Combining Transient Expression and Cryo-EM to Obtain High-Resolution Structures of Luteovirid Particles

The Luteoviridae are pathogenic plant viruses responsible for significant crop losses worldwide. They infect a wide range of food crops, including cereals, legumes, cucurbits, sugar beet, sugarcane, and potato and, as such, are a major threat to global food security. Viral replication is strictly limited to the plant vasculature, and this phloem limitation, coupled with the need for aphid transmission of virus particles, has made it difficult to generate virus in the quantities needed for high-resolution structural studies. Here, we exploit recent advances in heterologous expression in plants to produce sufficient quantities of virus-like particles for structural studies. We have determined their structures to high resolution by cryoelectron microscopy, providing the molecular-level insight required to rationally interrogate luteovirid capsid formation and aphid transmission, thereby providing a platform for the development of preventive agrochemicals for this important family of plant viruses.

Metabolic control of BRISC-SHMT2 assembly regulates immune signalling

SHMT2 regulates one-carbon transfer reactions essential for amino acid and nucleotide metabolism, using PLP as a cofactor. Apo SHMT2 exists as a dimer with unknown functions, whereas PLP binding stabilizes the active, tetrameric state. SHMT2 also promotes inflammatory cytokine signaling by interacting with the BRISC deubiquitylase (DUB) complex, although it is unclear if this function relates to metabolism. We reveal the cryo-EM structure of human BRISC-SHMT2 complex at 3.8 Å resolution. The BRISC complex is a U-shaped dimer of four subunits and SHMT2 sterically blocks the BRCC36 active site and inhibits DUB activity. Only the inactive SHMT2 dimer, but not the active, PLP-bound tetramer binds and inhibits BRISC. BRISC mutations that disrupt SHMT2 binding impaired type I interferon signaling in response to inflammatory stimuli. Intracellular PLP levels regulated BRISC-SHMT2 interaction and inflammatory cytokine responses. These data reveal a new mechanism of metabolite regulation of DUB activity and inflammatory signaling.

An internal thioester in a pathogen surface protein mediates covalent host binding

To cause disease and persist in a host, pathogenic and commensal microbes must adhere to tissues. Colonization and infection depend on specific molecular interactions at the host-microbe interface that involve microbial surface proteins, or adhesins. To date, adhesins are only known to bind to host receptors non-covalently. Here we show that the streptococcal surface protein SfbI mediates covalent interaction with the host protein fibrinogen using an unusual internal thioester bond as a ‘chemical harpoon’. This cross-linking reaction allows bacterial attachment to fibrin and SfbI binding to human cells in a model of inflammation. Thioester-containing domains are unexpectedly prevalent in Gram-positive bacteria, including many clinically relevant pathogens. Our findings support bacterial-encoded covalent binding as a new molecular principle in host-microbe interactions. This represents an as yet unexploited target to treat bacterial infection and may also offer novel opportunities for engineering beneficial interactions.

DOI:http://dx.doi.org/10.7554/eLife.06638.001

The human body is home to many trillions of microbes; most are harmless, but some may cause disease. To live inside a host, microbes must first attach to host tissues. This process involves multiple proteins on each microbe's surface, called adhesins, which interact with the molecules that make up these tissues.

Like all proteins, adhesins are long chains of simpler building blocks called amino acids, and each amino acid is connected to the next via a strong ‘covalent’ bond. Adhesins, however, typically attach bacteria to host molecules through the combined strength of many weak ‘non-covalent’ interactions.

It was recently discovered that one adhesin from a bacterium called Streptococcus pyogenes contains a rare, extra covalent bond—called a thioester—in an unusual location between two of its amino acids. S. pyogenes is a common cause of throat infections in humans, and can also cause the life-threatening ‘flesh-eating disease’.

Walden, Edwards et al. have now used a range of computational, biochemical, structural biology and cell-based techniques to study other adhesins that have thioester bonds in more detail. Computational searches identified hundreds of bacterial proteins containing similar bonds. These included many from bacteria that infect humans: such as Streptococcus pneumoniae, which is the most common cause of pneumonia in adults; and Clostridium difficile, which is notorious for causing severe gut infections in hospital patients. Closer examination of the three-dimensional structures of three of these proteins—including one called SfbI from S. pyogenes—revealed that each had a clear thioester bond. Biochemical tests of an additional nine of the identified proteins strongly suggested they too contained thioester bonds.

