A low molecular weight outer-membrane protein of Escherichia coli O157:H7 associated with adherence to INT407 cells and chicken caeca

Enterohaemorrhagic Escherichia coli (EHEC) O157:H7 and O26:H11 have been shown to produce a low mol.wt outer-membrane protein (OMP) that is unique to a few serotypes of E. coli. A mutant (A10) of E. coli O157:H7 strain HA1 deficient in the OMP was constructed by TnphoA mutagenesis and assayed for its adherent ability. Adherence of A10 to intestinal epithelial cells (INT407) was significantly less than that of its parent strain (HA1). Adherence of HA1 to INT407 cells was significantly decreased by treatment with a monoclonal antibody (4E8C12) that specifically binds to the OMP. When chickens were infected experimentally with E. coli O157:H7 strains, the average number of cfu of strain A10 recovered from chicken caeca was significantly less than those of strain HA1 and wild-type strain 932 at 14 and 21 days after peroral inoculation. These data suggest that the OMP of EHEC is associated with adherence of E. coli O157:H7 to epithelial cells in vitro and chicken caeca in vivo.

The novel anthracycline annamycin is not affected by P-glycoprotein-related multidrug resistance: comparison with idarubicin and doxorubicin in HL-60 leukemia cell lines

A major factor in limiting the efficacy of anthracyclines is overexpression of the MDR1-encoded p-glycoprotein (p-gp). A new analogue less affected by p-gp is annamycin (ANN), an anthracycline antibiotic with high affinity for lipid membranes and significantly more activity than doxorubicin (DOX). We investigated whether ANN was affected by p-gp-mediated multidrug resistance (MDR) by comparing the cellular accumulation and retention of ANN, idarubicin (IDR), and DOX in the p-gp-negative human leukemia cell lines (HL-60S) and its DOX-selected p-gp-positive subline (HL-60/DOX) with and without verapamil (VER). As expected, HL-60/DOX cells showed lower DOX uptake than HL-60S cells; coincubation with VER (10 mmol/L) increased uptake 2.6-fold restoring it to 100% of uptake in HL-60S cells. IDR uptake increased 1.5-fold in the presence of VER, but ANN was not affected. Coincubation with VER increased DOX retention in HL-60/DOX cells 2.8-fold and IDR retention 1.4-fold; unchanged ANN retention indicated that ANN may overcome p-gp. In the cytotoxicity assay to correlate intracellular anthracycline content with antitumor activity, we found ANN to be less potent than DOX and IDR In sensitive cells, ID 50 being the drug concentration that inhibits cell growth by 50% but its resistance index (RI; ID50 resistant cells divided by ID50 sensitive cells) was lower than that of IDR and DOX (2.6 v 40 and 117.5). Coincubation in the presence of VER resulted in 4.5-fold and 2-fold RI decreases of DOX and IDR, respectively, whereas ANN did not change, further confirming ANN's ability to circumvent p-gp-mediated MDR. Confocal microscopy studies of IDR, ANN, and DOX showed higher intracellular drug compartmentalization for DOX in HL-60/DOX cells incubated in the presence of VER. This study provided evidence that, unlike DOX and IDR, ANN is not affected by p-gp-mediated MDR.

[Cataract surgery in very long axial myopia]

OBJECTIVE

The incidence, refractive characters, operative results and the situations of intraocular lens (IOL) implantation in a series of eyes with very long axial length (> or = 27.00 mm) were analyzed.

METHODS

According to the measurements of preoperative axial length and the degree of implanted IOL, the eyes with lengths of 27.00 mm or more selected from 1,000 eyes of consecutive senile cataract surgery were included in this group. The eyes requiring + 3.00D or more IOL were implanted with IOL. Simple extracapsular cataract extraction was performed on eyes requiring <+3.00D or negative lens. The postoperative follow-up was 20.0 +/- 8.5 months.

RESULTS

There were 81 eyes in this group with a range of axial length of 27.00-34.71 mm and an average corneal curvature of 43.91 +/- 1.81D. The range of IOL power for these eyes was +11.30-11.57D (mean, +2.10 +/- 5.41D). The average axial length of 39 eyes with IOL implantation was 28.04 +/- 0.68 mm and their postoperative corrected visual acuities (PCVA) in 82.1% of eyes were 10/20 or more. The average length of 42 eyes without IOL implantation was 31.68 +/- 1.47 mm and the PCVAs in 42.9% of the eyes were 10/20 or more.

