Stabilizing effects of D2O on the microtubular components and needle-like form of heliozoan axopods: a pressure-temperature analysis

The T1R3 subunit of the sweet taste receptor is activated by D2O in transmembrane domain-dependent manner

Deuterium oxide (D2O) is water in which the heavier and rare isotope deuterium replaces both hydrogens. We have previously shown that D2O has a distinctly sweet taste, mediated by the T1R2/T1R3 sweet taste receptor. Here, we explore the effect of heavy water on T1R2 and T1R3 subunits. We show that D2O activates T1R3-transfected HEK293T cells similarly to T1R2/T1R3-transfected cells. The response to glucose dissolved in D2O is higher than in water. Mutations of phenylalanine at position 7305.40 in the transmembrane domain of T1R3 to alanine, leucine, or tyrosine impair or diminish activation by D2O, suggesting a critical role for T1R3 TMD domain in relaying the heavy water signal.

Heavy Water Affects Vital Parameters of Human Melanoma Cells in vitro

Purpose

Although regular water is composed of two hydrogens and one oxygen, referred to as H₂O, a small amount of water on this planet contains alternative forms of elements with different molecular weights because of the addition of neutrons. The present study was dedicated to studying the effect of heavy water (D₂O), in which the two hydrogens become substituted by deuterium, on the cell physiology of different human cells with particular focus on malignant melanoma cells.

Methods

Cells were cultured in regular medium in which the content of H₂O was gradually substituted by D₂O or deuterium-depleted water (DDW). Following this, the changes of basic cellular parameters, such as morphology, migration, proliferation, cell cycle, apoptosis and microtubule integrity were examined.

Results

It was found that raising the D₂O content above the standard levels led to a concentration-dependent decrease in proliferation. Lowering the D₂O levels below this level had no effect. Likewise, elevated D₂O levels hampered migration. Moreover, cell-cycle analysis showed an increase of sub-G1 cells. Corroboratively, markers for apoptosis were induced (histone-associated DNA fragments, Bax, and PARP). In regard to microtubule integrity, only very high levels of D₂O (75%) caused partial filament condensation.

Conclusion

D₂O, although chemically identical with H₂O, shows proapoptotic and antiproliferative effects on melanoma cells. These findings give a closer look of this interesting compound.

Heavy Water (D2O) Containing Preservation Solution Reduces Hepatic Cold Preservation and Reperfusion Injury in an Isolated Perfused Rat Liver (IPRL) Model

Background: Heavy water (D₂O) has many biological effects due to the isotope effect of deuterium. We previously reported the efficacy of D₂O containing solution (Dsol) in the cold preservation of rat hearts. Here, we evaluated whether Dsol reduced hepatic cold preservation and reperfusion injury. Methods: Rat livers were subjected to 48-hour cold storage in University of Wisconsin (UW) solution or Dsol, and subsequently reperfused on an isolated perfused rat liver. Graft function, injury, perfusion kinetics, oxidative stress, and cytoskeletal integrity were assessed. Results: In the UW group, severe ischemia and reperfusion injury (IRI) was shown by histopathology, higher liver enzymes leakage, portal resistance, and apoptotic index, oxygen consumption, less bile production, energy charge, and reduced glutathione (GSH)/oxidized glutathione (GSSG) ratio (versus control). The Dsol group showed that these injuries were significantly ameliorated (versus the UW group). Furthermore, cytoskeletal derangement was progressed in the UW group, as shown by less degradation of α-Fodrin and by the inactivation of the actin depolymerization pathway, whereas these changes were significantly suppressed in the Dsol group. Conclusion: Dsol reduced hepatic IRI after extended cold preservation and subsequent reperfusion. The protection was primarily due to the maintenance of mitochondrial function, cytoskeletal integrity, leading to limiting oxidative stress, apoptosis, and necrosis pathways.

Deuterium oxide protects against myocardial injury induced by ischemia and reperfusion in rats

Objectives. Although deuterium oxide (D₂O) has preservative property on the extracted organ, whether D₂O also protects the in situ myocardial injury remains unknown. Using cardiac microdialysis, local administration of D₂O through dialysis probe was applied in situ rat heart. We examined the effect of the D₂O on the myocardial injury induced ischemia, reperfusion, and chemical hypoxia. Methodology. We measured dialysate myoglobin levels during 30 min of coronary occlusion and reperfusion in the absence and presence of D₂O. Furthermore, to confirm the effect of D₂O on NaCN induced myocardial injury, we measured the dialysate myoglobin levels with local perfusion of NaCN in the absence and presence of D₂O. Results. The dialysate myoglobin levels increased from 177 ± 45 ng/mL at baseline to 3030 ± 1523 ng/mL during 15-30 min of coronary occlusion and further increased to 8588 ± 1684ng/mL at 0-15 min of reperfusion. The dialysate myoglobin levels with 60 min local perfusion of NaCN increased to 1214 ± 279 ng/mL. D₂O attenuated myocardial myoglobin release during 15-30 min of coronary occlusion and 0-30 min of reperfusion and 15-60 min of local perfusion of NaCN. Conclusions. D₂O might have a beneficial effect of myocardium against ischemia, reperfusion and chemical hypoxia.

