X-ray microscopy and imaging of Escherichia coli, LPS and DNA

Ultrastructural examination by transmission and scanning electron microscopy involves a series of specialized preparation steps which may introduce artefacts in the micrographs. X-ray microscopy can take instant images of specimens but is mostly restricted to a few synchrotron X-ray sources. We have utilized a bench-top nanosecond laser-plasma to produce a single-shot source of nanosecond X-rays tuned for maximum contrast with carbon-rich material. To examine the ultrastructure by absorption profiles, we utilized a laser-produced plasma generated by a single-shot laser (1.06 microns wavelength, 5 x 10(12) W cm-2 intensity) focused on to a silicon target as an X-ray source for high-resolution X-ray microscopy. This approach eliminates the specimen preparation steps. Whole hydrated cells of Escherichia coli and purified preparations of lipopolysaccharide (LPS) and chromosomal DNA (cDNA) were streaked onto poly(methyl methacrylate) (PMMA)-coated grids (resist). This resist was exposed to X-rays under vacuum at a distance of 2.5 cm from the target disc. The silicon plasma produced by a 10-ns burst of laser energy (at 20J) radiates strong emission lines in the region of 300 eV. The X-rays penetrate the sample and their absorption profile is transferred on to the resist where PMMA acts as a negative to generate an image. By atomic force microscopy imaging of this photoresist we have visualized layers around cells of E.coli, darker areas inside the cell probably corresponding to cDNA, and preliminary images of LPS and DNA molecules. This technique has resolution at the 100 A level, produces images similar to the space-filling models of macromolecules and may be of great value in the study of the ultrastructure of hydrated live biological specimens.

Participatory research methods: people with learning difficulties

The use of participatory research methods as a means of empowering disadvantaged and oppressed groups or individuals has attracted increasing interest in recent years. This article critically examines the use of such methods to empower people with learning difficulties as co-researchers. Emancipatory research would, by definition, be led and processed by people with learning difficulties. For the time being, however, the possibility of engaging people with learning difficulties in truly emancipatory nursing research is regarded as highly problematic, since it assumes empowerment as a precondition. As a step towards emancipatory research, participatory research represents a radical shift in the research process. It may potentially strengthen the voice of people with learning difficulties and enable them to express their views on nursing. The author proposes a methodology which addresses a number of critical issues facing the nurse researcher. It is a step towards developing more liberating and emancipatory methodologies.

Respiratory infection in lipid-fed rabbits enhances sudanophilia and the expression of VCAM-1

The pathogenesis of atherosclerosis has been related to infection of the arterial wall, but it is not clear whether this occurs before or after the development of lipid-containing lesions. Respiratory bacterial infection increases the expression of vascular cell adhesion molecule-1 (VCAM-1). We therefore examined whether a similar infection would enhance atherosclerosis in New Zealand White rabbits fed chow supplemented by 15% (w/w) egg yolk for 50 days. Rabbits with naturally acquired respiratory infection by Pasteurella multocida, pathogen-free (SPF) animals infected by P. multocida in the laboratory, and age-matched SPF rabbits maintained in a disease-free environment were used. Endothelial cells expressing VCAM-1 in the aorta between intercostal arteries 3 and 5 were identified using anti-VCAM-1 (Rb1/9) and an alkaline-phosphatase-linked secondary antibody and quantified in Häutchen preparations. The remainder of the aorta was stained with Sudan IV to show lipid deposition. The expression of VCAM-1 (mean +/- SEM per 10,000 cells) was 22 +/- 8 (n = 5) in the lipid-fed SPF rabbits, significantly different from that in the lipid-fed rabbits with naturally occurring infection (190 +/- 51 (n = 5)) or from rabbits infected in the laboratory (106 +/- 25 (n = 5)). The extent of Sudanophilia was significantly greater in the naturally infected rabbits (8.3 +/- 1.2%) or infected SPF rabbits (10.3 +/- 1.8%) than in the SPF rabbits (2.7 +/- 0.8%; P < 0.05). Antibiotic treatment in naturally infected rabbits reduced the number of cells expressing VCAM-1 and the extent of the Sudanophilia to baseline levels. Thus, Sudanophilia is enhanced by bacterial infection in rabbits fed egg yolk and is associated with a significant increase in VCAM-1.

