Effect of vinblastine sulfate, colchicine and lumicolchicine on membrane organization of normal and transformed cells

A role for the cytoskeleton in heat-shock-mediated thermoprotection of locust neuromuscular junctions

A prior hyperthermic stress (heat shock) can induce thermoprotection of neuromuscular transmission in Locusta migratoria extensor tibiae muscle measured 4 h after the onset of the heat shock. It is not clear what effect an acute hyperthermic stress may have on the nervous system's ability to tolerate thermal stress, that is, before increased expression of heat-shock proteins. We found that over consecutive thermal stress tests, failure temperature was not altered in either heat-shock or control animals. This suggests that protective mechanisms are not established in the short term (within one hour). Various members of the heat-shock protein family interact with elements of the cytoskeleton. We found that preexposure of the preparation to cytoskeletal stabilizing drugs induced thermoprotection, while preexposure to cytoskeletal disrupting drugs disrupted the ability to confer and maintain thermoprotection. We conclude that thermoprotection relies on a stable cytoskeleton and suggest that members of the heat shock protein family are involved.

Astrocytes: a possible primary site for colchicine-mediated neurotoxicity in the rat striatum

Ultrastructural changes in rat astrocytes including endfoot swelling and rupture of plasma membranes were seen as early as 1 h after injection of 6.0 micrograms colchicine (CO) into the striatum. Significant change in neuronal morphology was not seen by 24 h. Astrocytes may therefore be primary targets for CO-mediated damage, which then may have secondary neurotoxic consequences.

Influence of antimicrotubular drugs on the Golgi apparatus of stomach secretory mucoid cells and small intestine absorptive cells

The effects of vinblastine and colchicine on the Golgi apparatus of stomach surface mucoid and absorptive intestinal cells were compared by cytochemical analysis. The two epithelial cells were chosen because of their different specific functions in the formation of secretory granules, the production of lysosomes and the intensity of membrane traffic in the cytoplasm. For the analysis, adult mice were injected with 1 mg/100 g b.w. of vinblastine and 1 mg/100 g b.w. of colchicine. For the demonstration of cis and trans cisternae of the Golgi apparatus, prolonged osmification, thiamine pyrophosphatase and acid phosphatase activity identification were applied. After treatment with vinblastine or colchicine, polarity of stacks in the Golgi apparatus of surface mucoid cells is preserved although the number of cisternae with thiamine pyrophosphatase or acid phosphatase activity decreases. However, the Golgi apparatus of intestinal absorptive cells completely disintegrates and only a few separated cis or trans cisternae can be identified. The main effect seems to be a reduction of vesicles which can be cytochemically identified as parts of the Golgi apparatus and an accumulation of vesicles which probably originate from budding ER. Communication between the ER and the Golgi apparatus seems to be interrupted.

Neuronal damage in the albino rat: excitotoxin, microtubule inhibitor synergism

Separate lines of investigation implicate excitotoxins or disruption of cytoskeletal architecture in the pathogenesis of human neurodegenerative disease. To assess the hypothesis that these neurotoxic mechanisms may have a synergistic effect, albino rats were given intrastriatal administrations of either the excitotoxin, kainic acid, or the microtubule inhibitor, colchicine, or both. Assessment of neuronal damage, either by loss of neurotransmitter metabolic enzyme activities or by histologic analysis, demonstrated synergism between the agents. Further, the synergism was still apparent with substitution of quinolinic acid, but not dimethyl kainate, for kainic acid, and Vinca alkaloids, but not lumicolchicine, for colchicine.

The role of spindle microtubules in the timing of the cell cycle in echinoderm eggs

Spindle microtubules play an important role in the mechanisms that control the timing of cell cycle events in the eggs of the sea urchins L. variegatus and L. pictus. However, recent work which used colchicine to block microtubule assembly in the eggs of two other echinoderms, S. purpuratus and D. excentricus, has raised serious questions about the generality of this role for spindle microtubules. Thus, we have systematically examined the role of spindle microtubules in the timing of the cell cycle in the fertilized eggs of these latter species. We treated eggs of both species with 5-10 microM Colcemid for several minutes starting 30 min after fertilization to completely prevent spindle microtubule assembly for several h. We used Colcemid, instead of colchicine, because it is effective at lower doses and, at these doses, shows no detectable toxic side effects. We compared for control and treated eggs the time course of nuclear envelope breakdown/reformation and DNA synthesis. We found for both species that the eggs continue to cycle without spindle microtubules; mitosis is up to twice the normal duration while interphase remains essentially unaffected. To test for the possible toxic side effects of the 1-2 mM colchicine used earlier on S. purpuratus and D. excentricus, we treated eggs of these two species, and also those of L. variegatus, with 1 mM lumi-colchicine. This photo-inactivated form of colchicine, which does not bind to tubulin, substantially prolongs mitosis and, to a lesser extent, interphase. Thus, the results of the earlier work are most easily explained by the combination of specific and nonspecific effects of the 1-2 mM colchicine used. Our present results indicate that the importance of spindle microtubules in the mechanisms that control the timing of the mitosis portion of the cell cycle is a general phenomenon.

