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PubMed1998

Alpha1A-adrenergic receptors mediate vasoconstriction of the isolated spiral modiolar artery in vitro.

Several lines of evidence suggest that cochlear blood flow is under the control of the sympathetic nervous system and that this control is mediated via alpha-adrenergic receptors. The goal of the present study was to determine whether alpha-adrenergic receptors mediate vasoconstriction of the spiral modiolar artery and, if so, to determine which subtype dominates this response. Vascular diameter was measured with video microscopy in the isolated superfused spiral modiolar artery in vitro. The diameter of the spiral modiolar artery under control conditions was 61 +/- 2 microm (n = 60). Spontaneous vasomotion was observed in most specimens. Addition of norepinephrine to the superfusate caused a phasic vasoconstriction and an increase in the amplitude of vasomotion. These effects were limited to the vicinity of arteriolar branch points of the spiral modiolar artery. Norepinephrine-induced vasoconstriction occurred with EC50 of (1.9 +/- 0.4) x 10(-5) M (n = 44) and the vascular diameter was maximally reduced by a factor of 0.87 +/- 0.01 (n = 29). Neither the phasic nature nor the EC50 of the norepinephrine-induced vasoconstrictions was altered in the presence of the beta2-adrenergic receptor antagonist 10(-5) M ICI118551 or the nitric oxide synthase inhibitor 10(-4) M NOARG. In contrast, the alpha2-adrenergic receptor antagonist 10(-7) M yohimbine and the alpha1-adrenergic receptor antagonist 10(-9) and 10(-8) M prazosin caused a significant shift in the dose-response curve. The affinity constants (K(DB)) for yohimbine and prazosin were (5+/-2) x 10(-8) M (n=4) and (2.0+/-0.7) x 10(-10) M (n=18), respectively. The alpha1A-adrenergic receptor antagonist 10(-8) M 5-methyl urapidil and the alpha1D-adrenergic receptors antagonist 5 x 10(-6) M BMY7378 caused a significant shift in the dose-response curve. The K(DB) values for 5-methyl urapidil and for BMY7378 were (2.7 +/- 0.7) x 10(-10) M (n = 8) and (4.4 +/- 2.7) x 10(-7) M (n = 8), respectively. Further, total RNA was isolated from microdissected spiral modiolar arteries and the presence of transcripts for alpha1-adrenergic receptor subtypes was determined by reverse transcription polymerase chain reaction (RT-PCR). Primers specific for gerbil alpha1-adrenergic receptor subtypes were developed using RNA from rat and gerbil brain. Analysis of RNA extracted from the spiral modiolar artery revealed RT-PCR products of the appropriate size for the alpha1A-adrenergic receptor, however, no evidence for the alpha1B- and alpha1D-adrenergic receptor was found. Further, analysis of RNA extracted from blood, which was a contaminant of the microdissected spiral modiolar arteries, revealed no RT-PCR products. Sequence analysis of the RT-PCR product of the alpha1A-adrenergic receptor from the spiral modiolar artery confirmed its identity. Identity between the 175 nt gerbil sequence fragment and the known rat, mouse and human alpha1A-adrenergic receptor sequences was 90.9, 92.0 and 85.2%, respectively. These observations demonstrate that the spiral modiolar artery contains alpha1A-adrenergic receptors which mediate vasoconstriction at branch points.

Adrenergic alpha-1 Receptor Antagonists↗
PubMed1997

Albumin microbubble adherence to human coronary endothelium: implications for assessment of endothelial function using myocardial contrast echocardiography.