CONCLUSIONS

The myopia with very long axial length is quite common in China. Its operative complications are not frequently seen. The cause of its poor PCVA is due to its pathologic changes in the fundus and the PCVA becomes worse as its axial length is increasing. An IOL with negative power is sometimes necessary for a myopic eye with very long axis.

Differential effects of bFGF on development of the rat retina

A variety of growth factors can influence the expression of differentiated properties by cell types of the developing retina. One unresolved question has been whether these factors can direct the differentiation pathway of uncommitted precursors or whether they act to help the expression of properties by already committed cells. To address this question we have studied the effects of basic fibroblast growth factor (bFGF) on the differentiation of ganglion cells and rod photoreceptors in explant cultures of embryonic rat retinas. Incubation of retinas in the presence of bFGF accelerated the appearance of differentiated ganglion cells and incubation in the presence of anti-bFGF antibodies delayed the appearance. bFGF had no effect on the appearance of differentiated rod photoreceptors as judged by expression of opsin, although all-trans-retinoic acid did increase the number of cells expressing opsin. bFGF inhibited the formation of rod photoreceptor rosettes suggesting that it does influence some properties of rods or the adjacent Müller glial cells. The results suggest that bFGF can alter the timing of differentiation of retinal ganglion cells but not direct their production from retinal precursors.

239 cases of high fever in viral upper respiratory infection (URI) treated with xiang shi qing jie (XSQJ) bag tea

XSQJ bag tea was used to treat 239 cases of high fever caused by viral upper respiratory infection, widely spreading in summer and autumn. For comparison, a control group treated by penicillin combined with Ganmao Qingre Chongji or Banlangen Chongji was set up. The results showed the effect of XSQJ bag tea on the time of abating fever, resolving symptoms and physical signs were significantly better than that of the control group.

CD30 ligand is expressed on resting normal and malignant human B lymphocytes

CD30, a member of the tumour necrosis receptor superfamily, is physiologically expressed on a subpopulation of T helper cells in normal individuals but is also expressed on several malignant and virally transformed cells. Its ligand (CD30L) is a pleiotropic cellular transmembrane protein that can induce cell death in several CD30+ cell lines. CD30L expression has been reported on activated human peripheral blood T lymphocytes and macrophages but not on B cells. Here we show that the CD30L is expressed on resting normal and on malignant B cells in addition to both CD4+ and CD8+ subsets of activated T cells, making it the second tumour necrosis family member, in addition to the CD27 ligand, that can be expressed on both T and B cells. These findings raise the possibility that the CD30L has a role in B-cell/T-cell communication and that B and T cells are likely to be involved in the growth regulation of CD30+ tumours.

Carboxymethyl-dextran-gadolinium-DTPA as a blood-pool contrast agent for magnetic resonance angiography. Experimental study in rabbits

RATIONALE AND OBJECTIVES

The authors evaluate the efficiency of various doses of a paramagnetic macromolecular contrast agent, a gadolinium (Gd)-DTPA-dextran conjugate, as a blood-pool contrast media, in a transverse three-dimensional time-of-flight (TOF) magnetic resonance (MR) angiography sequence of the abdominal aorta in rabbits.

METHODS

Imaging experiments were performed on a 1.5-T magnet, using a transverse three-dimensional TOF tilted optimized nonsaturating excitation (TONE) sequence. The macromolecular contrast media used was a carboxymethyl-dextran-Gd-DTPA (CMD-Gd-DTPA). Different concentrations of CMD-Gd-DTPA (0.005, 0.01, 0.03, 0.05 mmol Gd/kg) were evaluated. A comparative study using Gd-DOTA (0.01 and 0.1 mmol/kg) was performed. A visual analysis based on the gain in the visualized length of small arteries (renal arteries), and a quantitative analysis based on the percent contrast enhancement of the aorta plotted against distance in the slab from the top edge of the acquisition volume were obtained.

RESULTS

A signal-to-noise ratio enhancement of the distal part of the aorta and an improvement in the visualized length of the renal arteries were noted for concentrations of CMD-Gd-DTPA ranging form 0.01 to 0.05 mmol Gd/kg. Venous enhancement was noted for concentrations greater than 0.01 mmol Gd/kg when using CMD-Gd-DTPA or Gd-DOTA.

