Effects of Ionic Strength, Salt, and pH on Aggregation of Boehmite Nanocrystals: Tumbler Small-Angle Neutron and X-ray Scattering and Imaging Analysis

The US government currently spends significant resources managing the legacies of the Cold War, including 300 million liters of highly radioactive wastes stored in hundreds of tanks at the Hanford (WA) and Savannah River (SC) sites. The materials in these tanks consist of highly radioactive slurries and sludges at very high pH and salt concentrations. The solid particles primarily consist of aluminum hydroxides and oxyhydroxides (gibbsite and boehmite), although many other materials are present. These form complex aggregates that dramatically affect the rheology of the solutions and, therefore, efforts to recover and treat these wastes. In this paper, we have used a combination of transmission and cryo-transmission electron microscopy, dynamic light scattering, and X-ray and neutron small and ultrasmall-angle scattering to study the aggregation of synthetic nanoboehmite particles at pH 9 (approximately the point of zero charge) and 12, and sodium nitrate and calcium nitrate concentrations up to 1 m. Although the initial particles form individual rhombohedral platelets, once placed in solution they quickly form well-bonded stacks, primary aggregates, up to ∼1500 Å long. These are more prevalent at pH = 12. Addition of calcium nitrate or sodium nitrate has a similar effect as lowering pH, but approximately 100 times less calcium than sodium is needed to observe this effect. These aggregates have fractal dimension between 2.5 and 2.6 that are relatively unaffected by salt concentration for calcium nitrate at high pH. Larger aggregates (>∼4000 Å) are also formed, but their size distributions are discrete rather than continuous. The fractal dimensions of these aggregates are strongly pH-dependent, but only become dependent on solute at high concentrations.

Chest drains – An overview

Chest drains are used in a number of circumstances for the treatment of specific conditions and also for symptomatic relief, and hence insertion of a chest drain can be a life-saving intervention. Therefore, it is imperative that every hospital doctor is familiar with the indications and the principles of safe chest drain insertion. The knowledge of chest drain management following insertion is equally essential. Appropriate chest drain insertion and management underpins the management of chest trauma. Appropriate chest drain management will allow for resolution and management of the underlying clinical condition. This review article outlines the indications, contraindications, and principles of chest drain insertion. Furthermore, it provides an overview of chest drain management and associated complications. Although this review refers to a surgically placed chest drain, the same principles can be applied to a chest drain that is inserted percutaneously.

Myocardial contusion

Myocardial contusion can be a difficult diagnosis to make. There is currently no gold standard of investigation that allows its accurate diagnosis in the clinical setting. Trauma surgeons need to have a high degree of clinical suspicion when dealing with patients who have received blunt thoracic injuries in order that the diagnosis of myocardial contusion may be made. In this article we discuss the diagnosis, potential complications and investigation of patients with suspected myocardial contusion and also present a fl ow diagram for the possible management of patients with trauma who may have suspected myocardial contusion.

Management of rib and sternal fractures

The majority of thoracic injuries encountered in the UK are secondary to blunt trauma following motor vehicle accidents. Rib fractures account for more than half of these injuries. Sternal fractures, although less common, have an increased incidence following the implementation of seat belt legislation. Both rib and sternal fractures may compromise ventilation by a variety of mechanisms. Pain leads to a reduction in lung expansion and sputum retention. Fractured ribs may cause penetrating injury resulting in a haemopneumothorax. There may also be asso ciated pulmonary contusion and flail chest, which further compromises ventilation. Sternal and rib fractures are managed by a number of specialties including accident and emergency staff, cardiothoracic and trauma surgeons, as well as anaesthetists and intensivists. The management of rib and sternal fractures principally consists of the identification and treatment of associated injuries, appropriate respiratory care and symptomatic relief. This article reviews the literature on the investigations and management of the patient with rib and sternal fractures.

Cytomegalovirus as a cause of immunosuppression following aortic valve replacement

The postperfusion syndrome, haemolytic anaemia and thrombocytopenic purpura following open heart surgery have all been attributed to acute cytomegalovirus (CMV) infection,'-3 usually acquired from perioperative transfusions of whole blood. Increased susceptibility of bacterial infections has been described,4 but only in patients who have undergone cardiac transplantation and consequently received immunosuppressive therapy. Studies have shown that CMV can suppress cell-mediated immunity in vivo and in vitro5 and impairment of neutrophil migration has been demonstrated in CMV infected mice.6 We describe a patient with impaired polymorph function associated with an acute CMV infection following aortic valve replacement.

