3.4 mumol Pi/mg protein/h, cocaine vs. control, respectively, P < 0.01) and was similar to the hypoxia group (21.9 +/- 2.8 mumol Pi/mg protein/h). The products of lipid peroxidation did not change significantly following cocaine whereas hypoxia resulted in a rise in CD from 0 to 0.175 +/- 0.015 mumol/g brain, control vs. hypoxia, (P < 0.01), and FC from 1.13 +/- 0.15 to 1.88 +/- 0.13 micrograms quinine sulfate/g brain, control vs. hypoxia, (P < 0.01). These data show that acute fetal cocaine exposure, unlike hypoxia alone, results in a significant decrease in Na+,(K+)-ATPase activity without a significant increase in the products of lipid peroxidation, suggesting the mechanism by which cocaine affects brain cell membrane integrity is distinct from hypoxia. Inhibition of the enzyme activity may be due to a direct action of cocaine on the enzyme or due to enzyme regulation by cocaine-induced alterations in neurotransmitters.

Animals↗
PubMedDate not supplied

Cryopreservation of mammalian sperm: what we ask them to survive.

Techniques for freezing bull sperm developed over the past 40 years have not yielded protocols for preserving sperm from other species. Recent advances in our understanding of cell membrane structure function and metabolism now permit alternative modes of investigation. These data will allow development of unique studies which should have a higher probability of yielding successful protocols for sperm from other species. In this review the authors will: (1) provide a general overview of cryopreservation; (2) review emerging concepts of membrane structure and the relationship of membrane composition to water and cryoprotectant movement; (3) emphasize how these parameters affect cell volume and surface areas; (4) focus attention on the concept that cryoprotectants will alter membrane structure and function in addition to their well-recognized effects on bulk solvent; and (5) emphasize the effect of the processing protocol on metabolic balance. These concepts are reintroduced in the context of the established and successful protocol for freezing bull sperm to illustrate the molecular responses that may be necessary to survive a freeze-thaw cycle.

Animals↗
PubMed1975

Changes in liver and gastric mucosal hexosamine synthesis after restraint.

The specific activity of L-glutamine: D-fructose-6-phosphate aminotransferase was measured in the oxyntic gland mucosa and liver of fasted, male rats after immobilization in a cold environment. Immobilization for 3 hr resulted in 100% frequency of lesion formation associated with decreased enzyme activity in oxyntic gland mucosa (70.1 plus or minus 5.9% of control) and liver 25.2 plus or minus 5.2% of control). Enzyme activity had returned to control level in the stomach 9 hr after immobilization, and in the liver 21 hr after immobilization. Immobilization for 1 1/2 hr decreased oxyntic gland mucosa enzyme activity to 21.0 plus or minus 9.8% of control, although the frequency of lesion formation was only 62.5%. Liver enzyme activity was 51.3 plus or minus 12.8% of control. Concentrations of UDP-N-acetylhexosamines, feedback inhibitors of this enzyme, were not altered in either tissue. Adrenalectomy, which increased the frequency of damage after 1 hr of immobilization, enhanced the decreases in enzyme activity in both tissues, while atropine sulfate, which decreased the frequency of damage after 3 hr of immobilization, had no significant effect on the enzyme. Thus, immobilization of rats in a cold environment decreases or alters the synthesis of hexosamine-containing compounds through a mechanism not dependent on acid secretion or adrenocorticoids. This alteration in synthesis may result not only in abnormal mucus secretion, but also in altered cell membrane structure and function.

Adrenal Cortex Hormones↗
PubMed1980

Effect of magnesium-dependent cell membrane alterations on the transport of K+ in Ehrlich ascites tumour cells.

Mg-deficiency or Mg-loading of tumour cells changes the permeability of the cell membrane. The influence of this change on the K+ transport across the membrane was investigated using 86Rb+ and K+ analog. The time course of the influx and efflux rates were estimated by means of a mathematical approach for a two-compartment system with inconstant pool sizes. The comparison of the two states of the cells demonstrates that in Mg-deficient cells the passive K+ efflux is significantly enhanced (40%). This in turn stimulates the active counter transport mediated by the (Na+-K+)-ATPase, raising the ATP consumption by about 30%. However, the enzyme is not able to maintain the cellular K+ content under these conditions. After a short transient increase due to the initially enhanced influx the passive net efflux prevails. Differences in the electrophoretic mobility of the two states of the cells confirm Mg-dependent changes of the cell membrane structure.

Animals↗
PubMed1984

The physico-chemical mechanism of mediated transport. I. Facilitated diffusion.

On the basis of the currently accepted model for the cell membrane structure, a physico-chemical model for mediated transport is developed and solved for the case of polar non-electrolyte migration through the cell membrane. The model considers the interstitial space defined by the transport protein subunits to be the migration pathway for polar solutes. A Langmuir-type adsorption equilibrium is assumed at the interfaces and a multicomponent diffusion mechanism of solute and water is postulated within the migration pathway, where the polar residues of the transport protein represent another component of the system. Membrane selectivity is governed by the adsorption constants, which are shown to affect strongly the kinetics of transport. Isosmotic transport and the volume change of the cell are important features incorporated in the model, which is shown to fulfill the peculiar properties of facilitated diffusion systems. It is concluded that the same type of pathway can be used for the transport of other polar solutes through existing or induced hydrophilic channels, for which a similar approach is suggested.

Adsorption↗