Successful transplantation of rat hearts subjected to extended cold preservation with a novel preservation solution

Since prolonged cold preservation of the heart deteriorates the outcome of heart transplantation, a more protective preservation solution is required. We therefore developed a new solution, named Dsol, and examined whether Dsol, in comparison to UW, could better inhibit myocardial injury resulting from prolonged cold preservation. Syngeneic heterotopic heart transplantation in Lewis rats was performed after cold preservation with UW or Dsol for 24 or 36 h. In addition to graft survival, myocardial injury, ATP content, and Ca(2+) -dependent proteases activity were assessed in the 24-h preservation group. The cytosolic Ca(2+) concentration of H9c2 cardiomyocytes after 24-h cold preservation was assessed. Dsol significantly improved 7-day graft survival after 36-h preservation. After 24-h preservation, Dsol was associated with significantly faster recovery of ATP content and less activation of calpain and caspase-3 after reperfusion. Dsol diminished graft injury significantly, as revealed by the lower levels of infarction, apoptosis, serum LDH and AST release, and graft fibrosis at 7-day. Dsol significantly inhibited Ca(2+) overload during cold preservation. Dsol inhibited myocardial injury and improved graft survival by suppressing Ca(2+) overload during the preservation and the activation of Ca(2+) -dependent proteases. Dsol is therefore considered a better alternative to UW to ameliorate the outcome of heart transplantation.

Deuteration as a tool in investigating the role of protons in cell signaling

BACKGROUND

The mechanisms underlying the inhibitory effects of deuterium oxide (D₂O; heavy water) are likely to provide insight into the fundamental significance of hydrogen bonds in biological functions. Previously, to begin elucidating the effect of D₂O on physiological functions in living cells, we studied the effects of D₂O on voltage-sensitive Ca²(+) channels in AtT 20 cells and showed that actin distribution, Ca²(+) currents, and β-endorphin release were affected. However, the molecular mechanisms underlying the inhibitory effects of D₂O in whole animals and living cells remain obscure, especially in the effects of D₂O on the cell signaling.

METHODS

We investigated the molecular mechanisms underlying the inhibitory effects of D₂O on the IP₃-mediated Ca²(+) signaling pathway using Ca²(+) imaging and micro-calorimetric measurements in mGluR1-expressing CHO cells.

RESULTS

DHPG-induced Ca²(+) elevations were markedly reduced in D₂O. Moreover, the Ca²(+) elevations were completely suppressed in H₂O after receptor activation with DHPG in D₂O, recovering gradually in H₂O medium. Without prior stimulation in D₂O, however, DHPG-induced Ca²(+) elevations in H₂O were not affected. Micro-calorimetric measurements showed reduced total DHPG-evoked heat generation in D₂O, while initial heat production and absorption associated with receptor activation were found to be larger. The reduction of DHPG-induced Ca²(+) elevation and heat generation in D₂O medium may be due to decreased amount of IP₃ by the reduced hydrolysis of PIP₂.

GENERAL SIGNIFICANCE

Protein structure changes due to the replacement of hydrogen with deuterium will induce the inhibitory effects of D₂O by reduction of the frequency of -OH bonds.

Increased expression of Hsp70 for resistance to deuterium oxide in a yeast mutant cell line

Labeling with stable isotopes, typically deuterium (D), is powerful tool for studying the functional structure of biomolecules by NMR. Biosynthesis of certain deuterated proteins in microorganisms cultured in deuterium oxide (D(2)O) is an attractive strategy. However, the growth of almost all microorganisms is inhibited at high concentrations of D(2)O. We isolated a mutant of yeast that grows well in D(2)O. The expression of Hsp70 was enhanced in the mutant. The increased expression also endowed the yeast with cold-resistance. The mutant might be useful for biosynthesis of D-labeled biomolecules.