Influence of colchicine and vinblastine on the intracellular migration of secretory and membrane glycoproteins: III. Inhibition of intracellular migration of membrane glycoproteins in rat intestinal columnar cells and hepatocytes as visualized by light and electron-microscope radioautography after 3H-fucose injection

In the first paper of this series (Bennett et al., 1984), light-microscope radioautographic studies showed that colchicine or vinblastine inhibited intracellular migration of glycoproteins out of the Golgi region in a variety of cell types. In the present work, the effects of these drugs on migration of membrane glycoproteins have been examined at the ultrastructural level in duodenal villous columnar cells and hepatocytes. Young (40 gm) rats were given a single intravenous injection of colchicine (4.0 mg) or vinblastine (2.0 mg). At 10 min after colchicine and 30 min after vinblastine administration, the rats were injected with 3H-fucose. Control rats received 3H-fucose only. All rats were sacrificed 90 min after 3H-fucose injection and their tissues processed for radioautography. In duodenal villous columnar cells, 3H-fucose labeling of the apical plasma membrane was reduced by 51% after colchicine and by 67% after vinblastine treatment; but there was little change in labeling of the lateral plasma membrane. Labeling of the Golgi apparatus increased. This suggests that labeled glycoproteins destined for the apical plasma membrane were inhibited from leaving the Golgi region, while migration to the lateral plasma membrane was not impaired. In hepatocytes, labeling of the sinusoidal plasma membrane was reduced by 83% after colchicine and by 85% after vinblastine treatment. Labeling of the lateral plasma membrane also decreased, although not so dramatically. Labeling of the Golgi apparatus and neighboring secretory vesicles increased. This indicates that the drugs inhibited migration of membrane glycoproteins from the Golgi region to the various portions of the plasma membrane. Accumulation of secretory vesicles at the sinusoidal front suggests that exocytosis may also have been partially inhibited. In both cell types, microtubules almost completely disappeared after drug treatment. Microtubules may, therefore, be necessary for intracellular transport of membrane glycoproteins, although the possibility of a direct action of these drugs on Golgi or plasma membranes must also be considered.

Antagonism by taxol of effects of microtubule-disrupting agents on lymphocyte cAMP metabolism and cell function

Several microtubule-disrupting agents (colchicine, demecolcine, vinblastine, vincristine, podophyllotoxin, and nocodazole) have been shown to inhibit lymphocyte-mediated cytolysis. These agents also enhanced the prostaglandin E1-induced rise in cAMP levels in these cytolytic lymphocytes. Taxol, a natural product alkaloid that has been shown to enhance microtubule polymerization and to stabilize microtubules, antagonized both of these effects of the microtubule-disrupting agents in the cytolytic lymphocytes. Taxol also antagonized the enhancement of cAMP increases by colchicine in lymphocytes stimulated by 2-chloroadenosine, isoproterenol, and cholera toxin. The enhancement of the prostaglandin E1-induced cAMP response caused by treatment of the lymphocytes with either cytochalasin B or 3-deazaadenosine in the presence or absence of L-homocysteine was not antagonized by taxol. Taxol, colchicine, or the combination of these two agents did not affect ATP levels in cytolytic lymphocytes. These results support a modulatory role for microtubules in both the cytolytic process and the production of cAMP in these lymphocytes.

Colchicine in refractory chronic lymphocytic leukemia. A Southwest Oncology Group study

Fourteen patients with active chronic lymphocytic leukemia who had failed prior therapy were treated with progressive doses of weekly intravenous colchicine beginning at 2 mg and escalating as high as 7 mg in a single injection. Responses were seen in two of 14, with a lessening of adenopathy and splenomegaly. Toxicity was characterized by gastrointestinal intolerance in eight and thrombocytopenia in 12. There is activity of the drug in chronic lymphocytic leukemia but, as administered in this study, high dose therapy is not ideal and it may be more beneficial if the drug were given as low dose daily or weekly therapy.