OBJECTIVES: We hypothesized that sonicated 5% human albumin microbubbles (Albunex) adhere to disrupted vascular endothelium and that this interaction is a marker of endothelial integrity. This study sought to identify sites and determinants of Albunex-endothelial cell (EC) attachment. BACKGROUND: Under normal conditions, Albunex microbubbles used in myocardial contrast echocardiography (MCE) pass unimpeded through the coronary microcirculation. During pathophysiologic states associated with endothelial dysfunction, however, microbubbles linger in the myocardium despite normal flow. The sites and conditions regulating microbubble adhesion are unknown. METHODS: Coverslips with cultured human coronary artery ECs were mounted in a parallel plate perfusion system and perfused with a suspension of fluorescein-labeled Albunex in culture medium, followed by a bubble-free wash at a wall shear rate of 100 s-1. To create inflammatory ECs, phorbol myristate acetate was added 4.5 h before perfusion, and flow cytometry was used to confirm an inflammatory response. Perfusions were performed under normal and inflammatory conditions using surfaces of confluent and subconfluent ECs and isolated extracellular matrix. Bubble adherence was quantified in 20 random fields per cover-slip using epifluorescent video microscopy. RESULTS: No microbubbles adhered to normal confluent ECs, although small numbers adhered to inflamed ECs (0.03 +/- 0.01 bubbles/cell, p < 0.01 vs. normal cells). Fever microbubbles attached to normal versus inflamed matrix of both partially exposed (1,800 +/- 520 vs. 4,100 +/- 1,000 bubbles/mm2, p = 0.05) and completely denuded (2,700 +/- 1,300 vs. 7,200 +/- 1,100 bubbles/ mm2, p < 0.03) endothelium. CONCLUSIONS: Albunex microbubbles preferentially adhere to inflammatory endothelial extracellular matrix. These data suggest that MCE can be used to noninvasively study endothelial integrity and may have implications for the assessment of preclinical atherosclerotic heart disease.

Adhesiveness↗
PubMed2001

Physical and chemical stability of marine lipid-based liposomes under acid conditions.

Liposomes made from a marine lipid extract containing a high polyunsaturated fatty lipid ratio were submitted to large pH variations, ranging from 1 to 8. Shape transformations were followed by video microscopy using giant liposomes and micromanipulation experiments. Acidification induced a decrease of the vesicle size simultaneous to the appearance of invaginations. These pH-dependent structural rearrangements were interpreted in terms of osmotic shocks and chemical modifications of the membranes. Liposomes produced by direct filtration were studied using turbidity measurements and optical microscopy observations. A low pH led to an instantaneous vesicle aggregation and to complex supramolecular and/or morphological changes as a function of time. The subsequent buffer neutralization of the liposome suspensions induced a partial reversion of the aggregation phenomenon while the structural membrane rearrangements were persisting. Furthermore, weak chemical degradations (oxidation and hydrolysis) were evidenced when the vesicles were incubated at low pH up to a 24-h incubation time. Thus, although acidification revealed liposome size and shape changes, the bilayer structure was maintained indicating that marine lipid-based liposomes could be used as oral administration vectors.

Journal Article↗
PubMed2004

Prenatal growth of the interorbital septum in Macaca mulatta.

The interorbital septum is the portion of the anterior cranial base directly contiguous with the eyes. It is considered to be a primitive trait that has evolved independently in various primate groups as a result of ocular and olfactory convergence with concomitant encephalization. This process is hypothesized to have reduced the size of the lateral nasal capsule exposing the anterior cranial base to the ocular apparatus and thus creating an interorbital septum. The purpose of this study was to determine whether differential growth trajectories occur among the chondrocranial elements corresponding to this hypothesis. Macaca mulatta embryos from the Zingeser Collection were selected for this analysis since this primate shows a well-developed interorbital septum throughout ontogeny. Embryos between 40 and 90 days of gestation were selected from the collection and coronal sections including the eye, anterior cranial base and lateral nasal capsule were subjected to video microscopy and computerized reconstruction using SURFdriver Software. Tissue volumes were computed for these tissues while chondrocytic growth attributes were measured utilizing stereological techniques. Results showed a strong correlation between the volume of the lateral nasal capsule and anterior cranial base and these two structures showed a consistent correlation with an increasing eye volume. Chondrocytic volume density and average diameter were larger in the lateral nasal capsule while shape, numerical density and average volume did not differ between the two tissues. These data suggest if differential growth does account for a reduction of the nasal capsule compared to the central cranial base stem, it does not appear to result from differential tissue size change. However, certain cellular growth activities leading to premature chondrocytic hypertrophy may be involved.

Animals↗
PubMed1999

Effects of paclitaxel with or without cremophor EL on cellular clonogenic survival and apoptosis.