Review article : Mechanical ventricular support in the management of postcardiotomy cardiogenic shock

'For many reasons clinicians hesitate to employ mechanical devices of unproved efficacy except in the most critically ill patients and then only as a desperate measure. These approaches accounted for a substantial lag time between intra-aortic balloon pump availability and widespread utilization. Ventricular assist devices, recently approved for initial clinical trials, face the same dilemmas'. Norman, 1977.1

Successful surgical treatment of Q fever endocarditis with mitral valve repair

We report a case of successful surgical treatment of Q fever endocarditis with mitral valve repair in a 66-year old retired British soldier. Valve replacement is invariably undertaken in Q fever endocarditis due to the degree of valvular damage and concerns about eradicating the organism, Coxiella burnetii. Our unique case allowed valve repair since pre-existing myxomatous degeneration and subsequent posterior mitral valve leaflet prolapse resulted in significant excess valve tissue, allowing quadrangular resection of the damaged and perforated P2 portion of this leaflet. Follow-up at four years (including three years of antibiotic treatment) has confirmed excellent valve repair, with no echocardiographic, clinical or microbiological evidence of recurrence. We are only the second group to describe valve repair in a patient with chronic Q fever endocarditis. Valve repair is preferable to valve replacement for Q fever endocarditis, if technically possible.

Metabolic labeling and immunoprecipitation of yeast proteins

The proteins of Saccharomyces cervsiae can be metabolically labeled, as described here, with (35)methionine and (35)cysteine or a hydrolysate of E. coli labeled with (35)O4(2-). After the labeling, protocols are provided for the mechanical disruption of the yeast cells or conversion to spheroplasts, with subsequent lysis before immunoprecipitation of the proteins.

Traumatic avulsion of the suprascapular artery

Trauma to the subclavian artery and its branches is rare, and usually the result of penetrating injuries. Blunt trauma presents its own peculiar management difficulties, particularly when causing haemorrhage into the thoracic cavity. Cardiothoracic surgeons may be asked to deal with such cases, so an understanding of the anatomy and options for surgical access are essential. We present a case of blunt avulsion of the suprascapular artery resulting in massive haemothorax, a previously unreported injury.

The auxilin-like phosphoprotein Swa2p is required for clathrin function in yeast

BACKGROUND

In eukaryotic cells, clathrin-coated vesicles transport specific cargo from the plasma membrane and trans-Golgi network to the endosomal system. Removal of the clathrin coat in vitro requires the uncoating ATPase Hsc70 and its DnaJ cofactor auxilin. To date, a requirement for auxilin and Hsc70 in clathrin function in vivo has not been demonstrated.

RESULTS

The Saccharomyces cerevisiae SWA2 gene, previously identified in a synthetic lethal screen with arf1, was cloned and found to encode a protein with a carboxy-terminal DnaJ domain which is homologous to that of auxilin. Like auxilin, Swa2p has a clathrin-binding domain and is able to stimulate the ATPase activity of Hsc70. The swa2-1 allele recovered from the original screen carries a point mutation in its tetratricopeptide repeat (TPR) domain, a motif not found in auxilin but known in other proteins to mediate interaction with heat-shock proteins. Swa2p fractionates in the cytosol and appears to be heavily phosphorylated. Disruption of SWA2 causes slow growth and several phenotypes that are very similar to those exhibited by clathrin mutants. Furthermore, the swa2Delta mutant exhibits a significant increase in membrane- associated or -assembled clathrin relative to a wild-type strain.

CONCLUSIONS

These results indicate that Swa2p is a clathrin-binding protein required for normal clathrin function in vivo. They suggest that Swa2p is the yeast ortholog of auxilin and has a role in disassembling clathrin, not only in uncoating clathrin-coated vesicles but perhaps in preventing unproductive clathrin assembly in vivo.

Physiological response in the injured transplant patient

Solid organ transplantation as a treatment for end organ failure is increasing in success. Consequently there are more transplant recipients leading more active lifestyles, resulting in an increasing number presenting as an emergency to hospitals remote from their transplant centre as victims of trauma. A basic knowledge of the anatomy, physiology and pharmacology specific to this group of patients is prerequisite to their successful management. Following a brief history, the incidence and indication for each type of solid organ transplant is detailed, followed by relevant anatomy and physiology. An overview of current immunosuppression and its related side-effects is followed by a discussion concerning vascular access and invasive monitoring.

