Direct evidence for a colchicine-induced impairment in the mobility of membrane components

Plasma membrane tubulin

The association of tubulin with the plasma membrane comprises multiple levels of penetration into the bilayer: from integral membrane protein, to attachment via palmitoylation, to surface binding, and to microtubules attached by linker proteins to proteins in the membrane. Here we discuss the soundness and weaknesses of the chemical and biochemical evidence marshaled to support these associations, as well as the mechanisms by which tubulin or microtubules may regulate functions at the plasma membrane.

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.

Highly cohesive monolayers of lipid derivatives of colchicine: a dynamics study

Monolayers of lipid derivatives of colchicine spread at the air--water interface reach the thermodynamic equilibrium over an abnormally long period of time. Dynamics of this equilibration and the behavior of the film during compression--decompression cycles are observed by fluorescence microscopy. The thermodynamically disfavored structures observed are unrelated to previously described unusual shapes in the liquid expanded-gas coexistence regions. The relation between the cholesterol-like effect of the colchicinoid moiety, its propensity to dimerize, and the high viscosity of the monolayer are discussed.

The interaction between lipid derivatives of colchicine and tubulin: consequences of the interaction of the alkaloid with lipid membranes

Colchicine is a potent antimitotic poison which is well known to prevent microtubule assembly by binding tubulin very tightly. Colchicine also possesses anti-inflammatory properties which are not well understood yet. Here we show that colchicine tightly interacts with lipid layers. The physical and biological properties of three different lipid derivatives of colchicine are investigated parallel to those of membrane lipids in the presence of colchicine. Upon insertion in the fatty alkyl chains, colchicine rigidifies the lipid monolayers in a fluid phase and fluidifies rigid monolayers. Similarly X-ray diffraction data show that lecithin-water phases are destabilized by colchicine. In addition, an unexpectedly drastic enhancement of the photoisomerization rate of colchicine into lumicolchicine in the lipid environment is observed and further supports insertion of the alkaloid in membranes. Finally the interaction of colchicine with lipids makes the drug inaccessible to tubulin. The possible in vivo significance of these results is discussed.

Reduction of human recombinant type II phospholipase A2 and prostaglandin F2 alpha release by microtubule depolymerizing agents

1. The present study examines the effects of the microtubule depolarizing agent colchicine on secretory type II phospholipase A2 (PLA2) function in Chinese hamster ovary (CHO) cells that specifically overexpress human type II PLA2 and the effect of both colchicine and tubulazole on the release of type II PLA2 and prostaglandin (PG) F2 alpha from human placental explants. 2. Significant suppression by colchicine (0.01-10 mumol/L) of PLA2 activity (P < 0.00001), immunoreactive type II PLA2 (irPLA2; P < 0.00001) and PGF 2 alpha release (P < 0.01) was observed in medium from overexpressing CHO cells. These effects were significantly reduced (P < 0.0001) in the presence of 10 mumol/L taxol, an agent that prevents depolymerization of microtubules. The addition of 30 mumol/L arachidonic acid significantly reduced (P < 0.0001) the inhibition of PGF2 alpha production in CHO cell lines. 3. The addition of 1 mumol/L colchicine to human placental explants for 24 h significantly reduced irPLA2 (P < 0.00001) and PGF2 alpha production (P < 0.00001). Similarly, 1 mumol/L tubulazole significantly blocked irPLA2 (P < 0.001) and PGF2 alpha (P < 0.0001). 4. At 10 mumol/L, taxol significantly reduced irPLA2 inhibition by colchicine (n = 8; P < 0.05) and tubulazole (n = 8; P < 0.05). Similarly, taxol significantly reduced the reduction in PGF2 alpha production caused by colchicine (P < 0.001) and by tubulazole (P < 0.001). 5. These results suggest that integrity of the microtubule system is required for PLA2 function and the subsequent production of pro-inflammatory mediators.

Colchicine in dermatology

Colchicine is a medication most often used to treat symptoms of gout. This drug has also been shown to have beneficial effects on cutaneous conditions, including leukocytoclastic vasculitis, psoriasis, and Sweet's syndrome. Colchicine inhibits the function of polymorphonuclear leukocytes, and dermatoses with a strong presence of these cells may benefit the most from the administration of this medication. A review of the pharmacology, mechanism of action, and adverse reactions of colchicine is also presented.

Is signal transduction modulated by an interaction between heterotrimeric G-proteins and tubulin?