The effects of microtubule dissociating agents on the physiology and cytology of the sensory neuron in the femoral tactile spine of the cockroach, periplaneta americana L

Microtubules are prominent cellular components of the mechanosensory and chemosensory sensilla associated with the insect cuticle, and a range of hypotheses have been proposed to account for their role in sensory transduction. Chemical agents such as colchicine and vinblastine, which dissociate microtubules, also interfere with transduction in these sensilla, and this has been attributed to their anti-microtubule activity. We have now examined the dynamic properties of sensory transduction in the mechanosensitive neuron of the cockroach femoral tactile spine, after the application of colchicine, vinblastine and lumicolchicine. Concurrently we have examined the ultrastructure of the same sensory ending by transmission electron microscopy. All of the drugs reduced the mechanical sensitivity o the receptor. Colchicine and vinblastine achieved this reduction without altering the dynamic properties of the receptor but lumicolchicine changed the dynamic response, and increased the relative sensitivity to rapid movements. Conduction velocity, another measure of neuronal function, which relies upon ionic currents flowing through the membrane, was reduced by all three drugs. The effects of the drugs upon the ultrastructure of the sensory ending were also disparate. In the case of colchicine there was complete dissociation of microtubules in the tubular body and distal dendrite before a total loss of mechanical sensitivity. Vinblastine was less effective in dissociating microtubules, although more effective in the reduction of mechanical sensitivity. With lumicolchicine the dominant morphological effect was a severe disruption of the dendritic membrane. We conclude from these experiments that microtubules are not essential in the transduction of mechanical stimuli by cuticular receptors and that the effects of these drugs upon mechanosensitivity are not directly related to their dissociation of the microtubules in the tubular body, but are more likely to arise from actions upon the cell membrane. These actions could include effects upon tubulin in the membrane or upon other membrane components.

Colchicine alters the nerve birefringence response

The internal perfusion of squid axons with colchicine reversibly and selectively reduces the transient sodium current and the birefringence response to a brief depolarizing voltage pulse.

Effect of mitotic inhibitors on the ultrastructure of root meristem cells

After 5 h in 10(-3)M vinblastine the most obvious effects upon Vicia faba L. cells are seen in the spindle apparatus. These include the microtubules themselves as indicated by c-type metaphases and the pole regions of otherwise intact spindles, leading to multipolar anaphases and to telophases with more than two daughter nuclei. Vesicle transport may be undisturbed and new cell walls can be formed, although cases of disturbed cell plate and cell wall formation were noted occasionally, accompanied by myelinizations in phragmosomes. After 24 h in the same concentration of vinblastine, divisions are no longer observed and the plasma membranes are severely affected. They show extensive myelinizations, accumulations of lipids and dehiscence from the cell walls which are frequently thickened and irregularly formed. Of the other cellular membranes, the nuclear envelope and, more frequently, the tonoplast may be affected. Electron-dense deposits appear in the vacuoles. Comparable, though less severe, changes including multipolar anaphases and myelinizations result from treatment with lumicolchicine, but not with colchicine. Vinblastine leads to the appearance of filament bundles both in cytoplasm and karyoplasm, lumicolchicine to morphologically identical filaments in the cytoplasm alone. The nature of these filaments is unknown.

High voltage electron microscopy studies of axoplasmic transport in neurons: a possible regulatory role for divalent cations

Light and high voltage electron microscopy (HVEM) procedures have been employed to examine the processes regulating saltatory motion in neurons. Light microscope studies demonstrate that organelle transport occurs by rapid bidirectional saltations along linear pathways in cultured neuroblastoma cells. HVEM stereo images of axons reveal that microtubules (Mts) and organelles are suspended in a continuous latticework of fine microtrabecular filaments and that the Mts and lattice constitute a basic cytoskeletal structure mediating the motion of particles along axons. We propose that particle transport depends on dynamic properties of nonstatic microtrabecular lattice components. EXperiments were initiated to determine the effects of changes in divalent cation concentrations (Ca2+ and Mg2+) on: (a)the continuation of transport and (b) the corresponding structural properties of the microtrabecular lattice. We discovered that transport continues or is stimulated to a limited extent in cells exposed to small amounts of exogenously supplied Ca2+ and Mg2+ ions (less than 0.1 mM). Exposure of neurons to increased dosages of Ca2+ and Mg2+ (0.2-1.0 mM) stimulates transport for 2-4 min at 37 degrees C, but after a 5- to 20-min exposure the saltatory movements of organelles are observed gradually to become shorter in duration and rate particle motion ceases to occur. HVEM observations demonstrated that Ca2+ - and with the cessation of motion. Ca2+-containing solutions produced contractions of the microtrabecular filaments, whereas Mg2+-containing solutions had the opposing effect of stimulating an elongation and assembly (expansion) of microtrabeculae. On the basis of these observations we hypothesize that cycles of Ca2+/Mg2+-coupled contractions and expansions of the microtrabecular lattice probably regulate organelle motion in nerve cells.