Organization of the yeast Golgi complex into at least four functionally distinct compartments

Pro-alpha-factor (pro-alphaf) is posttranslationally modified in the yeast Golgi complex by the addition of alpha1,6-, alpha1,2-, and alpha1,3-linked mannose to N-linked oligosaccharides and by a Kex2p-initiated proteolytic processing event. Previous work has indicated that the alpha1,6- and alpha1,3-mannosylation and Kex2p-dependent processing of pro-alphaf are initiated in three distinct compartments of the Golgi complex. Here, we present evidence that alpha1,2-mannosylation of pro-alphaf is also initiated in a distinct Golgi compartment. Linkage-specific antisera and an endo-alpha1,6-D-mannanase (endoM) were used to quantitate the amount of each pro-alphaf intermediate during transport through the Golgi complex. We found that alpha1,6-, alpha1,2-, and alpha1,3-mannose were sequentially added to pro-alphaf in a temporally ordered manner, and that the intercompartmental transport factor Sec18p/N-ethylmaleimide-sensitive factor was required for each step. The Sec18p dependence implies that a transport event was required between each modification event. In addition, most of the Golgi-modified pro-alphaf that accumulated in brefeldin A-treated cells received only alpha1,6-mannosylation as did approximately 50% of pro-alphaf transported to the Golgi in vitro. This further supports the presence of an early Golgi compartment that houses an alpha1,6-mannosyltransferase but lacks alpha1,2-mannosyltransferase activity in vivo. We propose that the alpha1,6-, alpha1,2-, and alpha1,3-mannosylation and Kex2p-dependent processing events mark the cis, medial, trans, and trans-Golgi network of the yeast Golgi complex, respectively.

Techniques in conduit harvesting

Coronary artery bypass grafting is a commonly performed operation for the treatment of ischaemic heart disease. The success of it is largely dependent upon the quality and type of graft used. This article describes the application of and rationale behind techniques commonly used in conduit harvesting.

The high osmolarity glycerol response (HOG) MAP kinase pathway controls localization of a yeast golgi glycosyltransferase

The yeast alpha-1,3-mannosyltransferase (Mnn1p) is localized to the Golgi by independent transmembrane and lumenal domain signals. The lumenal domain is localized to the Golgi complex when expressed as a soluble form (Mnn1-s) by exchange of its transmembrane domain for a cleavable signal sequence (Graham, T. R., and V. A. Krasnov. 1995. Mol. Biol. Cell. 6:809-824). Mutants that failed to retain the lumenal domain in the Golgi complex, called lumenal domain retention (ldr) mutants, were isolated by screening mutagenized yeast colonies for those that secreted Mnn1-s. Two genes were identified by this screen, HOG1, a gene encoding a mitogen-activated protein kinase (MAPK) that functions in the high osmolarity glycerol (HOG) pathway, and LDR1. We have found that basal signaling through the HOG pathway is required to localize Mnn1-s to the Golgi in standard osmotic conditions. Mutations in HOG1 and LDR1 also perturb localization of intact Mnn1p, resulting in its loss from early Golgi compartments and a concomitant increase of Mnn1p in later Golgi compartments.

Platelets and cardiopulmonary bypass

Exposure of blood to an extracorporeal circulation, such as CPB, causes a variety of physiological responses. Haematological derangements are just one of many potential dangers to the patient who undergoes CPB. The paradox of CPB-related problems with the haematological system is that there are some factors tipping the balance towards a bleeding tendency, and others that favour a prothrombotic state. Both of these issues must be dealt with independently to create the safest environment for surgery. It has been demonstrated that platelets play a key role in both haemostatic dysfunction and thrombotic complications of CPB. Much has been achieved, both clinically and in the laboratory, in the understanding of the precise role platelets play in these events, but the exact mechanisms involved have yet to be completely identified. As research progresses, our understanding will increase, but until then clinical practice must be dictated by the current evidence available.