Paclitaxel is currently formulated in a vehicle of 50% ethanol and 50% polyethoxylated surfactant cremophor EL. Cremophor EL has been reported to reverse P-glycoprotein-mediated multidrug resistance (MDR) at doses which are clinically achievable. It has also been reported to have a cytotoxic effect per se. In this study we used two different methods to evaluate the survival of cells exposed to paclitaxel with or without cremophor EL and the vehicle alone. Two laryngeal SCC cell lines (UT-SCC-19A and UT-SCC-29) and two ovarian adenocarcinoma cell lines (UT-OC-3 and UT-OC-5) established in our laboratory were investigated. Northern hybridisation was used to study the mdr-1 mRNA expression of the cell lines. With sensitive Northern analyses, these four lines yielded mdr-1 mRNA signals of the expected 4.5 kb size and of variable intensity, generally at higher levels than those in the positive control cell line KB. The 96-well plate clonogenic assay was used to obtain the fraction survival data and apoptosis was recorded by time-lapse video microscopy. Both methods indicate that cremophor EL alone has no effect on cellular survival. Consequently, paclitaxel without cremophor EL is as active as paclitaxel with cremophor EL in vitro.

Adenocarcinoma↗
PubMed2001

Organized microtubule arrays in gamma-tubulin-depleted Drosophila spermatocytes.

To assess the role of gamma-tubulin in spindle assembly in vivo, we have followed meiosis progression by immunofluorescence and time-lapse video microscopy in gammaTub23C(PI) mutant spermatocytes. We have found that centrosomes associate with large numbers of astral microtubules even though gamma-tubulin is severely depleted; bipolar meiotic spindles are never assembled; and later in meiosis, the microtubules get organized into a conical structure that is never observed in wild-type cells. Several lines of evidence suggest that these cones may be related to wild-type central spindles. First, they are assembled midway through meiosis and elongate during anaphase. Second, they are constricted during late meiosis, giving rise to a pointed end similar to those that form in each half of the wild-type spindle midzone. Third, Klp3A and Polo, two markers of the wild-type central spindle are also found around the pointed end of the mutant cones. Finally, ectopic cytokinesis furrows are often formed at the distal end of the cone. Our results suggest that microtubule polymerization or stabilization from the centrosome may be possible in a gamma-tubulin-independent manner in Drosophila spermatocytes. However, gamma-tubulin seems to be essential for spindle assembly in these cells. Finally, our results show that at least part of the central spindle and constriction-ring assembly machinery can operate on microtubule bundles that are not organized as bipolar spindles.

Animals↗
PubMed2002

Chromosome segregation: pulling from the poles.

Dual wavelength video microscopy has been used to evaluate how chromatids move poleward upon chromosome separation at anaphase. The data reveal that poleward microtubule flux provides the dominant force for separating chromatids in Drosophila embryos during anaphase A.

Anaphase↗
PubMed2003

A WASp homolog powers actin polymerization-dependent motility of endosomes in vivo.

BACKGROUND: WASp/SCAR proteins activate the Arp2/3 complex to nucleate actin filament assembly and are thought to have important roles in endocytosis. WASp is required for efficient endocytosis of antigen receptors, N-WASp promotes actin polymerization-dependent movement of endomembrane vesicles, and Las17 (a yeast WASp homolog) is required for endocytic internalization. However, it is unknown whether movement of endosomes or other organelles requires activation of the Arp2/3 complex by members of the WASp/SCAR family. RESULTS: Fluorescence video microscopy of yeast cells expressing a GFP-tagged G protein-coupled receptor (Ste2-GFP) as an endocytic marker revealed that endosomes and the lysosome-like vacuole are highly motile. Endosome/vacuole motility required actin polymerization, as indicated by sensitivity to latrunculin A, whereas microtubules were uninvolved. Endosome/vacuole motility did not require actin cables or myosin V (a MYO2 gene product), which moves secretory vesicles and the Golgi apparatus and mediates vacuole segregation. However, endosome motility required Las17, a WASp homolog. In contrast to other processes involving Las17, endosome/vacuole motility required the WCA domain of Las17, which is necessary and sufficient to activate the Arp2/3 complex. CONCLUSIONS: Endosome/vacuole motility in vivo requires actin polymerization stimulated by the WASp homolog Las17. WASp/SCAR family members in mammalian cells may have similar functions. Defects in endosome/lysosome motility may contribute to deficits in lymphocyte or macrophage function observed in human patients lacking WASp or developmental defects in N-WASp-deficient mice.

Actins↗
PubMedDate not supplied

Targeting of different ethiodized oil-doxorubicin mixtures to hypovascular hepatic metastases with intraarterial and intraportal injections.