Colchicine reversibly inhibits electrical activity in arthropod mechanoreceptors

Colchicine and some other microtubule-active agents inhibit the electrical responses of cockroach tibial spine mechanoreceptors. Lumicolchicine, a colchicine analog which does not bind to microtubule protein, does not inhibit mechanoreceptive responses. Colchicine inhibition of peripheral mechanoreceptive responses is fully reversible and dose dependent, but colchicine has no effect on conduction in leg nerve axons. Colchicine inhibition is therefore an effect on the sensory dendrites or soma. The inhibition produced by colchicine could be produced by several effects. Colchicine may inhibit because it (1) disrupts the numerous intracellular microtubules which are a part of this sensory receptor's dendrite, (2) blocks axoplasmic transport of essential materials to the sensory dendrite, or (3) binds to tubulin or other proteins in the dendritic membrane.

Autophagocytosis in mouse seminal vesicle cells in vitro. Temperature dependence and effects of vinblastine and inhibitors of protein synthesis

Spontaneous autophagocytosis was observed in mouse seminal vesicle cells during incubation for 2 h in vitro. The number of autophagic vacuoles formed was greatest at 37 degrees C and decreased when the temperature was lowered. At 22 degrees C it reached the near-zero value characteristic of non-incubated control cells. Incubation of the cells at 37 degrees C in the presence of 0.1 mg/ml vinblastine sulfate resulted in a marked increase in the number of autophagic vacuoles, but the drug was ineffective at 22 degrees C. Puromycin (10(-3) M) exerted no influence on spontaneous autophagocytosis, but cycloheximide in concentrations from 10(-7) M to 10(-3) M inhibited both spontaneous and vinblastine-induced autophagocytosis. The formation of tubulin paracrystals in vinblastine treated cells was not prevented either by low (22 degrees C) temperature or in the presence of cycloheximide.

Fast axonal transport in the presence of high Ca2+: evidence that microtubules are not required

Microtubules have long been associated with the mechanism of fast axoplasmic transport, although experimental evidence to support an involvement has been equivocal. Electron microscopic studies demonstrated that incubation of the axons of excised rat sciatic nerves in media containing 75 mM Ca2+ caused complete loss of microtubules within 6 hr. To evaluate the role of microtubules in fast anterograde transport, studies of transport in nerves exposed to these conditions were undertaken. Prior to measurement of axoplasmic transport, nerves ligated distal to the dorsal root ganglia were preincubated in vitro in 75 mM Ca2+ for 0-6 hr. Fast axonal transport was subsequently monitored by measuring the amount of trichloroacetic acid-insoluble radioactivity that accumulated at the ligature after incubation for 12-18 hr with L-[3H]proline. Nerves in which microtubules had been depolymerized by preincubation in high Ca2+ maintained control levels of transport. We conclude that intact microtubules are not required for fast anterograde axoplasmic transport.

Correlative statistical analysis and computer modelling of intramembraneous particle distributions in human erythrocyte membranes

The planar distribution of intramembranous particles on the P faces of freeze-fractured human erythrocyte membranes is characterized by radial distribution, angular distribution and differential density distribution analysis. Various degrees of intramembranous particle aggregation induced by spectrin removal and low pH are differentiated through computation. Random hard disk models with various disk diameters are built for comparison studies. In all samples, the 80 +/- 10 A particles are found to have a preferred neighboring distance of 100 +/- 10 A, but no preferred angular relation is found between neighboring particles. A pattern recognition process using both radial and density distribution analyses reveals that none of the particle distributions observed may be regarded as random. The fact that the particle distributions observed are neither even nor random suggests that factors other than long range electrostatic force alone are involved in determining the particle distribution.