Although it is generally accepted that tubulin plays an important role in G-protein-mediated signal transduction in a variety of systems, the mechanism of this phenomenon is not completely understood. G-protein-tubulin interaction at the cell membrane and the cytosol, and the influence of such an interaction on cellular signaling are discussed in this review article. Because the diameter of a microtubule is 25 nm and the plasma membrane is 9-11 nm thick, it is not possible for membrane-associated tubulin to assemble into a complete microtubule in the membrane environment. However, tubulin heterodimers may be able to function in the membrane environment as individual heterodimers or as polymers arranged into short protofilaments. At the cell membrane, membrane-associated tubulin may influence hormone-receptor interaction, receptor-G-protein coupling, and G-protein-effector coupling. Structural proteins, such as tubulin, can participate in cellular signaling by communicating through physical forces. By virtue of its interaction with the submembranous network of cytoskeletal proteins, tubulin, when perturbed in one locus, can transmit large changes in conformations to other points. Thus, GTP binding to membrane-associated tubulin might lead to a conformational change in either receptors or G proteins. This may, in turn, influence the binding of an agonist to its receptor. On the other hand, in the cell cytosol, subsequent to agonist-induced translocation of G-proteins from the membrane compartment to the cytosol, G-proteins may affect microtubule formation. In GH3 and AtT-20 cells (stably expressing TRH receptor), transiently transfected with Gq alpha cDNA, soluble tubulin levels decreased in Gq alpha-transfected GH3 and AtT-20 cells, by 33% and 52%, respectively. These results suggest that G-proteins may have a direct effect on the microtubule function in vivo. Because tubulin and G-protein families are ubiquitous and highly conserved, an interaction between these two protein families may occur in vivo, and this, in turn, can have an impact on signal transduction. However, the physiological significance of this interaction remains to be demonstrated.

Drugs that influence tubulin polymerization modulate thyrotropin-releasing hormone receptor number in AtT-20 cells

In order to examine the role of cytoskeleton in modulating the cell surface receptors, AtT-20 cells (stably expressing thyrotropin-releasing hormone receptors) were incubated with drugs that are known to modify the tubulin-microtubule system. The binding of [3H]methyl thyrotropin-releasing hormone ([3H]mTRH) to intact cells increased as a function of time, and was linear from 1.25 x 10(6) to 6.25 x 10(6) cells/ml. Cells incubated with colchicine, vinblastine, and taxol for 16 hr were harvested and the cell concentration was determined using a haemocytometer. Because the drugs inhibited the cell proliferation at 100 nM, it was decided to examine the effect of 100 nM of each of the three drugs on the ability of [3H]mTRH to bind cell surface receptors. Cells were incubated with the drugs for 16 hr at 37 degrees. After the incubation, cells (5 x 10(6) cells/ml) from each group were assayed for [3H]mTRH binding. Colchicine, vinblastine, and taxol stimulated [3H]mTRH binding by up to 27, 27, and 21%, respectively, without altering the Ka of the ligand to the receptor. These results suggest that perturbation of cytosolic microtubules leads to a reorganization of the spatial location of hormone receptors.

Modulation of the hepatic alpha 1-adrenoceptor responsiveness by colchicine: dissociation of free cytosolic Ca(2+)-dependent and independent responses

1. The cytoskeletal depolymerizing agent, colchicine, prevents the hepatic alpha 1-adrenoceptor-mediated stimulation of respiration, H+ and Ca2+ release to the effluent perfusate, intracellular alkalosis, and glycogenolysis. Unlike the other parameters, colchicine does not perturb the alpha 1-agonist-induced stimulation of gluconeogenesis or phosphorylase 'a' activation, and enhances the increase in portal pressure response. The lack of effect of colchicine on the hepatic alpha 2-adrenoceptor-mediated effects indicates that its actions are alpha 1-specific. 2. Colchicine enhances the acute alpha 1-adrenoceptor-mediated intracellular Ca2+ mobilization and prevents the activation of protein kinase C. This differential effect on the two branches of the alpha 1-adrenoceptor signalling pathway is a distinctive feature of the colchicine action. 3. The lack of effect of colchicine in altering the alpha 1-adrenoceptor ligand binding affinity suggests that it might interact with some receptor-coupled regulatory element(s). 4. The acuteness of the colchicine effect and the ability of its isomer beta-lumicolchicine to prevent all the alpha 1-adrenoceptor-mediated responses but the increase in vascular resistance, indicate that its action cannot be merely ascribed to its effects in depolymerizing tubulin. 5. Colchicine perturbs the hepatic responses to vasoactive peptides. It enhances the vasopressin-induced rise of cytosolic free Ca2+ in isolated hepatocytes and prevents the sustained decrease of Ca2+ in the effluent perfusate. It also inhibits the stimulation of glycogenolysis, without altering the stimulation of gluconeogenesis. 6. It is concluded that there are at least two major alpha 1-adrenoceptor signalling pathways. One is colchicine-sensitive, independent of variations in free cytosolic Ca2+, and protein kinase C-dependent; the other one is colchicine-insensitive, dependent on variations in free cytosolic Ca2+, and protein kinase C-independent.