Genome and MIC stability in Mycobacterium tuberculosis and indications for continuation of use of isoniazid in multidrug-resistant tuberculosis

Mycobacterium tuberculosis strains resistant to two or more of the first line antituberculosis drugs (MDR) are a serious threat to successful tuberculosis control programmes. For this retrospective study, 85 follow-up drug resistant isolates from 23 patients residing in a community with a high incidence of tuberculosis were collected and the level of in-vitro resistance to antibiotics determined quantitatively. PCR-SSCP and sequencing techniques were used to screen for gene mutations associated with resistance in 31 follow-up samples from a smaller group of eight patients. DNA fingerprint analysis was done on sequential isolates to confirm identity. Although treatment had a profound effect on changes in drug resistance patterns, the MIC for a particular agent remained constant in follow-up isolates. DNA fingerprinting and mutational analysis (14 different loci) showed that the genome of MDR strains of M. tuberculosis is relatively stable during the course of therapy. The rpoB gene was the most frequently mutated structural gene involved in drug resistance and a novel C to T mutation upstream of open reading frame (ORF)1 of the inhA operon was detected. No evidence was found of the presence of strain W (New York) in this group of MDR strains. The results stress the importance of confirming individuality of strains for the accurate calculation of frequencies of particular mutations associated with drug resistance, particularly in a high incidence area. Approximately one-half (47.8%) of the patients had isolates resistant to concentrations just above the critical concentration for isoniazid (MICs of 0.2-5 mg/L). Therefore, these patients and their contacts who develop primary drug-resistant tuberculosis may respond to higher dosages of treatment which could have a considerable impact on the cost and the ease of management of resistant tuberculosis.

Functional diversity and interactions between the repeat domains of rat intestinal lactase

Lactase-phlorizin hydrolase (LPH), a major digestive enzyme in the small intestine of newborns, is synthesized as a high-molecular-mass precursor comprising four tandemly repeated domains. Proteolytic cleavage of the precursor liberates the pro segment (LPHalpha) corresponding to domains I and II and devoid of known enzymic function. The mature enzyme (LPHbeta) comprises domains III and IV and is anchored in the brush border membrane via a C-terminal hydrophobic segment. To analyse the roles of the different domains of LPHalpha and LPHbeta, and the interactions between them, we have engineered a series of modified derivatives of the rat LPH precursor. These were expressed in cultured cells under the control of a cytomegalovirus promoter. The results show that recombinant LPHbeta harbouring both domains III and IV produces lactase activity. Neither domain III nor IV is alone sufficient to generate active enzyme, although the corresponding proteins are transport-competent. Tandem duplication of domains III or IV did not restore lactase activity, demonstrating the separate roles of both domains within LPHbeta. Further, the development of lactase activity did not require LPHalpha; however, LPHalpha potentiated the production of active LPHbeta but the individual LPHalpha subdomains I and II were unable to do so. Lactase activity and targeting required the C-terminal transmembrane anchor of LPH; this requirement was terminal transmembrane anchor or LPH; this requirement was not satisfied by the signal/anchor region of another digestive enzyme: sucrase-isomaltase. On the basis of this study we suggest that multiple levels of intramolecular interactions occur within the LPH precursor to produce the mature enzyme, and that the repeat domains of the precursor have distinct and specific functions in protein processing, substrate recognition and catalysis. We propose a functional model of LPHbeta in which substrate is channelled from an entry point located within domain II to the active site located in domain IV.

An evaluation of nebulized prostacyclin in patients with primary and secondary pulmonary hypertension

AIMS

To investigate the response to inhaled prostacyclin in patients with primary and secondary pulmonary hypertension and to compare its effects to those of intravenous prostacyclin and inhaled nitric oxide.

METHODS AND RESULTS

Twelve patients with pulmonary hypertension (seven primary and five secondary) were studied. All patients had a pulmonary artery balloon flotation catheter inserted into the proximal pulmonary artery and radial arterial line. Prostacyclin was nebulized with 81.min-1 of oxygen and administered in doses increasing from 15 to 50 ng.kg-1.min-1 via a facemask. Eight of these patients also received intravenous prostacyclin in doses of 1 to 5 ng.kg-1.min-1 and nitric oxide in doses of 10 to 100 ppm via a facemask. Haemodynamic measurements were taken during each treatment. In the 12 patients, nebulized prostacyclin produced a significant reduction in mean pulmonary artery pressure from 56 +/- 5 to 45 +/- 4 mmHg (P = 0.0001). The pulmonary vascular resistance decreased by 38% from 964 +/- 169 to 595 +/- 116 dyne.s-1.cm-5 (P = 0.0001). Direct comparison with inhaled nitric oxide and intravenous prostacyclin in eight patients demonstrated that nebulized prostacyclin produced a greater fall in mean pulmonary artery pressure than the other two agents without any significant effect on systemic arterial pressure.