CONCLUSION

Carboxymethyl-dextran-Gd-DTPA reduced, in part, the saturation effect in a three-dimensional transverse TOF TONE MR angiography in rabbits. To prevent venous enhancement, observed with the higher concentrations used in this study, a decrease in the polydispersity of the polymer should be a goal in the future. Rapid extravasation of the low-molecular weight fraction of the polymer could explain the venous enhancement.

[An analysis of posterior capsular rupture in cataract surgery]

OBJECTIVE

To analyze the incidence, features and related factors of posterior capsular rupture (PCR) in extracapsular cataract extraction, the main intraoperative complication impairing the procedure of intraocular lens (IOL) implantation.

METHODS

The PCR including zonular break and vitreous loss was recorded according to the stage of operative procedure in 757 eyes with senile cataract (the average age was 67.3 +/- 8.3 years).

RESULTS

There were 51 eyes (6.7%) with PCR and 42 eyes (5.5%) of them accompanied with vitreous loss. The PCR in 17 eyes (33.3%) occurred during manual expression of the nucleus, 25 eyes (49.0%) in the course of aspiration of the cortex, and 9 eyes in the subsequent manipulations. Except the unexpected damage to the posterior capsule, the main factors were: smaller incision for the nucleus expression, lens dislocation during capsulotomy, small pupil in the course of cortex aspiration, high pressure from the posterior chamber and traction on capsular bag when removing anterior part of the cortex.

CONCLUSION

Intraoperatively, the prevention of PCR and improvement of management ability are very important for the IOL I-stage implantation.

Motif identification neural design for rapid and sensitive protein family search

A new method, the motif identification neural design (MOTIFIND), has been developed for rapid and sensitive protein family identification. The method is an extension of our previous gene classification artificial neural system and employs new designs to enhance the detection of distant relationships. The new designs include an n-gram term weighting algorithm for extracting local motif patterns, an enhanced n-gram method for extracting residues of long-range correlation, and integrated neural networks for combining global and motif sequence information. The system has been tested and compared with several existing methods using three protein families, the cytochrome c, cytochrome b and flavodoxin. Overall it achieves 100% sensitivity and > 99.6% specificity, an accuracy comparable to BLAST, but at a speed of approximately 20 times faster. The system is much more robust than the PROSITE search which is based on simple signature patterns. MOTIFIND also compares favorably with BLIMPS, the Hidden Markov Model and PROFILESEARCH in detecting fragmentary sequences lacking complete motif regions and in detecting distant relationships, especially for members of under-represented subgroups within a family. MOTIFIND may be generally applicable to other proteins and has the potential to become a full-scale database search and sequence analysis tool.

A conformational change in the methyltransferase from Clostridium thermoaceticum facilitates the methyl transfer from (6S)-methyltetrahydrofolate to the corrinoid/iron-sulfur protein in the Acetyl-CoA pathway

The methyltetrahydrofolate:corrinoid/iron-sulfur protein methyltransferase (MeTr) from Clostridium thermoaceticum catalyzes the methylation of a corrinoid/iron-sulfur protein (C/Fe-SP) by the N5 methyl group of (6S)-methyltetrahydrofolate (CH3-H4folate). This is an important reaction in the reductive acetyl-CoA pathway. The forward and reverse reactions of MeTr have a pH dependence that appears to reflect protonation of a group on the protein [Zhao, S., Roberts, D. L., & Ragsdale, S. W. (1995) Biochemistry 34, 15075-15083]. In the work reported here, fluorescence and rapid reaction kinetics were used to demonstrate that this protonation elicits a rate-limiting conformational change. As the pH was lowered, the emission maximum for intrinsic tryptophan fluorescence underwent a red shift (pK(a) = 5.4) and the emission intensity increased (pK(a) = 5.1). The extrinsic fluorescence probe, 4,4'-bis-1-phenylamino-8-napthalenesulfonate (bis-ANS) was used to report on the conformational change. The bis-ANS fluorescence was strongly enhanced upon binding MeTr. As the pH was decreased, the fluorescence was further enhanced and the emission maximum underwent a 14 nm blue shift (pK(a) = 5.0). By stopped-flow fluorescence studies, it was shown that these fluorescence changes occur at rates similar to the k(cat) for the MeTr reaction and thus reflect catalytically competent events. The combined results indicate that CH3-H4folate binds to a hydrophobic region in MeTr that includes a tryptophan residue(s). MeTr undergoes a pH-dependent conformational change that exposes this region to solvent and facilitates substrate binding.