Effects of vinblastine on cell membrane fluidity and the growth of SA-1 tumor in mice

Cell membranes can be targets of some anti-cancer drugs. Therefore, the purpose of this study was to determine whether vinblastine (VLB) can also affect the tumor cell membrane. On the in vivo SA-1 tumor model, alteration of cell membrane fluidity (measured by electron paramagnetic resonance, EPR), cytotoxicity and morphological changes of the SA-1 tumor cells after VLB treatment were studied. The cytotoxic effect of VLB was biphasic, with an initial fast increase in cytotoxicity followed by a plateau. The surviving cells had increased membrane fluidity and were morphologically changed. The dose-response curve of VLB on membrane fluidity was also biphasic with an initial fast increase in membrane fluidity followed by a plateau. Since dose-response curves of VLB cytotoxicity and its effect on membrane fluidity were similar, there was a high correlation between both effects. The effect of VLB on membrane fluidity was the most pronounced at 24 h and 48 h after treatment. The results of this study indicate that VLB affects cell membrane by increasing the membrane fluidity of SA-1 tumor cells in vivo in a dose-and time-dependent manner. Therefore, this finding may be beneficially implemented also in priming cells for other cytotoxic drugs and for appropriate timing of drug sequence in combined schedules.

Crystal-induced neutrophil activation. IV. Specific inhibition of tyrosine phosphorylation by colchicine

We recently demonstrated that pathologically relevant inflammatory microcrystals, namely triclinic monosodium urate (MSU) and calcium pyrophosphate dihydrate (CPPD) crystals, potently stimulate a characteristic protein tyrosine phosphorylation pattern in human neutrophils that differed from that observed in response to other soluble or particulate agonists. In this study, the effects of colchicine on protein tyrosine phosphorylation induced by MSU and CPPD crystals in human blood neutrophils were investigated. Immunoblot analysis with antiphosphotyrosine antibodies demonstrated that colchicine dose-dependently inhibited the tyrosine phosphorylation of all the proteins phosphorylated in response to MSU and CPPD crystals. Other microtubule-disruptive agents such as vinblastine, nocodazole, and colcemid also inhibited crystal-induced protein tyrosine phosphorylation while lumicolchicine and trimethylcolchicinic acid were without effect. Indomethacin and phenylbutazone were similarly without effect on microcrystal-induced tyrosine phosphorylation. Colchicine, as well as the other active alkaloids, failed to inhibit the protein tyrosine phosphorylation elicited by FMLP, C5a, leukotriene B4, and unopsonized zymosan. Overall, these results demonstrate that colchicine specifically and significantly inhibits the protein tyrosine phosphorylation induced by MSU and CPPD crystals and suggest that its effects are associated, at least in part, with its interaction with microtubules. Furthermore, the use of microtubule-disrupting drugs demonstrate that the mechanisms implicated in the induction of protein tyrosine phosphorylation by microcrystals differed from those involved in response to other soluble or particulate agonists.

Localization of serotonin-like immunoreactivity in the eyestalk of the prawn Palaemon serratus (Crustacea, Decapoda, Natantia)

A serotonin-like substance in the organ of Bellonci in the eyestalks of embryos, larvae, and adults of the prawn Palaemon serratus was visualized by the use of two specific antisera against serotonin (5-hydroxytryptamine; 5-HT) in combination with peroxidase-antiperoxidase (PAP). The organ of Bellonci, characterized by compact onion bodies distally and degenerating onion bodies proximally, was the only site of the serotonin-like substance in adults, as well as during development in embryos and larvae. Variations in the content of the 5-HT analogue in the adult were detected during the molting cycle. There was more immunoreactivity in specimens fixed at night than in those fixed in daytime. Likewise, colchicine and nialamide injections enhanced the immunoreactivity of the serotonin-like substance. Extirpations of the medulla externa X organ (MEX), a neurosecretory cell group of the optic ganglion medulla externa, produced the same effect.