Pharmacological uses and perspectives of heavy water and deuterated compounds

Since the discovery of D2O (heavy water) and its use as a moderator in nuclear reactors, its biological effects have been extensively, although seldom deeply, studied. This article reviews these effects on whole animals, animal cells, and microorganisms. Both "solvent isotope effects," those due to the special properties of D2O as a solvent, and "deuterium isotope effects" (DIE), which result when D replaces H in many biological molecules, are considered. The low toxicity of D2O toward mammals is reflected in its widespread use for measuring water spaces in humans and other animals. Higher concentrations (usually >20% of body weight) can be toxic to animals and animal cells. Effects on the nervous system and the liver and on formation of different blood cells have been noted. At the cellular level, D2O may affect mitosis and membrane function. Protozoa are able to withstand up to 70% D2O. Algae and bacteria can adapt to grow in 100% D2O and can serve as sources of a large number of deuterated molecules. D2O increases heat stability of macromolecules but may decrease cellular heat stability, possibly as a result of inhibition of chaperonin formation. High D2O concentrations can reduce salt- and ethanol-induced hypertension in rats and protect mice from gamma irradation. Such concentrations are also used in boron neutron capture therapy to increase neutron penetration to boron compounds bound to malignant cells. D2O is more toxic to malignant than normal animal cells, but at concentrations too high for regular therapeutic use. D2O and deuterated drugs are widely used in studies of metabolism of drugs and toxic substances in humans and other animals. The deuterated forms of drugs often have different actions than the protonated forms. Some deuterated drugs show different transport processes. Most are more resistant to metabolic changes, especially those changes mediated by cytochrome P450 systems. Deuteration may also change the pathway of drug metabolism (metabolic switching). Changed metabolism may lead to increased duration of action and lower toxicity. It may also lead to lower activity, if the drug is normally changed to the active form in vivo. Deuteration can also lower the genotoxicity of the anticancer drug tamoxifen and other compounds. Deuteration increases effectiveness of long-chain fatty acids and fluoro-D-phenylalanine by preventing their breakdown by target microorganisms. A few deuterated antibiotics have been prepared, and their antimicrobial activity was found to be little changed. Their action on resistant bacteria has not been studied, but there is no reason to believe that they would be more effective against such bacteria. Insect resistance to insecticides is very often due to insecticide destruction through the cytochrome P450 system. Deuterated insecticides might well be more effective against resistant insects, but this potentially valuable possibility has not yet been studied.Key words: deuterium, heavy water, D2O, deuterium isotope effects.

Germination of Nosema algerae (Microspora) spores: conditional inhibition by D2O, ethanol and Hg2+ suggests dependence of water influxupon membrane hydration and specific transmembrane pathways

The germination of microsporidian spores under conditions expected to affect water flow across the plasma membrane-wall complex was studied by assessing their responses to in vitro stimulation with Na+ or K+. Partial or full substitution of common water with D2O, which more effectively coats ions and electrostatically-charged cell surfaces with relatively stable hydration layers, delayed and inhibited spore germination in a concentration-dependent manner; yet, preincubation in 100% D2O did not change the normal response to standard stimulation. Water structure-breaking conditions, such as an increase in temperature (within the 15 degrees C to 40 degrees C range) or in ionic strength (1- to 10-fold normal), opposed the inhibition by D2O and allowed significant stimulation by Li+, the monovalent cation with the largest hydration diameter and a usually weak stimulant action on the spores. Ethanol, known to reduce water permeation across cell membranes and phospholipid bilayers, also caused a powerful and dose-dependent (1% to 4% v/v) inhibition of spore germination, but pretreatment with ethanol did not affect the normal response. HgCl2, an inhibitor of specific water channels, blocked spore germination at just 250 microM in the normal stimulation solution irrespective of the temperature, and permitted only a delayed response in high salt stimulation solutions. However,the inhibition by Hg2+ was abolished by the simultaneous presence of 2-mercaptoethanol in the medium. These results suggest (1) that spore germination is keenly dependent upon the hydration states of both the plasma membrane-wall complex and the stimulant ions, and (2) that osmotic water flows into the spores through specific transmembrane pathways with critical sulfhydryl groups, i.e., analogous to the water channels that facilitate water movements across the plasma membranes of highly permeable cells.

Regulation of CD18 expression in human neutrophils as related to shape changes

The study analyses the distribution and quantitative expression of surface CD18 of neutrophils exposed to distinct stimuli that produce different types of continuous shape changes, including types that are associated with locomotion and others that are not. The chemotactic peptide N-formyl-L-norleucyl-L-leucyl-L-phenylalanine, colchicine and nocodazole were used to induce a polarized locomotor morphology, phorbol myristate acetate, 1,2-dioctanoylglycerol and 1-oleoyl-2-acetyl-glycerol to induce non-polar motile cells ruffling all over the surface and 2H2O to induce non-polar cells performing circus movements as have been previously described. Except for colchicine and nocodazole, these stimuli increased surface expression of CD18. Thus, stimulated shape changes are frequently, though not always, associated with increased surface expression of CD18. High concentrations (10(−7) to 10(−5) M) of phorbol myristate acetate but not of chemotactic peptide induced down-regulation of surface CD18. Cytochalasin D (10(−4) M) stimulated CD18 expression even though it inhibited shape changes. The surface distribution of CD18 determined by light microscopy was uniform in unstimulated cells or in various forms of stimulation except for cells treated with 10(−5) M cytochalasin D. Cytochalasin D (10(−5) M) produced CD18 accumulation at the pole opposite the F-actin cap. Experiments with colchicine, nocodazole, 2H2O and cytochalasin D suggest that microtubules as well as microfilaments modulate surface expression of CD18. The results suggest that protein kinase C and phosphatases play a role in regulating surface expression of CD18 in neutrophils.(ABSTRACT TRUNCATED AT 250 WORDS)