Walden, Edwards et al. then showed that SfbI was able to not only attach to tissues like conventional adhesins, but also chemically react with fibrinogen: a human protein that is essential for blood clotting and commonly found in inflamed tissues and healing wounds. This chemical reaction results in the formation of a covalent bond between SfbI and fibrinogen, which is as stable as the bonds that link the amino acids in a protein chain. Further experiments revealed that SfbI strongly binds to human cells grown in the lab under conditions that mimic tissue inflammation. Finally, Walden, Edwards et al. made a mutant version of SfbI that did not contain a thioester, and found that it could not interact with fibrinogen nor bind to human cells.

Together, these findings suggest that thioesters in bacterial adhesins act like ‘chemical harpoons’, which microbes can use to irreversibly attach themselves to molecules within their host's tissues. This attachment mechanism has not been seen before in host-microbe interactions, and further research is now needed to explore whether interfering with this process could represent a new way to treat bacterial infections.

DOI:http://dx.doi.org/10.7554/eLife.06638.002

Covalent host-targeting by thioester domains of Gram-positive pathogens

Gram-positive pathogens are a major concern to global health, with increasing resistance to antimicrobials and the lack of preventative therapeutics. Understanding how these bacteria interact with host cells is vital for the development of novel strategies to combat disease. One of the most crucial steps in infection is adhesion to the host cell. The discovery of complex cell-surface associated proteins, such as pili, has advanced our knowledge of this interaction, however the precise molecular mechanisms underlying this process remain unclear. Structural studies of pili revealed the presence of highly unusual intramolecular covalent bonds between amino acid side chains. These include isopeptide bonds between Lys and Asp/Asn residues, conferring mechanical strength, thermal stability and resistance to proteases [1,2]. In Streptococcus pyogenes pili, the adhesin Spy0125 (or Cpa) interacts with the host cell. It comprises three domains, two of which contain stabilising isopeptide bonds [2,3]. Intriguingly, the third domain contains an extremely rare thioester bond, between a Cys and a Gln residue. A Cys to Ala mutation results in a 75% reduction in adhesion, suggesting that this internal linkage may mediate direct attachment [3]. We have now discovered putative thioester domains (TEDs) in cell-surface proteins of several clinically important pathogens. The only other example of an internal thioester is found in complement proteins, where the reactive bond enables the formation of covalent attachment to pathogens. The presence of these bonds in bacterial proteins suggests the possibility of an as-yet uncharacterised, conserved mechanism of covalent host cell attachment. For a selection of pathogens, we have used mass spectrometry and crystallography to confirm the presence of the covalent link between the Cys and Gln residues within the TEDs. Furthermore, we have identified putative host cell targets of TEDs and confirmed covalent linkages between the TED and the target.

Intramolecular isopeptide but not internal thioester bonds confer proteolytic and significant thermal stability to the S. pyogenes pilus adhesin Spy0125

Streptococcus pyogenes and other Gram-positive bacterial pathogens present long macromolecular filaments known as pili on their surface that mediate adhesion and colonization. These pili are covalent polymers, assembled by sortases. Typically, they comprise a putative adhesin at their tip, a backbone subunit present in multiple copies and a basal subunit that is covalently anchored to the peptidoglycan layer of the cell surface. The crystal structures of pilin subunits revealed the presence of unusual covalent linkages in these proteins, including intramolecular isopeptide and internal thioester bonds. The intramolecular isopeptide bonds in backbone pilins are important for protein stability. Here, using both the wild-type protein and a set of mutants, we assessed the proteolytic and thermal stability of the S. pyogenes pilus tip adhesin Spy0125, in the presence and absence of its intramolecular isopeptide and internal thioester bonds. We also determined a crystal structure of the internal thioester bond variant Spy0125^Cys426Ala. We find that mutations in the intramolecular isopeptide bonds compromise the stability of Spy0125. Using limited proteolysis and thermal denaturation assays, we could separate the contribution of each intramolecular isopeptide bond to Spy0125 stability. In contrast, mutation in the internal thioester bond had a lesser effect on protein stability and the crystal structure is essentially identical to wild type. This work suggests that the internal thioester in Spy0125, although having a minor contributory role, is not required for protein stability and must have a different primary function, most likely mediating a covalent interaction with host cell ligands. Proteins 2014; 82:517–527. © 2013 The Authors Proteins: Structure, Function, and Bioinformatics Published by Wiley Periodicals, Inc.