An arf1Delta synthetic lethal screen identifies a new clathrin heavy chain conditional allele that perturbs vacuolar protein transport in Saccharomyces cerevisiae

ADP-ribosylation factor (ARF) is a small GTP-binding protein that is thought to regulate the assembly of coat proteins on transport vesicles. To identify factors that functionally interact with ARF, we have performed a genetic screen in Saccharomyces cerevisiae for mutations that exhibit synthetic lethality with an arf1Delta allele and defined seven genes by complementation tests (SWA1-7 for synthetically lethal with arf1Delta). Most of the swa mutants exhibit phenotypes comparable to arf1Delta mutants such as temperature-conditional growth, hypersensitivity to fluoride ions, and partial protein transport and glycosylation defects. Here, we report that swa5-1 is a new temperature-sensitive allele of the clathrin heavy chain gene (chc1-5), which carries a frameshift mutation near the 3' end of the CHC1 open reading frame. This genetic interaction between arf1 and chc1 provides in vivo evidence for a role for ARF in clathrin coat assembly. Surprisingly, strains harboring chc1-5 exhibited a significant defect in transport of carboxypeptidase Y or carboxypeptidase S to the vacuole that was not observed in other chc1 ts mutants. The kinetics of invertase secretion or transport of alkaline phosphatase to the vacuole were not significantly affected in the chc1-5 mutant, further implicating clathrin specifically in the Golgi to vacuole transport pathway for carboxypeptidase Y.

COPI in ER/Golgi and intra-Golgi transport: do yeast COPI mutants point the way?

Coat complexes facilitate the formation of transport vesicles which are essential for proper trafficking of protein and lipids through the secretory pathway. Since its initial identification in the mid-1980s, the COPI coat complex has been credited with mediating multiple distinct transport events and intracellular processes in the exocytic pathway. Not surprisingly, the diversity of these functions has led to significant debate concerning the primary function of COPI. Specifically, within the ER/Golgi and intra-Golgi systems, does COPI mediate anterograde protein transport, retrograde protein transport, or both? This review will focus on the in vivo roles of COPI, primarily examining data from studies of yeast COPI mutants but also including evidence from mammalian systems as appropriate. Some of the current controversies surrounding whether COPI acts directly or indirectly in anterograde and retrograde transport will also be addressed. Because recruitment of COPI to membranes requires the small GTP-binding protein ARF, we will also discuss ARF and proteins that regulate ARF function, and how these proteins might modulate both COPI-driven events and overall membrane composition. Finally, we will point out some of the links still missing from our understanding of COPI-driven events and discuss possible future directions for studies of COPI function.

von Willebrand factor and urinary albumin excretion are possible indicators of endothelial dysfunction in cardiopulmonary bypass

OBJECTIVE

Experimental evidence suggests that cardiopulmonary bypass (CPB) associated inflammatory response leads to endothelial injury and increased permeability, but this has been difficult to show clinically. We have investigated the use of von Willebrand factor (vWF), and urinary albumin excretion, as measured by the urinary albumin creatinine ratio (ACR), to demonstrate this.

METHODS

A total of 23 patients undergoing elective coronary artery bypass grafting were studied. Complement fragment C3a, leukotrienne B4 (LTB4), interleukin 6 (IL6), neutrophil elastase, vWF and ACR were measured on anaesthetic induction (baseline), 20 min after starting CPB, 5 min after cross-clamp removal, 5 min, 2, 6 and 24 h after termination of CPB. Anaesthetic, CPB and myocardial protection techniques were standardised. ANOVA was performed by using the distribution free Friedman test for each measured parameter. When significance differences were found (P < 0.05), post hoc analysis with Wilcoxon signed rank test was used for comparison of each time point with the base line level and differences were only accepted as significant following the Bonferroni correction (P < 0.008). Summary measures of peak versus peak and area under the cure were also analysed for ACR with vWF.

RESULTS

Peak vs. baseline levels for C3a were 4.9 vs. 2.1 microg/ml (P < 0.0001), LTB4 was 800 vs. 20 pg/ml (P < 0.0001), neutrophil elastase was 250 vs. 115 ng/ml (P < 0.001), IL6 was 620 vs. 1.4 pg/ml (P < 0.0001), vWF was 2.2 vs. 1.3 IU/ml (P < 0.0001) and ACR was 17.6 vs. 2.0 mg/mmol (P < 0.0001). C3a, LTB4 and ACR peaked during the operation. Neutrophil elastase peaked at 2 h following CPB. IL6 and vWF peaked at 6 h following CPB. The correlation coefficient between vWF and ACR following peak versus peak analysis was 0.48 (P = 0.035), and area under the curve analysis was 0.6 (P < 0.01).