Microtubule dissassembly in vivo: intercalary destabilization and breakdown of microtubules in the heliozoan Actinocoryne contractilis

In the marine heliozoan Actinocoryne contractilis, uninterrupted rods of microtubules stiffen the axopodia and the stalk. Stimulation in sea water elicits an extremely fast contraction (millisecond range) accompanied by almost complete Mt dissociation. Using high-speed cinematography and light transmittance measurements, we have studied the process of Mt disassembly in real time. In sea water, Mt disassembly follows an exponential decrease (mean half time of 4 ms) or proceeds by short steps. Cell contraction and Mt disassembly have been inhibited or slowed down through the use of artificial media. Although kinetics are slower (mean half time of 3 s), the curves of the length change against time look similar. The rapid as well as the slower process are accompanied by the formation of breakpoints on the stalk, from which disassembly proceeds. In specimens fixed during the slowed contraction, the presence across the Mt rods, of a single or multiple destabilization band that may consist of granular material and polymorphic forms of tubulin supports the hypothesis of "intercalary destabilization and breakdown" of axonemal Mts.

Isolation and properties of the axopodial cytoskeleton of a heliozoan, Echinosphaerium akamae

The axopodia of a large heliozoan, Echinosphaerium akamae, were efficiently liberated from the cell body by treatment with 65% D(2)O solution containing 5 mM MgCl(2),2.1 mM EGTA, 1 mM KCl and 5 mM HEPES (pH 6.9). After D20 treatment, the cell bodies were removed by centrifugation at a low speed for 30 sec and the resulting supernatant was recentrifuged at 10,000 × g for 10 min. The axopodia were obtained as the pellet fraction without any contamination from the cell body. The isolated axopodia maintained their regular arrangement of cytoskeletal microtubules and were shortened by treatment with Ca(2+). When the isolated axopodia was subjected to SDS-polyacrylamide gel electrophoresis, two major protein bands were detected. The molecular weights of the proteins, tentatively identified as the heliozoan tubulins, were estimated to be about 46 and 50 kD, and an antibody against rat brain tubulin reacted with only the 46 kD protein species.

Characterisation of IgE-mediated histamine release from equine basophils in vitro

In vitro IgE-mediated histamine release by equine blood basophils was characterised as the basis for a screening test for immediate hypersensitivity responses in horses. The responses are initiated by inducing agents that are capable of crosslinking or bridging the membrane-bound IgE molecules. The release process is complete within 40 mins. In vitro histamine release is dose-dependent, with a submaximal response at less or greater than the optimal dose of inducing agent. Exogenous calcium is required but not magnesium; the optimal release calcium concentration is 1.0 to 1.5 mM. If an IgE-mediated inducing agent is added in the absence of exogenous calcium, the basophils become desensitised. The pH and temperature optima for release are physiological (pH 7.4, 37 degrees C). Histamine release is potentiated by deuterium oxide.

Modulation of the effect of histamine-releasing lymphokine on human basophils

Agents which increase or mimic intracellular cyclic 3',3'-adenosine monophosphate (cAMP) - theophylline dibutyryl cAMP (DBcAMP) and isoprenaline (in the presence of theophylline) - all produced pronounced inhibition of histamine release from human basophils, thus suggesting a regulatory role for the cAMP system. The effect of the flavonoids , quercetin and taxifolin , and the structurally-related cromone disodium cromoglycate (DSCG) was also studied. Only quercetin was effective in inhibiting histamine release. This is similar to the situation in IgE-mediated release. The microtubule stabilizer, deuterium oxide (D2O), at a concentration of 44% caused up to three-fold increase in release. This supports the belief that histamine release by this histamine-releasing factor ( HRF ) is a secretory process. Indomethacin and 5,8,11,14-eicosatetraynoic acid (ETYA), which are modulators of arachidonic acid metabolism, produced little or no inhibition of histamine release by HRF , thus suggesting that the release is largely independent of the arachidonate system, probably unlike IgE-mediated release.