Cellulose-microfibril-orienting mechanisms in plant cells walls

A brief review is given of the changing views over the years, as knowledge of wall structure has developed, concerning the mechanism whereby cellulose chains may be oriented. This leads to an examination of current concepts, particularly those concerning microtubules. It is shown that none of the mechanisms suggested whereby microtubules might cause orientation of cellulose microfibrils is consistent with the known range of molecular architectures found in plant cell walls. It is further concluded that any mechanism which necessitates an indissoluble link between the plasmalemma and the cellulose-synthesising complex at the tip of a microfibril is unacceptable. A new proposal is presented in which it is speculated that both microtubules and microfibrils are oriented by a mechanism separate from both. It is shown that if two vectors are contemplated, one parallel to cell length and one at right angles, and a sensor exists on the plasmalemma surface which responds to changes in the vectors, then all known wall structures may be explained. The possible nature of the vectors and the sensor are considered.

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.

Selective 1H-NMR relaxation investigations of membrane-bound drugs in vitro

Binding of colchicine to dipalmitoylphosphatidylcholine bilayer vesicles was detected by measuring the 1H-NMR selective spin-lattice relaxation rates of the low-field protons of colchicine. From the temperature dependence of the selective rates, preferential binding was observed above the temperature of transition. In the same way, binding of colchicine to red blood cells was detected and the equilibrium constant determined. Binding to the lipid matrix of red blood cells accounted only partially for the binding of colchicine to whole cells.

Colcemid treatment of myeloma prior to cell fusion increases the yield of hybridomas between myeloma and splenocyte

Effect of Colcemid treatment of myeloma (X63-Ag8-6.5.3.) prior to fusion with mouse spleen cell was studied in terms of hybridoma formation. Spleen cells from BALB/c mice immunized with various soluble antigens were fused with the myeloma cells by using polyethylene glycol solution. Colcemid treatment of myeloma cells prior to fusion increased the average number of hybridoma colonies per well by 26-570%. The yield of hybridomas producing antigen-specific antibodies was also higher with the Colcemid treatment. The results suggest that most of the proliferative hybridomas are formed by fusion of cells in the M-phase of the cell cycle.

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.

Lateral distribution of intramembrane particles in Purkinje and granule cells of the rat cerebellar cortex

The lateral distribution of intramembrane protein particles (IMP) in the plasma membrane of Purkinje and granule cells was quantitatively assessed in freeze-fracture replicas of the rat cerebellar cortex. In the plasma membrane of each cell type this technique showed domains with statistically significant differences in the distribution of IMP. The values were highly reproducible between different animals fixed in comparable conditions. This analysis provides an additional parameter (besides the number and size of IMP) in the assessment of neuronal membrane heterogeneity.

A rat monoclonal antibody reacting specifically with the tyrosylated form of alpha-tubulin. II. Effects on cell movement, organization of microtubules, and intermediate filaments, and arrangement of Golgi elements

A rat monoclonal antibody against yeast alpha-tubulin (clone YL 1/2; Kilmartin, J. V., B. Wright, and C. Milstein, 1982, J. Cell Biol., 93:576-582) that reacts specifically with the tyrosylated form of alpha-tubulin and readily binds to tubulin in microtubules when injected into cultured cells (see Wehland, J., M. C. Willingham, and I. V. Sandoval, 1983, J. Cell Biol., 97:1467-1475) was used to study microtubule organization and function in living cells. Depending on the concentration of YL 1/2 that was injected the following striking effects were observed: (a) When injected at a low concentration (2 mg IgG/ml in the injection solution), where microtubules were decorated without changing their distribution, intracellular movement of cell organelles (saltatory movement) and cell translocation were not affected. Intermediate concentrations (6 mg IgG/ml) that induced bundling but no perinuclear aggregation of microtubules abolished saltatory movement and cell translocation, and high concentrations (greater than 12 mg IgG/ml) that induced perinuclear aggregation of microtubules showed the same effect. (b) YL 1/2, when injected at intermediate and high concentrations, arrested cells in mitosis. Such cells showed no normal spindle structures. (c) Injection of an intermediate concentration of YL 1/2 that stopped saltatory movement caused little or no aggregation of intermediate filaments and no dispersion of the Golgi complex. After injection of high concentrations, resulting in perinuclear aggregation of microtubules, intermediate filaments formed perinuclear bundles and the Golgi complex became dispersed analogous to results obtained after treatment of cells with colcemid. (d) When rhodamine-conjugated YL 1/2 was injected at concentrations that stopped saltatory movement and arrested cells in mitosis, microtubule structures could be visualized and followed for several hours in living cells by video image intensification microscopy. They showed little or no change in distribution and organization during observation, even though these microtubule structures appeared not to be stabilized by injected YL 1/2 since they were readily depolymerized by colcemid or cold treatment and repolymerized upon drug removal or rewarming to 37 degrees C, respectively. These results are discussed in terms of the participation of microtubules in cellular activities such as cell movement and cytoplasmic organization and in terms of the specificity of YL 1/2 for the tyrosylated form of alpha-tubulin.