Preliminary study on the molecular structure of 3' region of Duchenne muscular dystrophy (DMD) gene in Chinese

Number and order of HindIII exon-containing fragments (Hd) at 3' region of DMD gene were studied systematically using 16 partly-overlapping cDNA subprobes which were produced from dystrophin cDNA 9-14 with each of 9 restriction endonucleases. There are 25 Hd fragments corresponding to cDNA 9-14 in DMD gene. Since then, the exact length and the new order of Hd fragments are established. A new 2.1 kb fragment (Hd 55) is revealed; a 5.2 kb fragment (formerly designated as Hd 59) is excluded and the existence of a controversial 3.2 kb fragment (Hd 64) is confirmed. Besides, three new exons were revealed by comparing the PvuII and the XbaI hybridization patterns with the HindIII hybridization patterns for these cDNA subprobes. It is concluded that there are at least 66 Hd fragments, or 79 exons in DMD gene basing on the discovery of three additional exons. The corresponding relationship between the 66 Hd fragments and the SfiI large scale physical map has been studied, and at least 17 Hd fragments or 19 exons were shown to be distributed in the last fragment (IJ fragment) of the SfiI map of DMD gene.

Monoclonal antibodies specific for rat relaxin. IX. Evidence that endogenous relaxin promotes growth of the vagina during the second half of pregnancy in rats

It is established that endogenous relaxin promotes the growth and development of the cervix, mammary glands, and nipples in pregnant rats. Additionally, the observation that porcine relaxin promotes growth of the vagina in both nonpregnant and pregnant rats provides indirect evidence that endogenous relaxin may effect growth of the vagina during rat pregnancy. The purpose of this study was to determine whether endogenous relaxin promotes growth of the vagina in pregnant rats. To that end, a monoclonal antibody, specific for rat relaxin, designated MCA1, was used to passively neutralize endogenous relaxin throughout the second half of pregnancy in intact rats. Five milligrams of highly purified MCA1 were injected iv to rats daily from days 12-22 of pregnancy. Controls received either a monoclonal antibody for fluorescein or PBS. The vaginal wet weight, dry weight, length, diameter, inner surface area, DNA content, and percent water content were determined. No differences were found between monoclonal antibody for fluorescein and PBS controls for any of the measured vaginal parameters. In contrast, values for all physical parameters, except percent water content, were significantly lower in MCA1-treated rats than in controls. Vaginal DNA content was also lower in MCA1-treated rats than in controls; and this observation supports the view that relaxin induces vaginal growth at least in part by promoting cell proliferation. To examine the mechanism of relaxin's apparent action on the vagina, specific relaxin-binding sites were localized immunohistochemically. Relaxin-binding sites were found in epithelial and smooth muscle cells, and the binding was specific for relaxin. We conclude that endogenous relaxin promotes growth of the vagina in pregnant rats.

Affinity chromatography of regulatory subunits of protein phosphatase-1

In this study we demonstrate that recombinant rabbit muscle protein phosphatase-1 immobilized on CH-Sepharose is an efficient affinity chromatography support for the isolation of subunits of phosphatase-1. The support was used to isolate the glycogen binding subunit of phosphatase-1 from muscle and nonmuscle rat tissues. Examination of the affinity-purified material from rat heart and liver showed that the major component was a 160-kDa polypeptide on SDS-PAGE. The identity of the purified liver 160-kDa polypeptide as the glycogen binding subunit was confirmed by the demonstration that it is capable of binding to glycogen, and is phosphorylated by the catalytic subunit of PKA. The novel observation was made that the phosphorylation was dependent on the presence of glycogen. Examination of the material from heart, lung, liver, kidney, and brain showed a similar phenomenon. Our studies show that this subunit is widely distributed in tissues. The affinity support was also efficient in the isolation of the NIPP-1 (nuclear inhibitor of protein phosphatase-1) proteins from calf thymus. Examination of heat-treated extracts of rat liver led to the isolation of a novel 19-kDa inhibitory protein which could also be phosphorylated by PKA and may represent the rat liver homolog of calf thymus NIPP-1.

[Effects of capsules on attachment of human periodontal ligament fibroblasts to root surface]

Inhibition of attachment of human periodontal ligament fibroblasts to root surface by three capsules were determined with the methods of trypan blue and L*a*b* color difference measurement. The results showed that capsule from porphyromonas gingivalis was the strongest one in inhibiting attachment and followed by the one from provotalla intermedia. Capsule from porphyromonas endodontolis was the weakest one. The values of color difference from that of control root surface were 11, 13, 8.28 and 4.09 respectively. Inhibitory mechanism of capsules may include a direct growth inhibition of fibroblasts and a decrease in attachment due to changes of root surface properties. There were a few fibroblasts attached to root surface with progressive periodontitis, this was a sharp contrast with that of control root surface. We deduce that long term affections of toxins including capsules and other substances led to changes of root surface with periodontitis, which made fibroblasts difficult to attach.