Effect of microtubule-disrupting agents on superoxide production in human polymorphonuclear leukocytes

We explored the effects of compounds known or proposed to affect microtubule functions on superoxide (O2-) production in human polymorphonuclear leukocytes stimulated by N-formyl-methionyl-phenylalanine (f-Met-Phe), calcium ionophore A23187 and phorbol myristate acetate. F-Met-Phe-induced O2- production was markedly potentiated not only by microtubule-disrupting agents, including colchicine, vincristine, vinblastine, nocodazole, podophyllotoxin and griseofulvin, but also deuterium oxide (2H2O), which is proposed to stabilize microtubules, and not affected by lumicolchicine. Ionophore A23187-induced O2- production was not influenced by colchicine, and markedly enhanced by 2H2O, whereas phorbol myristate acetate-induced O2- production was not influenced by colchicine, and slightly inhibited by 2H2O. 2H2O did not counteract the effects of colchicine and vice versa. Dibutyryl cyclic AMP and prostaglandin E1 inhibited O2- production stimulated by f-Met-Phe and ionophore A23187, whereas phorbol myristate acetate-induced O2- production was strongly resistant to the inhibitory effect of these agents. The enhancing effect of colchicine and 2H2O on f-Met-Phe-induced O2- production was abolished by dibutyryl cyclic AMP. Colchicine promoted concanavalin A cap formation, and 2H2O produced concanavalin A patch formation, whereas dibutyryl cyclic AMP did not affect the distribution of concanavalin A receptors. In addition, 2H2O and dibutyryl cyclic AMP did not interfere with the colchicine-induced concanavalin A cap formation. These findings suggest that f-Met-Phe, ionophore A23187 and phorbol myristate acetate may activate the oxidative metabolism of human polymorphonuclear leukocytes through different mechanisms, and that microtubule-disrupting agents, 2H2O and cyclic AMP agonists may affect the different steps of the activating system of NAD(P)H oxidase.

The interaction of sodium nitroprusside with human endothelial cells and platelets: nitroprusside and prostacyclin synergistically inhibit platelet function

Sodium nitroprusside (NP) is a potent vasodilator that also inhibits platelet aggregation. To test the hypothesis that NP causes both of these effects by altering the balance between prostacyclin (PGI2) produced by endothelial cells and thromboxane A2 (TXA2) produced by platelets, we incubated each of these cell types with NP for 5 minutes and assayed the PGI2 and TXA2 produced. NP at pharmacologically achieved doses (0.01--30 micrograms/ml) inhibited platelet aggregation and resultant TXA2 synthesis in a dose- and time-dependent manner (p less than 0.001). The inhibition was not dependent on cAMP production, external calcium concentration, or suppression of TXA2 synthesis. NP did not alter the production of PGI2 by cultured human endothelial cells as measured by radioimmunoassay for 6-Keto-PGF1 alpha, the stable hydrolysis product of PGI2. However, supernates of NP-treated endothelial cells containing low, noninhibitory concentrations of NP unexpectedly inhibited platelet aggregation. This inhibition of platelet aggregation was due to synergy between PGI2 (0.1--3 nM) and NP (p interaction less than 0.03). The synergistic inhibition by NP and PGI2 of platelet aggregation and TXA2 synthesis in vivo may explain some of the beneficial actions of NP in the treatment of hypertension and congestive heart failure.

Effect of deuterium oxide on neutrophil oxidative metabolism, phagocytosis, and lysosomal enzyme release

We have previously shown that deuterium oxide (D2O) enhances the oxidation of methionine, a myeloperoxidase (MPO) -mediated reaction, by human neutrophils during phagocytosis. However, D2O has no effect on the oxidation of methionine by the purified MPO-H2O2-Cl- system. To explain this observation, we studied the effect of D2O on the oxidative metabolism, phagocytosis, and lysosomal enzyme release by human neutrophils. D2O stimulated the hexose monophosphate shunt (HMS) activity of resting neutrophils in a dose-response fashion. In the presence of latex particles or phorbol myristate acetate (PMA), D2O brought about an exaggerated stimulation of the HMS activity. This enhancement of the HMS activity by D2O was markedly reduced when neutrophils form two patients with X-linked chronic granulomatous disease (CGD) were used, either in the presence or absence of latex particles or PMA. Superoxide and H2O2 production by neutrophils in the presence of latex particles or PMA were also stimulated by D2O. In contrast, D2O inhibited the ingestion of latex particles. D2O enhanced the extracellular release of MPO, but not lactate dehydrogenase, by neutrophils only in the simultaneous presence of cytochalasin B and latex particles. The enhancement of HMS activity and MPO release by D2O was partially inhibited by colchicine. Our results suggest that enhancement of neutrophil oxidative metabolism by D2O may in part explain the stimulation of methionine oxidation by phagocytosing neutrophils.