CONCLUSION

These results demonstrate that endothelial permeability and injury, as measured by urinary albumin excretion and vWF, respectively, are related and the use of these easily detectable and sensitive biochemical markers warrants further investigation.

ARF is required for maintenance of yeast Golgi and endosome structure and function

ADP ribosylation factor (ARF) is thought to play a critical role in recruiting coatomer (COPI) to Golgi membranes to drive transport vesicle budding. Yeast strains harboring mutant COPI proteins exhibit defects in retrograde Golgi to endoplasmic reticulum protein transport and striking cargo-selective defects in anterograde endoplasmic reticulum to Golgi protein transport. To determine whether arf mutants exhibit similar phenotypes, the anterograde transport kinetics of multiple cargo proteins were examined in arf mutant cells, and, surprisingly, both COPI-dependent and COPI-independent cargo proteins exhibited comparable defects. Retrograde dilysine-mediated transport also appeared to be inefficient in the arf mutants, and coatomer mutants with no detectable anterograde transport defect exhibited a synthetic growth defect when combined with arf1Delta, supporting a role for ARF in retrograde transport. Remarkably, we found that early and medial Golgi glycosyltransferases localized to abnormally large ring-shaped structures. The endocytic marker FM4-64 also stained similar, but generally larger ring-shaped structures en route from the plasma membrane to the vacuole in arf mutants. Brefeldin A similarly perturbed endosome morphology and also inhibited transport of FM4-64 from endosomal structures to the vacuole. Electron microscopy of arf mutant cells revealed the presence of what appear to be hollow spheres of interconnected membrane tubules which likely correspond to the fluorescent ring structures. Together, these observations indicate that organelle morphology is significantly more affected than transport in the arf mutants, suggesting a fundamental role for ARF in regulating membrane dynamics. Possible mechanisms for producing this dramatic morphological change in intracellular organelles and its relation to the function of ARF in coat assembly are discussed.

Prevention of remote organ injury in cardiopulmonary bypass: the impact of flow generation technique

The purpose of this study was to investigate the effects of 3 different types of flow generation for cardiopulmonary bypass on gastrointestinal permeability and on neutrophil expression of CD11b, a surface marker of neutrophil activation. Fourteen patients undergoing elective coronary revascularization were selected randomly to receive 1 of the 3 flow generation techniques (roller, pulsatile, or centrifugal). Intestinal permeability was assessed by the fraction of an oral dose of 51chromium-ethylenediaminetetraacetate (51Cr-EDTA) recovered in the urine over 24 h. Neutrophil activation was determined by expression of CD11b markers at 6 time points. Overall, the 14 patients showed significant increases in intestinal permeability. It was not possible to demonstrate statistically significant differences among the flow generation groups; however, when compared to both roller pump groups, the centrifugal pump group showed a 3.2% reduction in intestinal permeability. There was no change in the expression of CD11b receptors throughout the time points, nor was there a relationship of CD11b markers to the flow generation technique.

Novel approach to investigate a source of microbial contamination of central venous catheters

The potential route of contamination by skin microorganisms onto the distal tip of central venous catheters during insertion was investigated. Thirty patients undergoing cardiac surgery who required a central venous catheter (CVC) as part of their clinical management were studied. Following catheter placement, the device insertion equipment and the skin at the insertion site were sampled for microorganisms. The distal tips of the CVCs were also sampled in situ within 90 min post insertion. Bacteria were isolated from 20 of 30 (66%) CVC skin insertion sites, from 15 of 30 (50%) guidewires, and from five of 30 (16%) catheter distal tips in situ. These findings suggest that despite rigorous skin disinfection and strict aseptic technique, viable microorganisms are impacted during insertion onto the distal tip of the CVC, which may act as a subsequent nidus of infection.

Traumatic disruption of the thoracic aorta: a rational approach to imaging

An imaging strategy is crucial in patients who have sustained a traumatic disruption of the thoracic aorta. Of those who reach hospital alive, 70-90 per cent will survive if diagnosed early and treated appropriately. The clinician has many imaging techniques to choose from, but they vary considerably in their degree of accuracy and performance time. Consequently their appropriateness is dependent on the type of injury suspected, the haemodynamic stability of the patient and the availability and experience of the radiologists. This article describes the types and presentation of traumatic thoracic aortic disruption so that the advantages and disadvantages of the various imaging modalities can be explained. It concludes by presenting an imaging strategy for use when this condition is suspected.