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.

In vivo effects of colchicine on milk fat globule membrane

Milk secretion in lactating goats was suppressed reversibly by infusing colchicine (2.5 to 5 mg) into one half of the udder via the teat canal. Fat globules were isolated from milks before, during and after (96 h post-infusion) this suppression. Protein, phospholipid, cholesterol (free and esterified), 5'-nucleotidase activity and peptide patterns by gel electrophoresis of these globule samples were determined. Association of [14C]colchicine with milk fat globules in vivo and in vitro also was investigated. Amounts of protein, phospholipid and free cholesterol per g of globule and 5'-nucleotidase per mg of globule protein fall following colchicine infusion. The nature of these changes suggests that the supply of membrane for milk secretion is restricted as a result of the drug treatment. Patterns of globule peptides by gel electrophoresis were qualitatively similar during the experimental period. However, a major globule glycoprotein, Mr = 52 000, showed a significant (3-fold) increase relative to the other principal peptide bands during the period of reduced milk flow. Analysis of milks for radioactivity following infusion of [14C]colchicine revealed that a portion of activity returning in milk is associated with fat globules. This activity peaked at 72 h post-infusion. Evaluation of [14C]colchicine binding to milk fat globules in vitro yielded evidence that the drug binds to the cytoplasmic, but not the exterior surface of the globule membrane. Colchicine's inhibition of milk synthesis and secretion is discussed.

Effect of colchicine and S,S,S-tributyl phosphorotrithioate (DEF) on the biliary excretion of sucrose, mannitol and horseradish peroxidase in the rat

The purpose of this study was to demonstrate the effect of colchicine and S,S,S-tributyl phosphorotrithioate (DEF) on vesicular transport of horseradish peroxidase (HRP) into bile at the same time that permeability changes occur in the canalicular membrane. Anesthetized Sprague-Dawley rats were surgically prepared with a bile duct cannulae. Four hours after colchicine pretreatment (10 mg/kg, i.p.), biliary excretion of intravenously injected sucrose and mannitol was increased, while that of HRP was decreased. Administration of these marker compounds from the bile side by segmented retrograde intrabiliary injection (SRII) (40 microliters washed in the 110 microliters saline) resulted in decreased biliary excretion of all three markers in colchicine-pretreated rats. Twenty minutes after DEF pretreatment by intrabiliary administration (40 microliters of DEF washed in with 31 microliters of saline and held in place for 0.5 min), the biliary excretion of intravenously injected sucrose and mannitol was decreased but that of HRP was increased; when administered by SRII, the biliary excretion of all three marker compounds was increased. These results demonstrate that colchicine, in addition to having blocked vesicular transport (HRP), also increased canalicular permeability to sucrose and mannitol. DEF, on the other hand, decreased canalicular permeability to sucrose and mannitol and enhanced vesicular transport of HRP.

Inhibition by colchicine of human lymphocytotoxic function: dependence on cell-bound drug level, spontaneous reversibility and antagonism by desacetylcolchicine (DAC)

Colchicine elicits inhibition of spontaneous, PHA-dependent and antibody-dependent forms of lymphocytotoxicity of peripheral blood lymphocytes (PBL) against allogeneic target cells. The findings are that it does so in cell-bound form and to near-maximum effect in the amount of this produced in PBL exposed to it at 10(-6)M concentration for 2 h at 37 degrees C. This represents only a small fraction of the cells' binding capacity, which suggests that it involves sites special in kind (localisation) rather than number (occupied at random). Desacetylcolchicine (DAC) (a known inhibitor of the colchicine-tubulin binding reaction) afforded the PBL protection at concentrations that antagonised the binding of colchicine to them. That DAC itself hardly inhibited PBL function is attributed by inference to a weaker binding affinity making for readier loss of it upon removal of the free drug. It did, however, exhibit a tight form of binding to other, functionally-insensitive cell sites not competed for by colchicine at 100-fold higher concentration. Contrary to the impression lent by other workers' studies (on mouse lymphocytes), colchicine-induced suppression of cytotoxic function is not necessarily irreversible. PBL cultured in drug-free medium gradually lost bound colchicine and they recovered in capacity to express spontaneous and PHA-dependent activity, but not in antibody-dependent activity. The residual cytolytic activity shown by colchicine pre-treated PBL appears in the case of antibody-dependent activity to be truly colchicine resistant; it survived unchanged a 10-fold increase in cell-bound drug level and it cannot be explained as a possible product of recovery. This colchicine-independence may reflect the existence of tubulin/microtubule-independent mechanisms contributing to antibody-dependent activity. Examination of colchicine-treated PBL for membrane fluidity changes, using the probe molecule DPH and the technique of fluorescence polarisation, has yielded negative results, even for cells treated at excessively high colchicine concentration (10(-4)M). All three forms of lymphocytotoxic activity were retained in PBL reconstituted after cryopreservation in liquid nitrogen.