Superoxide anion-generating activities of macrophages as studied by using cytochalasin E and lectins as synergistic stimulants for superoxide release

Treatment of macrophages with cytochalasin E in combination with a lectin was found to stimulate the generation of superoxide anions (O2-) very efficiently. The macrophages stimulated with concanavalin A, phytohemagglutinin or wheat germ agglutinin released superoxide, but cells pretreated with cytochalasin E released much greater amounts of superoxide, without notable lag time, upon stimulation with the lectin. Wheat germ agglutinin was found to be the most efficient stimulant among the lectins tested. Superoxide generation in guinea pig macrophages was shown to be dependent largely on cytoplasmic glucose metabolism and to some extent on mitochondrial respiration, since the superoxide release was largely but not totally inhibited by 2-deoxyglucose and to a lesser extent by antimycin A or KCN. The method presented is sensitive and allows rapid assay of the superoxide-generating activity with only 1--5 X 10(5) macrophages for a single determination. In application of this technique, elevation of the superoxide-generating activity was shown with macrophages elicited by chemical inflammation or those obtained from mice after treatment with tubercle bacilli.

Photomechanical migrations of pigment granules along the retinula cells of the crayfish

The light-dependent migrations of proximal pigment granules along the photoreceptors of the crayfish compound-eye were studied in isolated retinas and eyestalks. The extent and kinetics of movement in each direction were found quantitatively equivalent to those observed in the organ in situ. These and other features make these cells to appear as intrinsically independent pigmentary effectors, directly responsive to light. During dark adaptation (DA) the pigment migrates away from the cell nucleus and accumulates along the axon in two distinct steps. Each step constitutes half of the total distance of about 180 microns and proceeds at 0.30 micron/sec. Only prolonged metabolic impairment inhibited the first phase, while the second was blocked by hypoxia, cyanide, colchicine, and D2O. The maintenance of a full DA position was also shown to be highly dependent upon metabolism. Light incidence on DA eyes is followed by an apparently monophasic expansion of the pigment from the axon towards the perikaryl region at 0.38 micron/sec. This movement was not affected by any of the foregoing agents and seems to be a passive relaxation process. Cytochalasin B had no effect on either motion. The migration in either direction has an exponential time course and is temperature dependent. Electron microscopy revealed two separate patterns of cytoplasmic organization corresponding to the cell areas where the two phases of DA occur. In the region close to the nucleus the pigment appears irregularly scattered, whereas in the axon the granules are situated arond a thick longitudinal bundle of microtubules. These results suggest the existence of two different mechanisms of pigment granule translocation operating in two separate regions of the retinula cell.

Enhancement of macrophage adenylate cyclase by microtubule disrupting drugs

The accumulation of cyclic adenosine 3',5'-monophosphate (cAMP) in guinea-pig macrophages exposed to the adenylate cyclase (AC) stimulators prostaglandin E1 (PGE1) and isoproterenol (IP), was markedly enhanced by pretreatment of the cells with colchicine, vinblastine, and podophyllotoxin--agents which prevent microtubule assembly. The same agents did not augment basal cAMP levels. The facilitating effect of the drugs on the response to PGE1 and IP developed both in the absence and presence of a phosphodiesterase (PDE) inhibitor. The same drugs also enhanced the accumulation of cAMP induced by cholera toxin (CT) but the presence of a PDE inhibitor was required for such enhancement to become evident. Pretreatment of macrophages with cytochalasin B, an agent interfering with microfilament function, had no effect on the responsiveness of the cells to AC stimulators. The microtubule stabilizer, deuterium oxide (D2O) partially reversed the colchicine effect. Microtubule disrupting drugs did not block the release of cAMP from the cells into the surrounding medium. Macrophages incubated as monolayers or in suspension showed the same degree of increased responsiveness to stimulators after preexposure to colchicine. Preincubation with the ionophore A23187, which elevates the intracellular concentration of Ca2+, also enhanced the stimulation of AC by PGE1 and IP. Microtubule disrupting agents did not potentiate AC activity in broken cell preparations, whether added to the intact cells before disruption or directly to the enzyme assay mixture, nor did they affect PDE activity of macrophage sonicates. Moderate enhancement of PGE1-induced cAMP formation was also seen in colchicine- and vinblastine-treated lymphocytes. It was concluded that microtubules control the activity of AC by restricting the mobility of membrane receptors. Disruption of microtubules by drugs results in the removal of such restraints and an augmented chance of productive interactions between receptors and catalytic units of AC.