CONCLUSION

Nebulized prostacyclin appears to be more effective at reducing pulmonary artery pressure in patients with pulmonary hypertension when compared to intravenous prostacyclin and inhaled nitric oxide. This could have important clinical implications for the management of patients with pulmonary hypertensions.

Addressing barriers: disabled rights and the implications for nursing of the social construct of disability

Drawing upon the writings of disabled people, this paper explores some of the issues which nurses working with disabled people are trying to address, in particular the barriers model of disability. Traditionally disability has been regarded as a personal tragedy afflicting the individual, hence the response to disability has been via the charity, health and welfare systems. Disabled people over the past two decades have substantially challenged this view of disability and the responses it prompts, arguing that disability is created by social barriers and barriers in the built environment. This requires a different response. Nurses working with disabled people, such as learning disability nurses, have struggled to develop more appropriate responses to disability, for example by developing working alliances with people with learning difficulties in order to both promote health and address disabling barriers. The issues these nurses face and some of the lessons disabled people have taught them are relevant to the nursing profession's wider struggle to shed its medical and dependency image.

Managing for quality in a nursing home: a resident-directed approach

As the population ages, the need for nursing care services will increase. Consumer focus on quality of life as well as reduction of expenditures poses a major challenge to the traditional nursing home, which often reinforces dependent resident behavior. The authors propose various strategies for improving life satisfaction and functional status of residents as well as efficiency and productivity of staff.

Ultrafast semiconductor laser-diode-seeded Cr:LiSAF regenerative amplifier system

An ultrafast, hybrid mode-locked semiconductor laser-diode system has been used to seed a flash-lamp-pumped Cr:LiSAF regenerative amplifier system, producing subpicosecond pulses with millijoule output pulse energy. This system has the potential to eliminate argon-ion-pumped-based, ultrafast laser systems.

Receptor and G betagamma isoform-specific interactions with G protein-coupled receptor kinases

The G protein-coupled receptor (GPCR) kinases (GRKs) phosphorylate and desensitize agonist-occupied GPCRs. GRK2-mediated receptor phosphorylation is preceded by the agonist-dependent membrane association of this enzyme. Previous in vitro studies with purified proteins have suggested that this translocation may be mediated by the recruitment of GRK2 to the plasma membrane by its interaction with the free betagamma subunits of heterotrimeric G proteins (G betagamma). Here we demonstrate that this mechanism operates in intact cells and that specificity is imparted by the selective interaction of discrete pools of G betagamma with receptors and GRKs. Treatment of Cos-7 cells transiently overexpressing GRK2 with a beta-receptor agonist promotes a 3-fold increase in plasma membrane-associated GRK2. This translocation of GRK2 is inhibited by the carboxyl terminus of GRK2, a known G betagamma sequestrant. Furthermore, in cells overexpressing both GRK2 and G beta1 gamma2, activation of lysophosphatidic acid receptors leads to the rapid and transient formation of a GRK/G betagamma complex. That G betagamma specificity exists at the level of the GPCR and the GRK is indicated by the observation that a GRK2/G betagamma complex is formed after agonist occupancy of the lysophosphatidic acid and beta-adrenergic but not thrombin receptors. In contrast to GRK2, GRK3 forms a G betagamma complex after stimulation of all three GPCRs. This G betagamma binding specificity of the GRKs is also reflected at the level of the purified proteins. Thus the GRK2 carboxyl terminus binds G beta1 and G beta2 but not G beta3, while the GRK3 fusion protein binds all three G beta isoforms. This study provides a direct demonstration of a role for G betagamma in mediating the agonist-stimulated translocation of GRK2 and GRK3 in an intact cellular system and demonstrates isoform specificity in the interaction of these components.