Effect of colchicine on the uptake of prolactin and insulin into Golgi fractions of rat liver

In previous studies we have shown that 125I-labeled prolactin is taken up by a receptor-dependent process and concentrated in an intact form in Golgi elements from female rat liver (J. Biol. Chem., 1979, 254:209-214). In this study we have examined the effect of colchicine on this uptake process into Golgi elements. Colchicine [25 mumol (10 mg)/100 gm body wt] was injected intraperitoneally in adult female rats, and hepatic Golgi fractions were prepared at 1, 2, and 3 h postinjection. The enzyme recoveries and morphological appearance of fractions from colchicine-treated and control (alcohol alone) animals were similar. At times greater than 1 h after colchicine there was a marked (greater than 60%) inhibition of uptake of 125I-ovine prolactin (125I-oPRL) into Golgi light and intermediate fractions but no inhibition of uptake into Golgi heavy and plasmalemma elements. At times from 2 to 45 min postinjection, 125I-oPRL was extracted from Golgi elements and found to be largely intact as judged by rebinding to receptors. The inhibitory effect of colchicine was seen at doses ranging from 0.25 mumol to 25 mumol/100 g body wt. Vincristine also inhibited 125I-oPRL uptake into the Golgi light and intermediate fractions but lumicolchicine had no inhibitory effect. There was a smaller effect of colchicine both at early (1 h) and later (3 h) times on the extent and pattern of 125I-insulin uptake. Colchicine treatment did not produce a significant change in lactogen receptor levels in the Golgi fractions. These results demonstrate that colchicine treatment inhibited the transfer of prolactin into Golgi vesicular elements. The much smaller effect on insulin uptake suggests that there may be differences in the manner in which the two hormones are handled in the course of internalization.

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.

Primary hypoblast development in the chick : II. The role of cell division

Proliferative patterns in colchicine treated embryos during the first few hours of incubation, Eyal-Giladi and Kochav stages XI-XIII, clarify the role of cell division in the anterolateral expansion of the primary hypoblast as well as the expansion of the entire blastoderm. A layer of primary hypoblast (extra-embryonic endoderm) can form in the absence of cell division. Colchicine, in concentrations used here, does not prevent ingression of cells from the upper layer to the primary hypoblast and establishment of intercellular contacts. These processes, however modified, remain sufficiently operative so that a hypoblast layer forms. In addition, colchicine does not prevent radial expansion of the whole blastoderm. The demonstrated distribution of proliferative rates in the blastoderm can be the source of cells for blastoderm radial expansion, shape changes and for hypoblast development supplementing ingression of cells from the upper layer.

The arrangement of the Golgi complex beads is not controlled by the cytoskeleton

Exposure of insect fat body to treatments which disrupt microtubules (colchicine, vinblastine sulfate and cold treatment) blocks intracellular transport between the Golgi complex and the plasma membrane but does not affect Golgi complex bead rings or transport from rough endoplasmic reticulum to the Golgi complex. Drugs which disrupt microfilaments (cytochalasins B and D) do not affect the bead rings or intracellular transport of secretory proteins at any level. Thus, intracellular transport between the rough endoplasmic reticulum and the Golgi complex and the arrangement of the beads in rings are both independent of the cytoskeleton. The ring arrangement is presumably maintained by interconnection(s) with rough endoplasmic reticulum membrane.