A protein class database organized with ProSite protein groups and PIR superfamilies

A protein class (ProClass) database is developed as a "value-added" "second-generation" database organized according to family relationships. The database collects non-redundant protein sequence entries from SwissProt and PIR databases, and classifies them in families defined collectively by the ProSite protein groups and PIR superfamilies. The major objectives of the database are to maximize family information retrieval, to provide speedy family identification, and to help organizing existing protein sequence databases. The database has two sub-databases: PCFam (ProClass Family) to define protein families and provide links to ProSite patterns and PIR superfamilies, and PCSeq (ProClass Sequence) to describe sequence entries and provide links to PCFam, SwissProt, PIR, and ProSite databases. The current ProClass release has a total of 85,165 sequence entries, about half of which are classified in 3072 ProClass families; it also contains 10,431 newly established SwissProt-PIR links. The database can help reveal domain structures of related families, define new ProSite and PIR families, and provide family assignments for unclassified sequence entries. New ProSite and PIR family members are readily identified via database cross-reference, including 9437 SwissProt entries and 8522 PIR entries. False negative family members missed by both ProSite and PIR are detected using a neural network family identification system. The newly identified superfamily memberships are being incorporated into the current PIR database releases in a collaborative effort with the PIR. The ProClass database is accessible through anonymous FTP and on-line search on the World Wide Web.

Effect of creatine supplementation on intramuscular TCr, metabolism and performance during intermittent, supramaximal exercise in humans

This study examined the effect of (a) creatine supplementation on exercise metabolism and performance and (b) changes in intramuscular total creatine stores following a 5 day supplementation period and a 28 day wash-out period. Six men performed four exercise trials, each consisting of four 1 min cycling bouts, punctuated by 1 min of rest followed by a fifth bout to fatigue, all at a workload estimated to require 115 or 125% VO2,max. After three familiarization trials, one trial was conducted following a creatine monohydrate supplementation protocol (CREAT); the other after 28 d without creatine supplementation, in which the last 5 d involved placebo ingestion (CON). Intramuscular TCr was elevated (P < 0.05) in CREAT compared with the final familiarization trial (FAM 3) and CON. Concentrations of this metabolite in these latter trials were not different. In addition, a main effect (P < 0.05) for treatment was observed for PCr when the data from CREAT were compared with CON. In contrast, no differences were observed in the total adenine nucleotide pool (ATP+ADP+AMP), inosine 5'-monophosphate, ammonia, lactate or glycogen when comparing CREAT with CON. Despite the differences in TCr and PCr concentrations when comparing CREAT with other trials, no difference was observed in exercise duration in the fifth work bout. These data demonstrate that creatine supplementation results in an increase in TCr but this has no effect on performance during exercise of this nature, where the creatine kinase system is not the principal energy supplier. In addition 28 d without supplementation is a sufficient time to return intramuscular TCr stores to basal levels.

Mechanistic studies of the methyltransferase from Clostridium thermoaceticum: origin of the pH dependence of the methyl group transfer from methyltetrahydrofolate to the corrinoid/iron-sulfur protein

A methyltetrahydrofolate:corrinoid/iron-sulfur protein methyltransferase (MeTr) from Clostridium thermoaceticum catalyzes the transfer of the N5 methyl group from (6S)-methyltetrahydrofolate (CH3-H4folate) to the cobalt center of a corrinoid/iron-sulfur protein (C/Fe-SP). The methylcobamide product is the first in a series of enzyme-bound organometallic intermediates in the acetyl-CoA pathway of anaerobic CO2 fixation. The mechanisms of the forward and reverse reactions with CH3-H4folate and either the C/Fe-SP or vitamin B12 as substrates were studied by steady-state and pre-steady-state kinetics. This ability to effectively utilize free cobalamin as well as the C/Fe-SP in the transmethylation appears to explain why [14C]methylcobyric acid was found as a product of labeling C. thermoaceticum cells with 14CO2 [Ljungdahl, L. G., Irion, E., & Wood, H. G. (1965) Biochemistry 4, 2771-2780]. Stopped-flow experiments indicate that the Co(I)-C/Fe-SP performs a direct SN2 displacement of the methyl group of CH3-H4folate to form H4folate and methyl-Co(III). The pre-steady-state rate constants in the forward and reverse reactions increased as the pH was lowered (pKa approximately 5.5). Similar pH profiles were obtained by steady-state kinetics. The kcat/Km values for the C/Fe-SP and CH3-H4folate in the forward direction and for the methylated C/Fe-SP and H4folate in the reverse direction increased as the pH was lowered (pKa approximately 5.3). A different pH profile was obtained with free cobalamin as the substrate; the kcat/Km for CH3-H4folate and cobalamin (forward reaction) increased (pKa approximately 7.0) and the kcat/Km for H4folate and methylcobalamin (reverse reaction) decreased (pKa approximately 5.3) as the pH was lowered.(ABSTRACT TRUNCATED AT 250 WORDS)