Structure of the Drosophila melanogaster Rab6 GTPase at 1.4 Å resolution

Rab6 is a small GTPase that belongs to the p21 Ras superfamily. It is involved in vesicle trafficking between the Golgi apparatus and endosomes/ER in eukaryotes. The GDP-bound inactive protein undergoes conformational changes when the nucleotide is exchanged to GTP, allowing Rab6 to interact with a variety of different effector proteins. To further understand how these changes affect downstream protein binding, the crystal structure of Rab6 from Drosophila melanogaster has been solved to 1.4 Å resolution, the highest resolution for a Rab6 structure to date. The crystals belonged to space group C2, with unit-cell parameters a=116.5, b=42.71, c=86.86 Å, α=90, β=133.12, γ=90°. The model was refined to an R factor of 14.5% and an Rfree of 17.3%.

hK5 and hK7, two serine proteinases abundant in human skin, are inhibited by LEKTI domain 6

BACKGROUND

Several skin diseases and atopic disorders including Netherton syndrome and atopic dermatitis have been associated with mutations and deviations of expression of SPINK5, the gene encoding the human 15-domain serine proteinase inhibitor LEKTI. The biochemical mechanisms underlying this phenomenon have not yet been fully clarified.

OBJECTIVES

To identify target proteinases of LEKTI important for processes of desquamation and inflammation of the skin which will enable the development of specific drugs.

METHODS

The inhibitory activities of LEKTI domains 6 and 15 were tested on a number of commercially available serine proteinases and also on the purified kallikreins hK5 and hK7. In addition, recombinant hK5 was used.

RESULTS

LEKTI domain 6 is a potent inhibitor of hK5 and hK7, whereas LEKTI domain 15 exhibits inhibitory activity on plasmin. hK5 and hK7 in particular are relevant to skin disorders.

CONCLUSIONS

The inhibition of hK5 and hK7 by LEKTI domain 6 indicates an important regulatory role of LEKTI in processes of skin desquamation and inflammation, which may explain the severe pathological symptoms associated with abnormalities of SPINK5 and/or its expression. Thus, LEKTI represents a potential drug for the treatment of these disorders.

The 15-domain serine proteinase inhibitor LEKTI: biochemical properties, genomic organization, and pathophysiological role

Proteinases are involved in specific and non-specific proteolytic reactions, and participate in many pathophysiological processes. Normally, they are regulated by endogenously produced proteinase inhibitors which, thus, represent lead structures for the development of therapeutics. We succeeded in partially isolating and cloning a novel human serine proteinase inhibitor which, according to its structure and the expression pattern of the corresponding gene, was termed lympho-epithelial Kazal-type-related inhibitor (LEKTI). This inhibitor is of special interest because it exhibits an extraordinarily large number of 15 potentially inhibitory domains and is of pathophysiological importance for the severe congenital disease Netherton syndrome. Here, we review the as yet known data on protein structure, biochemical properties, genomic organization and gene expression. Furthermore, the relevance of LEKTI for several disorders pointing out its possible future therapeutic value, is discussed.

Purification and characterization of the first archaeal aconitase from the thermoacidophilic Sulfolobus acidocaldarius

The first archaeal aconitase was isolated from the cytosol of the thermoacidophilic Sulfolobus acidocaldarius. Interestingly, the enzyme was copurified with an isocitrate lyase. This enzyme, directly converting isocitrate, the reaction product of the aconitase reaction, was also unknown in crenarchaeota, thus far. Both proteins could only be separated by SDS gel electrophoresis yielding apparent molecular masses of 96 kDa for the aconitase and 46 kDa for the isocitrate lyase. Despite of its high oxygen sensitivity, the aconitase could be enriched 27-fold to a specific activity of approximately 55 micromol x min(-1) x mg(-1), based on the direct aconitase assay system. Maximal enzyme activities were measured at pH 7.4 and the temperature optimum for the archaeal enzyme was recorded at 75 degrees C, slightly under the growth optimum of S. acidocaldarius around 80 degrees C. Thermal inactivation studies of the aconitase revealed the enzymatic activity to be uninfluenced after one hour incubation at 80 degrees C. Even at 95 degrees C, a half-life of approximately 14 min was determined, clearly defining it as a thermostable protein. The apparent K(m) values for the three substrates cis-aconitate, citrate and isocitrate were found as 108 microM, 2.9 mM and 370 microM, respectively. The aconitase reaction was inhibited by the typical inhibitors fluorocitrate, trans-aconitate and tricarballylate. Amino-acid sequencing of three internal peptides of the S. acidocaldarius aconitase revealed the presence of highly conserved residues in the archaeal enzyme. By amino-acid sequence alignments, the S. acidocaldarius sequence was found to be highly homologous to either other putative archaeal or known eukaryal and bacterial sequences. As shown by EPR-spectroscopy, the enzyme hosts an interconvertible [3Fe--4S] cluster.

Influence of practice environment and nurse characteristics on perinatal nurses' responses to ethical dilemmas

BACKGROUND

Previous research on nurses' responses to ethical dilemmas has focused either on nurse characteristics or on practice environment characteristics, but has not examined both influences concurrently.