PURPOSE: The distribution of different ethiodized oil-doxorubicin mixtures within and around hypovascular liver metastases in athymic nude mice was compared following either intraarterial or intraportal injections. MATERIALS AND METHODS: Six different mixtures of doxorubicin and ethiodized oil in water-soluble contrast material, shaken for 5, 10, 15, and 30 minutes, respectively, were prepared and the size of the oil droplets in the mixtures evaluated. Intraarterial and intraportal injections of mixtures shaken for 10 and 15 minutes were performed in mice bearing hypovascular hepatic colorectal metastases. In vivo video microscopy was used to evaluate microvascular flow and the biodistribution and the size of the oil droplets within and around the tumors. RESULTS: Oil droplets smaller than 20 microns in diameter were taken up by tumor nodules. There was no significant difference in oil droplet accumulation within the tumor between intraarterial and intraportal injections. Oil droplets larger than 20 microns occluded small and medium portal branches. The optimum combination was 0.1 mL of ethiodized oil in 2 mL of diatrizoate sodium meglumine (Renografin-76) shaken for 15 minutes at 800 rpm, which formed droplets smaller than 20 microns (92%). CONCLUSION: Avascular regions of hepatic metastases may be embolized with ethiodized oil-anticancer drug mixtures containing oil droplets smaller than 20 microns. Since these droplets penetrate to the tumor interstitium with either intraarterial or intraportal injections, chemoembolization via the arterial route seems preferable for treatment of unresectable hypovascular hepatic metastases since it is easier to perform. The conclusions drawn from this study are limited to the animal model for experimental hypovascular hepatic metastases.

Animals↗
PubMed1998

Localization of ASH1 mRNA particles in living yeast.

ASH1 mRNA localizes to the bud tip in Saccharomyces cerevisiae to establish asymmetry of HO expression, important for mating type switching. To visualize real time localization of the mRNA in living yeast cells, green fluorescent protein (GFP) was fused to the RNA-binding protein MS2 to follow a reporter mRNA containing MS2-binding sites. Formation and localization of a GFP particle in the bud required ASH1 3'UTR (untranslated region) sequences. The SHE mutants disrupt RNA and particle localization and SHE 2 and 3 mutants inhibit particle formation as well. Both She3myc and She1myc colocalized with the particle. Video microscopy demonstrated that She1p/Myo4p moved particles to the bud tip at 200-440 nm/sec. Therefore, the ASH1 3'UTR-dependent particle serves as a marker for RNA transport and localization.

3' Untranslated Regions↗
PubMed1997

Functional analysis by imaging of melanophore pigment dispersion of chimeric receptors constructed by recombinant polymerase chain reaction.

Analysis of functional aspects of the molecular structure of proteins often requires a means to selectively alter structure and subsequently analyze function. We have adapted a method of overlap extension polymerase chain reaction (PCR) to generate multiple domain replacements in G-protein coupled receptors. The examples described herein are beta 2-adrenergic receptors whose G-protein coupling domains have been replaced by homologous domains of olfactory receptors, but the procedure has also been used to produce constructs with mutations, deletions, and fusions of two complete open reading frames. The chimeric olfactory-adrenergic receptors were assayed by functional expression in clonal lines of Xenopus melanophores. The ability of G-protein coupled second messenger pathways to cause translocation of pigment organelles within melanophores allows the use of video microscopy to assay the function of the chimeric receptors. Digital automation of microscope stage, camera, and image processing allows multiple parallel experiments to be performed. Melanophores allow responses mediated by the Gs, Gq and Gi pathways to be assayed with equal efficiency and the specificity of the coupling between chimera (or receptor) and G-protein subtypes can be rapidly determined.

Animals↗
PubMed2003

The heart of Daphnia magna: effects of four cardioactive drugs.

We used Daphnia magna bioassays to determine the LC(50) and the effects on the heart of the cardioactive drugs ouabain, verapamil, metaproterenol and metoprolol. Distinctions were made between the pharmacological and toxicological effects of these drugs and the adequacy of physicochemical characteristics of its habitat (reconstituted water). Video microscopy and digital image processing were used to study the pharmacological effects on the heart. D. magna exhibited the expected sensitivity to the reference toxicant sodium dodecyl sulfate with a LC(50) of 15.6+/-4.5 mg/l. All drugs were toxic with 48 h-LC(50) of 2.03 mg/l ouabain, 7.04 mg/l verapamil, 32.45 mg/l metaproterenol and 76.21 mg/l metoprolol. Ouabain was the most toxic and caused a positive concentration-dependent inotropic effect. Verapamil caused positive chronotropic and inotropic effects, while metaproterenol showed positive concentration-dependent chronotropic effects at high concentrations (10(-3) and 10(-4) M). Metoprolol induced a positive chronotropic effect at low concentrations (10(-8), 10(-7), 10(-6) M) and a negative chronotropic effect at high concentration (10(-4) M). Ouabain, metaproterenol and metoprolol in D. magna caused similar effects to those produced in mammals. In contrast, verapamil caused opposite effects. The results suggest the presence of Na(+), K(+)-ATPase receptors to verapamil and of non-specific adrenergic receptors in heart of D. magna.