Increased expression of vascular cell adhesion molecule-1 by the aortic endothelium of rabbits with Pasteurella multocida pneumonia

Vascular cell adhesion molecule-1 (VCAM-1) is expressed by endothelial cells in a variety of inflammatory conditions in experimental animals and humans. It is increased in rabbit endothelium after the intravenous administration of endotoxin, after cholesterol feeding, in regeneration after injury, and in alloxan-induced diabetes mellitus. The effect of a respiratory tract infection with Pasteurella multocida, a common laboratory pathogen in rabbits, on VCAM-1 expression by aortic endothelial cells and on the endothelial ultrastructure was examined in specific-pathogen-free (SPF) New Zealand White rabbits infected by the instillation of a suspension of live organisms into the nose and in conventionally raised rabbits with naturally acquired P. multocida infection. Age-matched SPF rabbits maintained in a disease-free environment were controls. Rabbits were euthanized 50 days after infection, the aorta was excised, and the endothelial cells expressing VCAM-1 were identified by immunohistochemistry. Perfusion-fixed aortas from infected and SPF rabbits were prepared for examination by electron microscopy. All infected animals had pneumonitis and leukocytosis. In SPF rabbits the total leukocyte count was highest at postinfection day 25. There was a significant (P < 0.05) increase in the number of VCAM-1-positive aortic endothelial cells in infected SPF rabbits (34 +/- 4/10(4) endothelial cells; n = 5) and rabbits with naturally acquired infection (57 +/- 14/10(4) endothelial cells; n = 5) compared with control animals (12 +/- 3 per 10(4) endothelial cells; n = 4). The endothelium of infected rabbits had morphologic alterations consistent with injury. Thus infection at remote sites can activate arterial endothelium and induce the expression of VCAM-1.

Hazardous materials exposure information service: development, analysis, and medical implications

The Hazardous Materials Exposure Information Service (HMEIS) was established at the Washington Poison Center (WPC) to rapidly provide information to medical professionals who treat victims of hazardous-materials exposure. Incident description and exposure information is collected from on-site hazardous-materials teams and immediately analyzed by WPC medical toxicologists. Diagnostic and treatment recommendations are provided to prehospital personnel and receiving physicians. Over the first 22 months of operation, 50 calls were received that met HMEIS criteria. Of the 466 individuals exposed, 256 (55%) were transported to a medical facility for treatment. When the WPC was contacted before the decision to transport a patient to a medical facility, 28 of 185 exposure victims (15%) were transported, compared with a transport rate of 81% of exposure victims (66% change; 95% confidence interval [CI], 60% to 72%) in all other concurrent incidents and a historical transport rate of 63% (25% change; 95% CI, 14% to 36%) before the establishment of the HMEIS. These findings, although preliminary and subject to potential confounding, suggest that the HMEIS reduces health care costs through more efficient use of medical resources.

Molecular cloning and functional reconstitution of a urate transporter/channel

Maintenance of urate homeostasis requires urate efflux from urate-producing cells with subsequent renal and gastrointestinal excretion. The molecular basis for urate transport, however, has not been identified. A novel full-length cDNA encoding a 322-amino acid protein, designated UAT (urate transporter), has been cloned from a rat renal cDNA library by antibody screening. UAT mRNA transcripts that approximate 1.55 kilobases are present, but differentially expressed in various rat tissues. Recombinant UAT protein that was expressed from the cloned cDNA in Escherichia coli and purified via immobilized metal affinity chromatography has been functionally reconstituted as a highly selective urate transporter/channel in planar lipid bilayers. The IgG fraction of the polyclonal antibody that was used to select the UAT clone from the cDNA library, but not nonimmune IgG, blocked urate channel activity. Based on the wide tissue distribution of the mRNA for UAT we propose that UAT provides the molecular basis for urate flux across cell membranes, allowing urate that is formed during purine metabolism to efflux from cells and serving as an electrogenic transporter that plays an important role in renal and gastrointestinal urate excretion.

Ecotoxicity monitoring--use of Vibrio fischeri

The proliferation of chemical substances having the potential to pollute any environmental medium (air, land, water), or humans via occupational exposure, la considerable. Whilst chemical analytical techniques exist for the measurement of some of these chemicals, many of the methods involve costly techniques of considerable sophistication-quantification may be even more difficult. In less developed countries where sophisticated techniques may not be available or supplies of reagents, compressed gases or even electricity cannot be guaranteed, generic techniques have a great deal to offer. An emission of a chemical will cause adverse effects to organisms and hence there is an enormous advantage in measuring such effects on biological systems. One such technique is the reduction of light output In the presence of a toxicant to the marine bacteria Vibrio fischeri (formerly known as Photobacterium phosphoreum NRRL B-11177). A dark variant M-169 can also be used to obtain mutagenicity data. A chronic test whose results compare well with Ceriodaphnia dubia, has also been developed. The development of the principles of environmental toxicology assessment is reviewed together with the concept of toxic insult as a pragmatic tool in environmental risk assessment.