An electron microscopic radioautographic study of collagen secretion in periodontal ligament fibroblasts of the mouse: II. Colchicine-treated fibroblasts

Colchicine administered intravenously depolymerized microtubules and disrupted the normal organization of the Golgi apparatus in periodontal ligament fibroblasts. Radioautography with 3H-proline indicated that collagen secretion was completely inhibited during a period of approximately 4 hours following the onset of the colchicine effect. During this period of secretory inhibition, labeled collagen precursors were present within a variety of dense bodies, primarily located in a juxtanuclear location replacing the normal Golgi complex. The time course of 3H-proline labeling from 2 to 8 hours suggested that small, newly formed dense bodies fused to form larger dense bodies and pleomorphic structures (zebra bodies), within which collagen precursors appeared to undergo partial polymerization. Autophagosomes, many labeled with 3H-proline, also increased in number after colchicine administration. A gradual decline in 3H-proline label occurred from 4 to 24 hours, presumably due to exocytosis of dense bodies or by the digestion of labeled collagen precursors within autophagosomes. These results support the concept that an intact microtubular network is essential for the organized transport of collagen precursors, from the rough endoplasmic reticulum to the Golgi apparatus, and the eventual transport and exocytosis of collagen secretory granules.

Microtubules: are they involved in the initiation of lymphocyte activation?

Purified human blood lymphocytes were stimulated with concanavalin A or phytohemagglutinin. DNA synthesis was measured with 2-h pulses of [3H]thymidine between 48 h and 73 h after stimulation. Colchicine, at concentrations between 0.1 muM and 10 muM, suppressed consequent DNA synthesis without affecting viability of the cells when added at any time up to 18 h before incorporation of [3H]thymidine was assessed. In concanavalin-A-stimulated lymphocytes, removal of the mitogen by methyl alpha-mannoside only prevented proliferation when added initially, but was without any effect when added after 20 h of stimulation, regardless of when DNA synthesis was measured. Thus, there was a period after 20 h of concanavalin A stimulation, when DNA synthesis was still sensitive to colchicine, but no longer required the presence of the mitogen. Colchicine also suppressed incorporation of [3H]leucine into protein, in resting as well as mitogen-stimulated lymphocytes. Similarly, colchicine decreased amino acid transport, as determined by uptake of alpha-amino-isobutyrate, which appeared to be the rate-limiting step in the incorporation of amino acids into protein in colchicine-treated cells. When the rate of protein synthesis was followed by the relative distribution of ribosomal particles, especially the increase of polysomes in activated lymphocytes, colchicine was without any detectable effect. The early increase in the incorporation of [14C]oleate into phospholipids was identical in the presence or absence of the microtubule-active drug. The data strongly suggest that microtubules are not involved in the initiation of lymphocyte growth or mitogenesis.

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.

A colchicine-sensitive uptake system in Morris hepatomas

The interference of microtubular disruptors with the uptake of amino acids and other low molecular weight substrates has been studied in Morris hepatomas, host liver, and regenerating liver. Colchicine inhibits amino acid transport (alpha-aminoisobutyric acid, L-methionine, and L-leucine) in hepatomas by 59-98% whereas transport in host and regenerating liver is not impeded but increased. In hepatomas, treatment urea, and carbonate. Vinblastine, but not lumicolchicine or cytochalasin B, is an effective inhibitor. The inhibition of uptake is not linked to a decrease of cellular ATP and UTP. The data suggest that the transport of low molecular weight substrates in hepatomas is related to microtubules or other colchicine-binding structures, e.g., of the plasma membrane. This colchicine-sensitive uptake system in hepatomas may be due to the malignant transformation of hepatocytes.

Evidence that microtubules play a permissive role in hepatocyte very low density lipoprotein secretion

To determine whether a minimum number of assembled microtubules is required for very low density lipoprotein (VLDL) triglyceride TG) secretion in hepatocytes, antimicrotubule drugs of different concentrations were given to rats. Hepatic VLDL-TG release was subsequently measured by a liver perfusion system, and hepatocyte ultrastructural changes were analyzed by quantitative ultrastructural methods. The results demonstrate a tight coupling between the reduction in hepatocyte microtubule content and the reduction in hepatic VLDL-TG secretion which is related to the dose of colchicine or vinblastine administered. The various estimates imply that a minimum number of microtubules is necessary for hepatic VLDL secretion to proceed normally and that hepatic VLDL secretion rates reach their nadir (10--30% of control) when microtubules comprise less than 0.005% of the cytoplasm (or less than 10% of control values) when microtubules comprise less than 0.005% of the cytoplasm (or less than 10% of control values). At this point, hepatocyte Golgi complexes are also greatly altered; Golgi complexes with recognizable dictyosomal membranes are reduced to 15% of control values and the region is filled with large numbers of electron-dense bodies which appear to be lysosomes in the process of digesting VLDL. There is a predilection for the remaining Golgi complexes to be associated with a few segments of microtubules, even when no microtubules can be measured in random samplings of hepatocytes. Clusters of vacuoles containing VLDL are also present throughout the cytoplasm; the limiting membranes of 25% of these vacuoles are studded with ribosomes. These findings demonstrate that the administration of antimicrotubule agents results in decreases in hepatic VLDL-TG secretion which are associated with loss of microtubules and alteration of existing Golgi complexes.