Animals↗
PubMed2002

In vivo imaging reveals different cellular functions for FGF and Dpp signaling in tracheal branching morphogenesis.

In the developing tracheal system of Drosophila melanogaster, six major branches arise by guided cell migration from a sac-like structure. The chemoattractant Branchless/FGF (Bnl) appears to guide cell migration and is essential for the formation of all tracheal branches, while Decapentaplegic (Dpp) signaling is strictly required for the formation of a subset of branches, the dorsal and ventral branches. Using in vivo confocal video microscopy, we find that the two signaling systems affect different cellular functions required for branching morphogenesis. Bnl/FGF signaling affects the formation of dynamic filopodia, possibly controlling cytoskeletal activity and motility as such, and Dpp controls cellular functions allowing branch morphogenesis and outgrowth.

Animals↗
PubMedDate not supplied

Distribution of GABA(C)-like responses among acutely dissociated rat retinal neurons.

GABAergic responses of acutely dissociated rat retinal neurons, including both bipolar cells (BCs) and other, morphologically round cells (RCs), were assayed with the fluorescent (FL), voltage-sensitive probe oxonol DiBaC4(5). Using intensified video microscopy and simultaneous recording, GABA responses were identified in one-third of cells in a typical microscope field; of these 85% hyperpolarized (0.05-0.3 log unit FL decreases) while the remainder depolarized (0.05-0.2 log unit FL increases). GABA-sensitive cells were also TACA-sensitive (trans-4-Aminocrotonic acid), and these ligands appeared interchangeable in ability to evoke responses. In RCs, an asymmetric co-responsive pattern was observed between GABA- and muscimol-evoked events. Muscimol-sensitive RCs responded well to GABA, but not all GABA-sensitive RCs responded to muscimol. In GABA-sensitive BCs, muscimol responses were typically weak or absent. Few BCs or RCs responded to CACA (cis-4-Aminocrotonic acid). Bicuculline-resistant GABA responses occurred in approximately 80% of GABA-responsive RCs and BCs. Both bicuculline-sensitive (GABA(A)-like) and bicuculline-insensitive (GABAc-like) responses were resistant to picrotoxin. Although a small minority of GABA-sensitive cells hyperpolarized in response to R(+)baclofen, bicuculline-insensitive responses were not antagonized by 2-hydroxysaclofen, and were abolished in low [Cl-]o. Results suggested (1) that bicuculline-insensitive, Cl(-)-dependent, GABAc-like responses were broadly distributed and predominant among dissociated rat retinal neurons; (2) that muscimol was a particularly weak agonist for rat retinal BCs; and (3) that oxonol was a sensitive probe for retinal GABA responses.

Animals↗
PubMed1994

Spontaneous injection in microcolumn separations.

The phenomenon of spontaneous (ubiquitous) injection in microcolumn separations has been characterized to improve quantitative precision for ultramicrosampling and to enhance separation efficiency. By combining fluorescence imaging, video microscopy, and measurements from capillary electrophoresis, we demonstrate that spontaneous injection is caused primarily by an interfacial pressure difference formed at the inlet of the capillary. This complex injection mechanism has been modeled with some simple assumptions based on fluid dynamics. In particular, studies showed that extraneous injection is reduced up to 12-fold by etching the capillary inlet or by using a thin-walled capillary. Variations by a factor of 2 in the injection length can result from delays between sample introduction and reinsertion into the inlet vial if the timing is not controlled precisely. Evidence is presented that evaporation of buffer from the inlet can reduce the injection length by more than 1 order of magnitude.

Image Processing, Computer-Assisted↗
PubMed1995

Dynamics of DNA during pulsed field electrophoresis in entangled and dilute polymer solutions.