Pentoxifylline preloading reduces endothelial injury and permeability in cardiopulmonary bypass

Pentoxifylline (PTX), a methyl xanthine derivative, reduces endothelial permeability. A double blind, prospective, randomized, placebo controlled, parallel study was undertaken to assess the effect of PTX on leukotriene B4, complement fragment C3a, interleukin 6 (IL6), endothelial injury as measured by von Willebrand factor (vWf), and endothelial permeability as measured by urinary albumin excretion (expressed as excreted urinary albumin to creatinine ratio [ACR]) in patients undergoing cardiopulmonary bypass (CPB) for elective coronary artery bypass grafting. Twenty patients were recruited into each treatment arm and given either PTX 400 mg or placebo three times daily for 1 week before surgery. Patients were well matched. All operations were performed using one anesthetic, CPB, and a myocardial protection technique. Blood and urine samples were taken after anesthetic induction (baseline); 20 min after the start of CPB; 5 min after removal of the cross clamp; and 5 min and 2, 6, and 24 hr after the end of CPB. Pentoxifylline did not reduce IL6, C3a, and LTB4 release but reduced Factor VIIIRAg and urinary albumin excretion preoperatively (PTX vs placebo, ACR 1q.0 vs 2.1 mg/mmol, vWf 0.8 vs 1.3 IU/ml, p < 0.05) and peak levels (PTX vs placebo, ACR 8.9 vs 16.2, vWf 1.2 vs 2.2, p < 0.05) after CPB. These results suggest that PTX may attenuate the endothelial injury and permeability seen in CPB.

Right ventricular failure in patients requiring left ventricular assistance

Right ventricular failure may complicate isolated left ventricular assistance. In a series of 8 patients undergoing left ventricular assistance in postcardiotomy cardiogenic shock, right ventricular failure developed in 5, directly contributing to death in all cases despite initially satisfactory support. Difficulty in grafting a dominant right coronary artery was a common factor in all cases. Early consideration should be given to biventricular support under these circumstances.

Sorting of yeast alpha 1,3 mannosyltransferase is mediated by a lumenal domain interaction, and a transmembrane domain signal that can confer clathrin-dependent Golgi localization to a secreted protein

alpha 1,3 mannosyltransferase (Mnn1p) is a type II integral membrane protein that is localized to the yeast Golgi complex. We have examined the signals within Mnn1p that mediate Golgi localization by expression of fusion proteins comprised of Mnn1p and the secreted protein invertase. The N-terminal transmembrane domain (TMD) of Mnn1p is sufficient to localize invertase to the Golgi complex by a mechanism that is not saturable by approximately 15-20 fold overexpression. Furthermore, the TMD-mediated localization mechanism is clathrin dependent, as an invertase fusion protein bearing only the Mnn1p TMD is mislocalized to the plasma membrane of a clathrin heavy chain mutant. The Mnn1-invertase fusion proteins are not retained in the Golgi complex as efficiently as Mnn1p, suggesting that other signals may be present in the wild-type protein. Indeed, the Mnn1p lumenal domain (Mnn1-s) is also localized to the Golgi complex when expressed as a functional, soluble protein by exchanging its TMD for a cleavable signal sequence. In contrast to the Mnn1-invertase fusion proteins, overexpression of Mnn1-s saturates its retention mechanism, and results in the partial secretion of this protein. These data indicate that Mnn1p has separable Golgi localization signals within both its transmembrane and lumenal domains.

Optimal management of the heart-lung donor

Optimising the management of the heart-lung donor may increase the number of organs suitable for transplantation. This can be achieved by understanding the pathophysiology of brain death and implementing therapeutic measures to counteract the deleterious effect of brain death on end-organ function.