The effects of vinblastine on acinar cells of the exorbital lacrimal gland of the rat

The effects of vinblastine treatment on acinar cells of the rat exorbital lacrimal gland were studied by electron microscopy. Experimental animals of both sexes were given single intraperitoneal injections of (1) vinblastine (4 mg/kg body weight) at 1 to 24 h before sacrifice; (2) pilocarpine (20 mg/kg b.w.) for 1 h; or (3) vinblastine for 1 h followed by pilocarpine for 1 h. Vinblastine treatment caused a number of changes including autophagocytosis, formation of intracisternal granules, and alteration of secretory granules. These changes varied in extent and onset between male and female rats. In addition, the Golgi apparatus was reduced in size and dispersed throughout the cytoplasm. Mitotic figures were commonly observed. Moreover, vinblastine inhibited the pilocarpine-stimulated degranulation of the acinar cells. In view of the known anti-microtubular action of vinblastine, these results suggest that microtubules are involved in various aspects of the transport, packaging, and secretion of exportable proteins in the lacrimal gland. Additionally, autophagocytosis and alteration of secretory granules may partially result from the interaction of vinblastine with membranes.

F20C, a new fluorescent membrane probe, moves more slowly in malignant and mitogen-transformed cell membranes than in normal cell membranes

New fluorescent probes of membrane mobility can be introduced into cell membranes at single points with particles of a membrane mobility agent, A2C. The initial entry of fluorescence from the particle into the cell membrane and the subsequent lateral spread of fluorescence have been observed for cells in suspension. A dramatic difference between the behavior of normal lymphocytes and that of mitogen-transformed and mastocytoma cells is found. Both the initial entry and the spreading of fluorescence are much slower in the transformed and tumor cells than in the normal cells at 18 degrees C. Entry and spread of fluorescence in normal cells become slow enough to be observed only at 12 degrees C or below.

Freeze-fracture of monolayer cultures

This paper describes a simple method for the freeze-fracturing of cells in monolayers or multi-layer tissue cultures. The method produces high quality replicas and is applicable to the study of virtually any tissue culture or organ culture system. It uses standard materials and equipment for both tissue culture and freeze-fracturing.

Motility of Mycoplasma pneumoniae

Cell of Mycoplasma pneumoniae FH gliding on a glass surface in liquid medium were examined by microscopic observation and quantitatively by microcinematography (30 frames per min). Comparisons were made only within the individual experiments. The cells moved in an irregular pattern with numerous narrow bends and circles. They never changed their leading end. The average speed (without pauses) was relatively constant between o.2 and 0.5 mum/s. The maximum speed was about 1.5 to 2.0 mum/s. The movements were interrupted by resting periods of different lengths and frequency. Temperature, viscosity, pH, and the presence of yeast extract in the medium influenced the motility significantly; changes in glucose, calcium ions, and serum content were less effective. The movements were affected by iodoacetate, p-mercuribenzoate, and mitomycin C at inhibitory or subinhibitory concentrations. Sodium fluoride, sodium cyanide, dinitrophenol, chloramphenicol, puromycin, cholchicin, and cytochalasin B at minimal inhibitory concentrations did not affect motility. The movements were effectively inhibited by anti-M. pneumoniae antiserum. Studies with absorbed antiserum suggested that the surface components involved in motility are heat labile. The gliding of M. pneumoniae cells required an intact energy metabolism and the proteins involved seemed to have a low turnover.

Cell surface changes accompanying myoblast differentiation

Myoblasts are mononucleated cells and associated with differentiation undergo cell fusion and become multinucleated. The current studies have examined cell surface dynamic changes of Concanavalin A lectin receptor mobility and the role of hormones in modulating myoblast differentiation. A uniform distribution of Con-A receptors is observed in undifferentiated cells when reacted with Con-A at 37 degrees C. Cells from differentiating cultures or fully differentiated myotubes reacted similarly at 37 degrees C show a significant redistribution of Con-A into patches, "caps," and endocytic vesicles containing Con-A. If undifferentiated and differentiated cells are first prefixed with glutaraldehyde then reacted with Con-A continuous distribution of Con-A is seen across the cell surface. This suggests redistribution of Con-A and its receptors occurs in differentiated cells reacted with lectin at 37 degrees C. It is further shown that insulin (10 microgram/ml) significantly enhances myoblast differentiation but that this occurs after an apparent stimulation of proliferation. In contrast to insulin, dexamethasone (10 micron and 100 micron) profoundly inhibits myoblast differentiation while having different effects on proliferation; 10 micron dex stimulates cell growth while 100 micron dex suppresses cell proliferation. Lastly, an extracellular filamentous matrix which binds Con-A is observed at the ultrastructural level in high density cultures. No significant redistribution of Con-A is observed on this matrix in distinction to the redistribution observed on the cell membrane in differentiated cells.