Using fluorescence video microscopy, DNA electrophoretic behavior under field inversion conditions has been investigated in hydroxyethyl cellulose (HEC) solutions both above and below its entanglement limit. DNA conformational fluctuation periods are found to be strongly influenced by the frequency of the applied electric field. DNA maximum extension is found to be dependent on both the frequency and the strength of the applied field. It is proposed that both above and below the HEC entanglement limit, field inversion serves to keep the average DNA conformation in a size-dependent regime intermediate between full extension and random coil. In this time-averaged geometry, efficient long-chain DNA electrophoretic separation is enabled.

DNA, Fungal↗
PubMed1995

Regulation of microtubule dynamic instability by tubulin-GDP.

The regulation of the spontaneous transitions between growth and shortening of microtubules is central to the biological function of dynamic instability. Here we examine the effects of controlled amounts of tubulin-GDP (Tu-GDP) on the dynamic properties of microtubules in vitro. The transphosphorylation equilibrium between GTP, GDP, UTP, and UDP in the presence of nucleoside-5'-diphosphate kinase (NDPK) was used to fix the ratio chi D = [Tu-GDP]/([Tu-GTP]) + [Tu-GDP]) in solution. Lower levels of Tu-GDP (chi D < 0.6) produce only a small increase in the apparent critical concentration, Cc'. However, at chi D > 0.6 a dramatic increase in Cc is observed. At steady state of assembly, low levels of Tu-GDP (chi D < 0.5) cause a significant reduction of the dynamic length redistribution of the microtubule population. The principal observable effect of Tu-GDP on the empirical parameters of microtubule dynamic instability is to decrease the duration of individual phases of microtubule growth and shortening, with relatively little effect on the intrinsic rates of growth and shortening. Observations in dark-field video microscopy reveal that the irregularities in the rates of growth (and shortening) are increased in the presence of Tu-GDP. At elevated levels of Tu-GDP, pauses occur frequently during the growth phase, microtubule dynamics cease to conform to a clear two-phase process, and the extents of growth and shortening excursions are strongly attenuated. The experimental results are well reproduced by computer simulation, using mechanisms defined in the lateral cap model for dynamic instability [Martin, S. R., Schilstra, M. J., & Bayley, P. M. (1993) Biophys. J. 65, 578-596], which includes the binding of Tu-GDP to the microtubule end in competition with Tu-GTP. In the presence of Tu-GDP, the growing-state lifetime is significantly attenuated, and the microtubule length versus time excursions simulated by the model show irregularities and complex multistate behavior, including pauses, as observed experimentally. These results suggest that Tu-GDP can modulate microtubule dynamics significantly under conditions where little bulk microtubule disassembly is induced. Tu-GDP therefore appears to exemplify the action of a relatively simple factor with the potential capability for regulation of microtubule dynamics in a cellular environment.

Computer Simulation↗
PubMed1993

Kinetic stabilization of microtubule dynamic instability in vitro by vinblastine.

The antiproliferative action of vinblastine at low concentrations appears to result from modulation of the polymerization dynamics of spindle microtubules rather than from depolarization of the microtubules [Jordan, M. A., Thrower, D., & Wilson, L. (1991) Cancer Res. 51, 2212-2222; (1992) J. Cell. Sci. 102, 401-416]. In the present study, we used differential interference contrast video microscopy to analyze the effects of vinblastine on the growing and shortening dynamics (dynamic instability) of individual bovine brain microtubules in vitro. With microtubules which were either depleted of microtubule-associated proteins (MAPs) or rich in MAPs, low concentrations of vinblastine (0.2 microM-1 microM) suppressed the growing and shortening rates and increased the percentage of time that the microtubules spent a state of attenuated activity, neither growing nor shortening detectably. Vinblastine also suppressed the duration of microtubule growing and shortening, and increased the duration of the attenuated state, during which the microtubules neither grew nor shortened detectably. Consistent with previous data obtained using radiolabeled nucleotide exchange in microtubule suspensions [Jordan, M. A., & Wilson, L. (1990) Biochemistry 29, 2730-2739], vinblastine suppressed growing and shortening dynamics at the kinetically more rapid plus ends. The results suggest that vinblastine kinetically stabilizes microtubule ends by modulating the gain and loss of the stabilizing GTP or GDP-Pi "cap", which is believed to be responsible for the transitions between the growing and shortening phases. The data support the hypothesis that (1) low concentrations of vinblastine inhibit mitosis by kinetically stabilizing the polymerization dynamics of spindle microtubules and that (2) the dynamics of spindle microtubules are critical for the proper progression of mitosis.

Animals↗