Clathrin-dependent localization of alpha 1,3 mannosyltransferase to the Golgi complex of Saccharomyces cerevisiae

Posttranslational modification of yeast glycoproteins with alpha 1,3-linked mannose is initiated within a Golgi compartment analogous to the medial Golgi cisternae of higher eukaryotes. We have characterized the synthesis, posttranslational modification, and localization of the yeast alpha 1,3 mannosyltransferase (Mnn1p) using antibodies prepared against a segment of this protein expressed in bacteria. Mnn1p is initially synthesized as a 98.5-kD, type II integral membrane glycoprotein that is modified with both N- and O-linked oligosaccharides. It is subject to a slow, incremental increase in molecular mass that is dependent upon protein transport to the Golgi complex. Self-modification of Mnn1p with alpha 1,3 mannose epitopes, primarily on O-linked oligosaccharides, is at least partly responsible for the incremental increase in molecular mass. Mnn1p is a resident protein of the Golgi complex and colocalizes with guanosine diphosphatase to at least two physically distinct Golgi compartments by sucrose gradient fractionation, one of which may be a late Golgi compartment that also contains the Kex2 endopeptidase. Surprisingly, we found that a significant fraction of Mnn1p is mislocalized to the plasma membrane in a clathrin heavy chain temperature sensitive mutant while guanosine diphosphatase remains intracellular. A mutant Mnn1p that lacks the NH2-terminal cytoplasmic tail is properly localized to the Golgi complex, indicating that clathrin does not mediate Mnnlp Golgi retention by a direct interaction with the Mnn1p cytoplasmic tail. These results indicate that clathrin plays a broader role in the localization of Golgi proteins than anticipated.

Signal-mediated retrieval of a membrane protein from the Golgi to the ER in yeast

The Saccharomyces cerevisiae Wbp1 protein is an endoplasmic reticulum (ER), type I transmembrane protein which contains a cytoplasmic dilysine (KKXX) motif. This motif has previously been shown to direct Golgi-to-ER retrieval of type I membrane proteins in mammalian cells (Jackson, M. R., T. Nilsson, and P. A. Peterson. 1993. J. Cell Biol. 121: 317-333). To analyze the role of this motif in yeast, we constructed a SUC2-WBP1 chimera consisting of the coding sequence for the normally secreted glycoprotein invertase fused to the coding sequence of the COOH terminus (including the transmembrane domain and 16-amino acid cytoplasmic tail) of Wbplp. Carbohydrate analysis of the invertase-Wbp1 fusion protein using mannose linkage-specific antiserum demonstrated that the fusion protein was efficiently modified by the early Golgi initial alpha 1,6 mannosyltransferase (Och1p). Subcellular fractionation revealed that > 90% of the alpha 1,6 mannose-modified fusion protein colocalized with the ER (Wbp1p) and not with the Golgi Och1p-containing compartment or other membrane fractions. Amino acid changes within the dily sine motif (KK-->QK, KQ, or QQ) did not change the kinetics of initial alpha 1,6 mannose modification of the fusion protein but did dramatically increase the rate of modification by more distal Golgi (elongating alpha 1,6 and alpha 1,3) mannosyltransferases. These mutant fusion proteins were then delivered directly from a late Golgi compartment to the vacuole, where they were proteolytically cleaved in a PEP4-dependent manner. While amino acids surrounding the dilysine motif played only a minor role in retention ability, mutations that altered the position of the lysines relative to the COOH terminus of the fusion protein also yielded a dramatic defect in ER retention. Collectively, our results indicate that the KKXX motif does not simply retain proteins in the ER but rather directs their rapid retrieval from a novel, Och1p-containing early Golgi compartment. Similar to observations in mammalian cells, it is the presence of two lysine residues at the appropriate COOH-terminal position which represents the most important features of this sorting determinant.

Efficacy of urgent thoracotomy for trauma in patients attended by a helicopter emergency medical service

Over a 12-month period the Helicopter Emergency Medical Service underwent 1084 missions attending casualties in the London area. Sixteen patients required an emergency thoracotomy for resuscitation, nine of which were performed at the scene and seven in the emergency department. The median injury severity score of these patients was 29.9 (SIR 11.8) of which 11 had suffered blunt injuries. Medical attention at scene was administered 16.2 min (SIR 4.0) following the London ambulance service receiving the emergency call. Significantly longer time was spent attending patients who had a scene thoracotomy (35.1 min SIR 16.4) compared with those in whom the thoracotomy was performed in the casualty department. No patient in this series survived resuscitative thoracotomy. It is suggested that scene thoracotomy be abandoned and emphasis placed upon the rapid transport of patients to an emergency facility. This enables other resuscitative measures in addition to thoracotomy to be applied effectively and concentrated over a brief period by a multidisciplinary team.