The dynamics of membrane structure

The membranes of living organisms are involved in many aspects of the life, growth and development of all cells. The predominant structural elements of these membranes are lipids and proteins and the basic strucvture of these molecules has been reviewed. The physical properties of the lipid constituents particularly their behavior in aqueous systems has led to the concepts of thermotropic and lyotropic mesomorphism; the interaction between different types of lipid molecules modulate this behavior. Interaction of phospholipids in aqueous systems with cholesterol, ions and drugs have been examined in this context. In addition a variety of model lipid-protein systems have been investigated and the implications of interactions between lipids and different proteins in biological membranes has been evaluated. This leads to a detailed consideration of the way lipids and proteins ae organized in cell membranes and contains an appraisal of the evidence supporting contemporary views of membrane structure. Particular attention has been devoted to the question of how mobile the components are within the structure. Particular attention has been devoted to the question of how mobile the components are within the structure. Finally the biosynthesis, turnover and modulation of the properties of interacting membrane constituents is critically reviewed and possible ways of controlling the behavior of cells and organisms by altering the structural parameters of different membranes has been considered.

Lipid composition and microviscosity of subcellular fractions from rabbit thymocytes. Differences in the microviscosity of plasma membranes from subclasses of thymocytes

There are indications from freeze-fracture experiments that subclasses of rabbit thymocytes show different mobilities of plasma membrane components. Consequently, one would expect differences in the fluidity of the plasma membrane. For this reason, rabbit thymocytes were separated on a Ficoll/Metrizoate gradient yielding three subclasses representing various levels of cell differentiation. These thymocyte subclasses did not show any significant differences in the degree of fluorescence polarization using the probe 1,6-diphenyl-1,3,5-hexatriene. The fluorescence polarization of the plasma membrane may be overshadowed by the contribution of all cellular lipids due to penetration of the fluorescent probe into the cell. Therefore, plasma membranes were isolated from rabbit thymocytes using a cell-disrupting pump, differential centrifugation, and sucrose density gradient centrifugation. As shown by biochemical and electron microscopical analyses, plasma membranes with a high degree of purity were obtained. As expected the plasma membrane fractions showed a higher microviscosity than the other subcellular fractions. This was attributed to a higher cholesterol to phospholipid molar ratio and a higher degree of saturation of phospholipid fatty acid chains. Subsequently, the microviscosity was measured of plasma membrane preparations obtained from two main subclasses of thymocytes representing mature and immature lymphocytes. The immature thymocytes yielded two plasma membrane fractions with higher microviscosity than the mature cells. These finding is in line with earlier observed differences in the glycerol-induced clustering of intramembranous particles. Furthermore, the results of this study support the view that the fluorescence polarization technique applied to whole cells does not exclusively monitor the plasma membrane.

Effects of drugs that influence eucaryotic motile processes on motility of Cystobacter fuscus (Myxobacterales)

Cytochalasin B, dbcAMP and EGTA were found to inhibit the motility of Cystobacter fuscus completely whereas colchicine and cAMP only reduced velocity of movement.

The role of microtubules and cell-wall deposition in elongation of regenerating protoplasts of Mougeotia

Protoplasts of the filamentous green alga Mougeotia sp. are spherical when isolated and revert to their normal cylindrical cell shape during regeneration of a cell wall. Sections of protoplasts show that cortical microtubules are present at all times but examination of osmotically ruptured protoplasts by negative staining shows that the microtubules are initially free and become progressively cross-bridged to the plasma membrane during the first 3 h of protoplast culture. Cell-wall microfibrils areoobserved within 60 min when protoplasts are returned to growth medium; deposition of microfibrils that is predominantly transverse to the future axis of elongation is detectable after about 6 h of culture. When regenerating protoplasts are treated with either colchicine or isopropyl-N-phenyl carbamate, drugs which interfere with microtubule polymerization, they remain spherical and develop cell walls in which the microfibrils are randomly oriented.