Complete amino acid sequences of two trypsin inhibitors from buckwheat seed

The major trypsin isoinhibitors from seed extracts of buckwheat (Fagopyrum esculentum Mönch) were purified by affinity chromatography, anion exchange chromatography, anion exchange HPLC and reversed-phase HPLC, and the complete amino acid sequences of two isoinhibitors, BTI-1 and BTI-2, were established by automated Edman degradation. Each isoinhibitor consists of a single polypeptide chain of 69 amino acids, including two Cys residues. The N-terminal sequence of a third isoform, BTI-3, was also determined. The buckwheat trypsin isoinhibitors exhibit clear sequence similarities with the potato chymotrypsin inhibitor I family of serine proteinase inhibitors.

An increased uptake of prothrombin, antithrombin, and fibrinogen by the rabbit balloon-deendothelialized aorta surface in vivo is maintained until reendothelialization is complete

The ability of the rabbit aorta intima-media (IM) layer to adsorb certain plasma proteins was measured for up to 20 months after a deendothelializing injury in vivo. Purified radioiodinated rabbit fibrinogen, antithrombin, or prothrombin was injected intravenously into either uninjured or sham-injured rabbits (controls) or rabbits at various times (5 minutes to 20 months) after a balloon-catheter injury to the aorta. After a 10-minute circulation time, a blood sample was taken, and the rabbit was exsanguinated rapidly (via a carotid cannula) and the aorta excised. Uptake of each radiolabeled protein was measured as bound radioactivity per square centimeter of platelet- or endothelium-free aorta IM and was compared with the radioactivity (ergo concentration) in blood at exsanguination. Fibrinogen adsorption by the IM was maximal at 5 minutes after injury (10.9 +/- 2.3 pmol/cm2 IM) and declined slowly to 4 to 6 pmol/cm2 at 12 months (controls: 0.8 +/- 0.1 pmol/cm2). Uptake of prothrombin (3.7 +/- 0.5 pmol/cm2 at 5 minutes) decreased to approximately 2 pmol/cm2 at 12 months (controls: 0.3 pmol/cm2). Antithrombin adsorption by the IM (3.3 +/- 0.4 pmol/cm2 at 5 minutes) paralleled that of prothrombin over 12 months (controls: 0.3 to 0.4 pmol/cm2), the molar ratio ranging from 0.8 to 1.2. At 20 months, the ballooned aorta had a significantly thickened intima and was approximately 90% reendothelialized. Injection of horseradish peroxidase (HRP) into rabbits at 1 or 12 months after balloon injury showed clearly that HRP activity was present throughout the entire depth of the deendothelialized, but not the reendothelialized, thickened intima. These results may indicate that an elevated turnover of hemostatic proteins continues within the deendothelialized intima after injury, conceivably until reendothelialization is complete.

Genotyping of Mycobacterium tuberculosis with additional markers enhances accuracy in epidemiological studies

Two highly polymorphic Mycobacterium tuberculosis genomic domains, characterized by hybridization to the oligonucleotide (GTG)5, were identified as potential DNA fingerprinting probes. These domains were cloned [pMTB484(1) and pMTB484(2K4), respectively] and shown to be useful for genotype analysis by Southern blotting. These probes were used to genotype geographically linked strains of M. tuberculosis previously shown to have identical IS6110 fingerprints. Subsequent DNA fingerprints generated with MTB484(1) and MTB484(2K4) showed a high degree of polymorphism, allowing subclassification of IS6110-defined clusters into composites of smaller clusters and unique strains. Correlation of the molecular data with patient interviews and clinical records confirmed the sensitivity of these probes, as contacts were established only within subclusters. These findings demonstrate the requirement for multiple probes to accurately classify M. tuberculosis strains, even those with high copy numbers of IS6110. The enhanced accuracy of strain typing should, in turn, further our understanding of the epidemiology of tuberculosis.