Atrial fibrillation following myocardial revascularization

Atrial fibrillation following coronary artery surgery is common, especially in elderly patients but despite numerous studies its pathophysiological basis is still incompletely understood. It is usually benign and self-limiting, but may be associated with haemodynamic compromise, prolonged hospitalization and embolic stroke. No risk factors (apart from age and preoperative beta-blocker withdrawal) have been shown to be associated with its occurrence. Conventional treatment is usually effective but no prophylactic regime has been identified. Until such a regime is found the incidence of atrial fibrillation following myocardial revascularization may only be reduced by continuing treatment in patients on beta-blockers in the preoperative period and re-establishing this therapy after surgery.

Left ventricular rupture associated with mitral valve replacement

Rupture of the left ventricle during the immediate postoperative period is a serious, but uncommon complication of mitral valve replacement. This review article outlines the pathological findings, possible causative mechanisms and current management of this cardiac surgical catastrophe.

Hepatic portal venous flow in patients undergoing tricuspid valve surgery

OBJECTIVE

To determine the changes of flow in the hepatic artery and portal vein of patients undergoing tricuspid valve repair together with mitral valve replacement.

DESIGN

Non-randomised parallel group study.

SETTING

Tertiary referral centre.

PATIENTS

18 patients with mitral valve disease with or without tricuspid regurgitation (age range 46-73; six men) and six patients with coronary artery disease and normal left ventricular function (women age range 39-78; four men).

INTERVENTIONS

Mitral valve replacement with or without modified De Vega repair of the tricuspid valve or coronary artery bypass surgery.

MAIN OUTCOME MEASURES

Flow in the hepatic artery and portal vein as measured by duplex Doppler flowmetry before and two to four weeks after operation.

RESULTS

Preoperative hepatic artery flow was less in patients with mitral valve disease than in patients with coronary artery disease (162.7(13.1) ml.min-1 v 242.5(6.6) ml.min-1, p < 0.05). Portal vein perfusion was significantly reduced only in patients with associated tricuspid regurgitation compared with (844(83) ml.min-1 v 1422(64) ml.min-1 p < 0.05). Hepatic perfusion was unaltered after operation in patients undergoing coronary artery bypass surgery (p > 0.05). Flow in the hepatic artery and portal vein was improved only in patients undergoing mitral valve replacement with associated tricuspid valve repair (p < 0.05).

CONCLUSION

Abnormalities of hepatic perfusion can be measured non-invasively in all patients with mitral valve disease but especially in those with associated tricuspid regurgitation needing valve repair. These abnormalities improved two to four weeks after mitral valve surgery and tricuspid valve repair, suggesting that measurement of portal flow might be a useful means of assessing the severity of tricuspid regurgitation.

Current concepts in the use of intra-aortic balloon counterpulsation

Mechanical support of the circulation using intra-aortic balloon counterpulsation has thus far largely been confined to cardiac units. With improved techniques of insertion, many critically ill patients may now benefit. This article reviews the physiology of counterpulsation, the indications and contraindications for its use, and the complications that may occur.

Sternal fractures

Sternal fractures have become more common since the introduction of seat belt legislation. However, the injury often heals well with minimal or no sternal deformity. Morbidity and mortality in patients with fractures of the sternum are usually due to other organ injuries.

Effect of vascular clamp on endothelial integrity of the internal mammary artery

The preservation of endothelial integrity is essential for maintaining patency of vascular grafts. The internal mammary artery flow is often interrupted with the application of a soft vascular clamp to achieve a bloodless field during the anastomosis. We investigated the effect of the vascular clamp on the internal mammary artery endothelium using the scanning electron and light microscope. The endothelium was examined before and at 15 and 30 minutes after clamping in both the pedicled and the skeletonized arteries. Endothelial integrity was breached by clamping with early evidence of platelet adhesion to the damaged areas. The severity of the endothelial damage was related to the clamp time, but there was no difference in the degree of damage between the pedicled and the skeletonized arteries. We conclude that the vascular clamp causes injury to the internal mammary artery endothelium and may be implicated in early postoperative graft failure.

Intrahepatic leiomyosarcoma of the inferior vena cava with extension into the right atrium

We present a case of leiomyosarcoma of the intrahepatic inferior vena cava extending into the right atrium, that has been successfully palliated by removal of the obstructing tumour under conditions of full cardiopulmonary bypass and circulatory arrest. Lesions of this kind have previously thought not to be amenable to surgery. Although resection was incomplete, successful palliation may be achieved facilitating this technique.