Fast axonal transport: effect of antimitotic drugs and inhibitors of energy metabolism on the rate and amount of transported protein in frog sciatic nerves

Mitosis inhibitors, drugs affecting the energy metabolism, heavy water, and ouabain were used to partially inhibit fast axonal transport in frog sciatic nerves. Effects on the rate and on the amount of pulse labeled protein could be separated. The pulse of labeled protein, released after a cold-block, rapidly reached a maximum height which indicated that the transport system was saturated in the nerve segment occupied by the pulse. Both the rate and the amount were reduced by the mitosis inhibitors colchicine, vinblastine, and griseofulvin. Colchicine had a differential effect and reduced the rate of material migrating in the advancing front of the pulse less than the rate of that moving in the peak. Preincubation at low temperature potentiated the effects of colchicine. Two inhibitors of energy metabolism, NaCN and IAA, reduced the amount of labeled material in the pulse. The slope of the pulse was markedly reduced and multiple peaks appeared. The distance covered by the migrating pulse was largely unaffected, but some retardation of late components might have occurred. In contrast, 2.4-DNP reduced the rate without any effects on the amount of migrating material. Heavy water uniformly reduced the rate of the migrating pulse, whereas the main effect of ouabain was a diminished amount and multiple peaks as with NaCN and IAA. All drugs were tested for their effects on the electrical activity of sciatic nerves. The compound action potential was not affected by the mitosis inhibitors and heavy water, but was depressed by the inhibitors of energy metabolism and abolished by ouabain. The results indicate that the effects of various transport inhibitory drugs can be differentiated if both the rate and the amount are considered.

Colchicine effects on lysosomal enzyme induction and intracellular degradation in the cultivated macrophage

The effects of colchicine on lysosomal fusion and lysosomal enzyme induction in the cultivated mouse peritoneal macrophage have been examined. Colchicine (10- minus 6 M), but not lumicolchicine, inhibited lysosomal enzyme induction by both phagocytic and pinocytic stimuli. In addition, the drug significantly retarded pinocytic uptake of [3-H] sucrose and transport of the amino acids [3-H] alpha aminoisobutyric acid and L-[3-H] leucine. In contrast, lumicolchicine had no effect on pinocytosis or amino acid transport. Thus, a role for intact microtubules in lysosomal enzyme induction, pinocytosis, and amino acid uptake in these cells is suggested. That colchicine inhibited lysosomal enzyme induction by phagocytic stimuli under conditions in which pinocytosis contributed little to the enzyme rise indicated that inhibition of pinocytosis was unlikely to account for colchicine effects on lysosomal enzyme induction. Effects of colchicine on degradation of phagocytized and pinocytized substrates were examined to determine if intact microtubules are required for fusion among lysosomes, pinosomes, and phagosomes. Colchicine did not alter the rate of intracellular digestion of radiolabeled bacteria by the cultivated macrophage. Similarly, it had no effect on enzymatic hydrolysis of intracellular [3-H] sucrose resulting from uptake of exogenous invertase. The finding that colchicine had no effect on the functional consequences of fusion of lysosomes with endosomes suggests that intact microtubules are not required for fusion among these constituents of the vacuolar apparatus.

Stability of neuronal microtubules to high pressure in vivo and in vitro

Neuronal microtubules in a variety of nerve cell types are unaffected by high hydrostatic pressures over a range of 1400-10,000 pounds/inch(2) and periods of 10-45 min. Similarly, purified tubulin polymerized to form microtubules in vitro were not depolymerized by the same range of pressures. The depolymerization of microtubules in several types of non-neuronal cells, which has been reported, may have been over-generalized with regard to the direct action of pressure on microtubule stability.

Mechanisms of lysosomal enzyme release from human leukocytes. II. Effects of cAMP and cGMP, autonomic agonists, and agents which affect microtubule function

Selective release of inflammatory materials from leukocyte lysosomes is reduced by compounds which increase cyclic 3',5'-adenosine monophosphate (cAMP) levels in suspensions of human leukocytes and is augmented by agents which increase cyclic 3',5'-guanosine monophosphate (cGMP) levels in these cell suspensions. Lysosomal enzymes are released in the absence of phagocytosis when cytochalasin B (5 mug/ml) converts polymorphonuclear leukocytes (PMN) to secretory cells: lysosomes merge directly with the plasma membrane upon encounter of PMN with zymosan, and cells selectively extrude substantial proportions of lysosomal, but not cytoplasmic enzymes. beta-Adrenergic stimulation of human leukocytes produced a dose-related reduction in beta-glucuronidase release (blocked by 10(-6) M propranolol) whereas alpha-adrenergic stimulation (phenylephrine plus propranolol) was ineffective. In contrast, the cholinergic agonist carbamylcholine chloride enhanced enzyme secretion, an effect blocked by 10(-6) M atropine. Incubation of cells with exogenous cAMP or with agents that increase endogenous cAMP levels (prostaglandin E1, histamine, isoproterenol, and cholera enterotoxin) reduced extrusion of lysosomal enzymes; in contrast, exogenous cGMP and carbamylcholine chloride (which increases endogenous cGMP levels), increased beta-glucuronidase release. Whereas colchicine (5 x 10(-4) M), a drug which impairs microtubule integrity, reduced selective enzyme release, deuterium oxide, which favors microtubule assembly, enhanced selective release of lyosomal enzymes. The data suggest that granule movement and acid hydrolase release from leukocyte lysosomes requires intact microtubules and may be modulated by adrenergic and cholinergic agents which appear to provoke changes in concentrations of cyclic nucleotides.