Effects of local anaesthetics on intracellular fusion processes. Enhancement of concanavalin A-induced macrophage vacuolation

The extensive vacuolation elecited in mouse peritoneal macrophages in response to interaction with concanavalin A is markedly enhanced by a simultaneous exposure to anaesthetics. The potency of enchancing vacuolation increases within the series of normal alcohols with chain length C10 greater than C8 greater than C7 greater than C6. From the four tertiary amine local anaesthetics tested lidocaine and procaine are by far more effective than tetracaine and dibucaine. The latter two induce extensive cell shrinkage at concentrations at which the first two exhibit optimum enhancing capacity. Of the tested compounds chlorpromazine has the highest membrane/buffer partition coefficient and it exhibits its optimum enhancing effect on concanavalin A-induced macrophage vacuolation at the lowest drug concentration. The binding of [3H] concanavalin A as well as its internalization by macrophages incubated with the lectin for 15, 45 and 90 min are not affected significantly in the presence of decanol, procaine or chlorpromazine at concentrations of maximum enhancing effect on vacuolation. Thus enhancement of vacuolation does not stem from an increase in the rate or extent of concanavalin A interiorization. The rate at which vacuoles are generated is however markedly increased in the presence of chlorpromazine and the resulting vacuoles are of a larger diameter. At 2-5 fold the concentration required for inhibition of maximum enhancing effect, the drugs lead to extensive macrophage shrinkage and to depletion of intracellular ATP. Phagocytosis of heat-killed yeast cells is reduced by tertiary amine anaesthetics at concentrations optimal for enhancement of concanavalin A-induced vacuolation. Enhanced intracellular fusion of concanavalin A-bearing pinosomes to form vacuoles is discussed in terms of current ideas on factors vacuoles is discussed in terms of current ideas on factors vacuoles is discussed in terms of current ideas on factors affecting membrane fusion and the effects of anaesthetics on membrane organization of lipids, intramembraneous particles, glycoprotein receptors and the possible control by cytoskeletal elements. The results best fit the hypothesis that enhanced fusion correlates with membrane aggregation of both intramembraneous particles and concanavalin A receptor and the formation of areas relatively deplete of these structures and enriched in phospholipids.

Association of microfilament bundles with lysosomes in polymorphonuclear leukocytes

The juxtaposition of microfilament bundles and lysosomes seen both in thin-sectioned cells in the transmission electron microscope and in cryofractured cells in the scanning electron microscope, and the presence of short filamentous structures between lysosomes and microfilament bundles, suggest that microfilaments may be attached to lysosomal membranes and that these filaments may be involved in lysosomal movements. Further work is in progress to test these hypotheses.

Membrane anomalies of neoplastic cells

Neoplastic cells exhibit numerous membrane anomalies. Those involving the plasma membrane have attracted the greatest attention, although ample evidence indicates that the membranes of mitochondria, endoplasmic reticulum and lysosomes are also profoundly implicated. The information on these topics is briefly reviewed and it is concluded that of the multiple membrane anomalies observed, those responsible for high aerobic lactate production, abnormal plasma membrane transport and release of hydrolytic enzymes may figure prominently in malignant behaviour, i.e. invasiveness and metastasis. It is proposed that the membrane polymorphism of neoplastic cells can be explained in terms of the Changeux membrane lattice hypothesis. In particular it is suggested that the concerted behaviour of tumor cell membranes might deviate from normal due to one or more of the following processes: (a) insertion of a new protein (or lipid); (b) alteration of existing proteins (or lipids); (c) change in the proportion of phospholipid; (d) change in the proportion of glycolipid; (e) change in the proportion of cholesterol; (f) change in the steady-state of membrane ligands. The validity of this proposal is evaluated in terms of recent advances in membrane molecular biology.

Membrane pathology of normal and malignant cells--a review

The plasma membrane has been shown to play a critical role in the regulation of cell growth and proliferation, and pathologic change in the plasma membrane has been detected in neoplastic cells. This article reviews the structure and functions of biological membranes and discusses the differences that have been reported in the plasma membranes of normal and malignant cells that may be associated with neoplastic transformation.