Enzyme reactions in the presence of cyclodextrins: biosensors and enzyme assays

Cyclodextrins, macrocyclic carbohydrates with apolar internal cavities, can form complexes with, and solubilize many normally water-insoluble compounds. Ferrocene and its derivatives, tetrathiafulvalene and tetramethylbenzidine, can function as redox mediators, but are insoluble in water; when they are complexed with cyclodextrins, they can be used in enzymatic assays and in the construction of mediated biosensors. In addition, the solubilization of polynuclear aromatic hydrocarbons (PAHs), including the potent carcinogen benzo[a]pyrene, by cyclodextrins has enabled the detection of these important environmental contaminants.

Preliminary X-ray crystallographic study of methyltetrahydrofolate: corrinoid/iron sulfur protein methyltransferase fromClostridium thermoaceticum

Methyltetrahydrofolate:corrinoid/iron sulfur protein methyltransferase from Clostridium thermoaceticum has been crystallized in two polymorphic forms and characterized by X-ray diffraction measurements. Form I displayed orthorhombic symmetry with a = 63.9, b = 53.8, c = 164.0 A. Form II also displayed orthorhombic symmetry with a = 63.5, b = 87.1, c = 117.9 A. Crystals of form I diffract to approximately. 3 A resolution; those of form II diffract to approximately 2.7 A.

Cloning and nucleotide sequence of a gene upstream of the eaeA gene of enterohemorrhagic Escherichia coli O157:H7

A DNA segment located immediately upstream of the eaeA gene of enterohemorrhagic Escherichia coli O157:H7 strain HA1 was cloned and sequenced. This segment contained an open reading frame encoding a predicted protein of 156 amino acids. A database search identified similar open reading frames upstream of the eaeA gene in two other bacterial pathogens, i.e. enteropathogenic E. coli and Citrobacter freundii. The predicted amino acid sequence of the enterohemorrhagic E. coli protein shared 96.8% and 94.2% identity with the enteropathogenic E. coli and C. freundii sequences, respectively. Because the open reading frame is located within the locus of enterocyte effacement region of the E. coli chromosome, a 'hot spot' for insertion of virulence factor genes, and shares high sequence homology with attaching and effacing EPEC and C. freundii, this protein may be associated with pathogenicity of E. coli O157:H7.

Synergistic effects of fluid shear stress and cyclic circumferential stretch on vascular endothelial cell morphology and cytoskeleton

The development of atherosclerosis is thought to be initiated by a dysfunctional state of the vascular endothelium. The proposal that mechanical forces play a role in the localization of this disease has led researchers to develop in vitro models to assess their effects on cultured endothelial cells. The arterial endothelium is exposed simultaneously to circumferential hoop stretch and wall shear stress, yet previous investigations have focused on the isolated effects of either cyclic stretch or shear stress. The influence of physiological levels of combined shear stress and hoop stretch on the morphology and F-actin organization of bovine aortic endothelial cells was investigated. Cells subjected for 24 hours to shear stresses higher than 2 dyne/cm2 or to hoop stretch greater than 2% elongated significantly compared with unstressed controls and oriented along the direction of flow and perpendicular to the direction of stretch. Exposure to more than 4% stretch significantly enhanced the responses to shear stress. Both shear stress and hoop stretch induced formation of stress fibers that were aligned with the cells' long axes. Simultaneous exposure to both stimuli appeared to enhance stress fiber size and alignment. These results indicate that shear stress and hoop stretch synergistically induce morphological changes in endothelial cells, which suggests that circumferential strain might modulate sensitivity of endothelial cells towards shear stress.