Mechanisms of lysosomal enzyme release from human leukocytes. I. Effect of cyclic nucleotides and colchicine

In order to study mechanisms underlying selective enzyme release from human leukocytes during phagocytosis, the effects were studied of compounds which affect microtubule integrity or the accumulation of cyclic nucleotides. Human leukocytes selectively extrude lysosomal enzymes (beta-glucuronidase) from viable cells during phagocytosis of zymosan or immune complexes, or upon encounter with immune complexes dispersed along a non-phagocytosable surface such as a millipore filter. In each circumstance, lysosomal enzyme release was reduced by previous treatment of cells with pharmacological doses of drugs which disrupt microtubules (e.g. 10(-3)-10(-5) M colchicine) or with agents which affect accumulation of adenosine 3'5'-monophosphate (cAMP) (e.g. 10(-3) M cyclic nucleotides and 2.8 x 10(-4)-2.8 x 10(-6) M prostaglandin E (PGE) and A (PGA) compounds). Preincubation of cells with 5 microg/ml cytochalasin B resulted in complete inhibition of zymosan ingestion, but not of adherence of zymosan particles to plasma membranes or selective enzyme release. In this system, in which enzyme release was independent of particle uptake, preincubation of cells with colchicine, vinblastine, dibutyryl cAMP, or PGE(1) also reduced extrusion of lysosomal enzymes. When cell suspensions were incubated with membrane-lytic crystals of monosodium urate (MSU), cytoplasmic as well as lysosomal enzymes were released with subsequent death of the cells. However, enzyme release followed phagocytosis of crystals (as measured by enhanced C-1 oxidation of glucose) and was due to "perforation from within" of the lysosomal membrane, rather than lysis by crystals of the plasma membrane. Enzyme release after MSU ingestion was also reduced when cells were treated with pharmacological doses of the test agents. When cells were killed by Triton X-100, acting on the plasma membrane, C-1 oxidation of glucose was abolished and enzyme release could not be inhibited pharmacologically. These observations suggest that lysosomal enzyme release from human phagocytes can be an active process which accompanies plasma membrane stimulation, is independent of cell death, and may be controlled by cyclic nucleotides and agents which affect microtubules.

Histamine release from human leukocytes: studies with deuterium oxide, colchicine, and cytochalasin B

Agents known to interact with either microtubules or microfilaments influenced the antigen-induced release of histamine from the leukocytes of allergic individuals. Deuterium oxide (D(2)O) which stabilizes microtubules and thereby favors their formation enhanced histamine release markedly. Concentrations as low as 5% increased antigen-induced release somewhat while concentrations as high as 75% had no effect on release in the absence of antigen. Enhancement occurred over a wide range of antigen concentrations and was also seen when release was initiated by antibody to IgE or IgG. When the release process was divided into two stages a D(2)O activity could be demonstrated only in the second stage. However, when D(2)O was present in the first stage together with agents which raise cyclic AMP levels and thereby inhibit release it partially reversed this inhibition. Colchicine, demecolcine, and vinblastine, compounds known to disaggregate microtubules, i.e., have an effect opposite to that of D(2)O, inhibited the release of histamine and counteracted the effects of D(2)O. The inhibitory action of colchicine was greater if cells were treated with colchicine before rather than after activation with antigen. Cytochalasin B, a compound which causes the disappearance of microfilaments, had variable effects on histamine release. The most frequently seen response was slight enhancement. Neither D(2)O nor cytochalasin B altered cyclic AMP levels in leukocytes. These observations support and strengthen the view that an intact and functioning microtubule system is directly important for the secretion of histamine from leukocytes and suggest that microfilaments might have multiple indirect effects.

Comparison of the microtubule proteins of neuroblastoma cells, brain, and Chlamydomonas flagella

Intact A microtubules isolated from outer doublet microtubules of Chlamydomonas flagella contain two separable proteins (tubulins) that differ in molecular weight and in amino-acid composition. The microtubule protein isolated from brain or neuroblastoma cells also has two electrophoretically distinct tubulins. Although the two tubulins of brain and neuroblastoma cells are electrophoretically similar to each other, only one of these tubulins migrates with the flagellar tubulins. This is the first evidence that (a) isolated, morphologically intact, single microtubules from flagella contain at least two different tubulins, and (b) at least one of these tubulins differs from tubulins that are isolated from other sources.