Bacterial meningitis

Over the last 10 years, our understanding of bacterial meningitis has improved considerably and new methods of treatment and prevention have been introduced. This review summarizes these advances and discusses more recent developments which will affect the management of bacterial meningitis in the near future.

alpha-Amylase inhibitors from wheat: amino acid sequences and patterns of inhibition of insect and human alpha-amylases

Four alpha-amylase inhibitors, WRP24, WRP25, WRP26, and WRP27, were purified from wheat flour by preparative, reversed-phase high performance liquid chromatography. All have polypeptide molecular masses of about 14 kDa and are members of the cereal superfamily of protease and alpha-amylase inhibitors. Sedimentation velocity analysis indicated that WRP25 and WRP27 are monomeric proteins, whereas WRP24 is a dimer. WRP24 is identical in N-terminal amino acid sequence to the well characterized 0.19 dimeric inhibitor from wheat kernels. WRP25 and WRP26 differ in sequence from each other at only three positions and represent previously unseparated forms of the 0.28 wheat inhibitor. WRP27 is a previously uncharacterized inhibitor and is more similar in sequence to the 0.28 inhibitor than to the 0.19 inhibitor. WRP25 and WRP26 inhibited alpha-amylases from the rice weevil, red flour beetle, and the yellow meal worm, but did not inhibit human salivary alpha-amylase. WRP24 inhibited the human as well as the insect alpha-amylases, but inhibited one of the two rice weevil alpha-amylases much more strongly than the other. WRP27 was notable in that, of the enzymes tested, it strongly inhibited only the rice weevil alpha-amylases. We observed that the growth rate of red flour beetle larvae was slowed when purified WRP24 was included in the diet at a level of 10%. Addition of WRP24 to corn starch resulted in greater weight loss of red flour beetle adults than occurred on control diets. Our results support the hypothesis that these alpha-amylase inhibitors provide wheat seeds with a selective evolutionary advantage since the inhibitors can slow the growth of insect pests that attack cereal grains.

Changes in the pattern of distribution of von Willebrand factor in rat aortic endothelial cells following thrombin generation in vivo

The pattern of distribution of von Willebrand factor (VWF) in relatively large sheets of rat aortic endothelial cells (EC) obtained by the Häutchen technique were analysed by immunocytochemistry and light microscopy. EC were examined pre and post administration of a procoagulant mixture of factor Xa (F.Xa) and phosphotidylcholine/phosphotidylserine (PCPS) vesicles which was demonstrated to result in the selective loss of high molecular weight multimers (HMWM) of plasma VWF in the rat. In placebo animals the pattern was heterogenous both in overall distribution and in individual cells which showed both a diffuse and granular pattern. Groups of intensely stained EC were oriented parallel to the longitudinal axis of the aorta and staining was particularly prominent around the orifices of the intercostal arteries, implicating shear-stress as a possible factor in VWF expression by EC. Changes in the pattern of distribution of staining were observed at various time points post-infusion of F.Xa/PCPS, suggesting the immediate release of VWF from EC stores followed by the recruitment of EC to synthesize and store VWF. These changes are consistent with the decrease in EC Weibel-Palade Body (WPB) content observed by EM in previously reported studies using this model.

The platelet cytoskeleton stabilizes the interaction between alphaIIbbeta3 and its ligand and induces selective movements of ligand-occupied integrin

Previously, we showed that a subpopulation of the major platelet integrin, alphaIIbbeta3, co-sediments from detergent lysates with talin and other membrane skeleton proteins. Once alphaIIbbeta3 has bound adhesive ligand in a platelet aggregate, the detergent-insoluble alphaIIbbeta3 redistributes (along with the detergent-insoluble membrane skeleton proteins and a variety of signaling molecules) to a fraction that contains cytoplasmic actin filaments. Concomitantly, certain signaling molecules are activated. The present study shows that, in intact platelets, alphaIIbbeta3 forms clusters when occupied by ligand and is selectively moved into the open canalicular system; alphaIIbbeta3 that has not bound ligand remains diffusely distributed at the periphery of the cell. When cytoplasmic actin filaments are depolymerized by cytochalasins, the ability of alphaIIbbeta3 to bind ligand is decreased, and the movement of ligand-occupied alphaIIbbeta3 is prevented. Together with the previous findings, these results suggest that (i) membrane skeleton-associated alphaIIbbeta3 is selectively induced to bind ligand in activated platelets, (ii) ligand-induced transmembrane signaling causes an altered association of membrane skeleton-associated alphaIIbbeta3 with the cytoplasmic component of the cytoskeleton, (iii) ligand-induced cytoskeletal reorganizations stabilize the interaction between ligand and integrin, and (iv) ligand-occupancy triggers cytoskeletal reorganizations that result in selective movements of occupied ligand.