OBJECTIVE

To explore the relative contributions of practice environment characteristics and nurse personal and professional characteristics to perinatal nurses' willingness to be involved in activities to resolve clinical ethical dilemmas.

METHODS

A descriptive correlational design and hierarchical multiple regression were used to examine responses of 127 perinatal nurses to three instruments: the Nursing Ethical Involvement Scales (NEIS), Perinatal Values Questionnaire (PVQ), and Demographic Data Sheet (DDS).

RESULTS

The organizational variable, nursing influence, accounted for the greatest amount of variance in nurses' reported resolution actions, with nurses' concern about ethics and consequentialist values also contributing significantly. The three predictors together accounted for 31% (24% adjusted) of the variance in actions to resolve clinical ethical dilemmas. Level of nursing education was not a statistically significant influence.

CONCLUSIONS

These results suggest that nurses are more likely to be involved in dilemma resolution activities when they perceive themselves to have higher levels of influence in their practice environments and higher levels of concern about the ethical aspects of clinical situations. Nurses who emphasize consideration of morally relevant aspects of individual patient situations (consequentialist value orientation) and deemphasize adherence to abstract standards, rules, and policies also are more likely to be involved in dilemma resolution.

Problem-based learning in the NICU

Problem-based learning has been used by individuals from various professions and in a wide array of academic and clinical settings. The primary benefits of PBL are that it allows learners to be actively engaged in the learning process and that it can help to strengthen problem-solving skills for learners on any level. PBL can be used effectively in the NICU for both novice and advanced practice nurses.

Autoradiographic identification of a gastrin receptor on the human parietal cell

Gastrin plays an important role in regulating gastric acid secretion and gastrointestinal mucosal growth but its cellular sites of action in man have not been determined. Using cryostat sections of gastric mucosal tissue we have identified (125I-gastrin binding followed by fixation-wet emulsion autoradiography) and characterized (125I-gastrin binding followed by counting) a gastrin receptor binding site in the human stomach. This site displayed binding characteristics similar to those observed in isolated cell systems: specifically, 125I-gastrin binding was rapid (t1/2 approximately 10 min at 37 degrees C), temperature-dependent (3.5 fold more radioligand bound at 22 degrees C than at 4 degrees C) and saturable. The binding of the radioligand was also tissue specific and was five-fold greater in the gastric body than in the gastric antrum and duodenum. In the autoradiographs, silver grains were localized only to parietal cells and not to other epithelial cell types. In the presence of 40 nM gastrin grains were no longer present over parietal cells demonstrating that these sites were both saturable and of high affinity. These data provide the first demonstration of gastrin binding sites (putative receptors) on parietal cells in the human stomach and suggest that gastrin acts directly on these cells to help regulate gastric acid secretion and/or mucosal growth.

A novel gastrin-binding protein in the human eosinophil

A specific and saturable interaction between 125I-gastrin and eosinophils was discovered in autoradiographs of human gastric mucosal tissue and confirmed in isolated and enriched preparations of WBC's. Gastrin displaced 125I-gastrin from eosinophils in a dose-dependent manner with a D50 = 11 uM. Scatchard analysis of the saturation curve indicated a single binding site of low affinity (Kd = 4.14 uM) and high capacity (Bmax = 430 umoles/mg protein). The gastrin binding protein was localized to the granular core of the eosinophil and found to have a molecular weight of approximately 15 kDa following chemical crosslinking of radioligand to granules and SDS/PAGE. Based on its molecular weight and granular location and the charge characteristics of gastrin, the gastrin binding protein in the human eosinophil is most likely major basic protein. In vivo this interaction might act to limit the cytotoxic potential of MBP on tissues and/or attentuate gastrin concentrations thereby helping regulate gastric acid secretion and mucosal growth.

Individualized developmental care for very low-birth-weight infants: a critical review

Developmental care has been widely accepted and implemented in neonatal intensive care units across the country. Its proponents suggest that individualized developmental care is effective in reducing infant morbidity and length of hospital stay and improving neurodevelopmental outcomes. Although individual components of developmental care have been researched in more depth, few studies have examined a total developmental care protocol. This article critically examines the research base on individualized developmental care and discusses implications for clinical practice and future research.

Prenatal screening for hemoglobinopathies. II. Evaluation of counseling

Learning during genetic counseling is often below expectations, especially in the context of genetic screening. In this report we describe learning as a result of genetic counseling of 298 pregnant women identified as hemoglobinopathy carriers, 234 with sickle cell trait and 64 with beta-thalassemia trait. Counseling was designed to provide the information needed in a simple, clear, and nondirective manner. A special videotape produced for this purpose provided dramatization and a role model illustrating an appropriate response. After viewing the videotape the counselee had an opportunity to question the counselor and to have any misconceptions corrected. Questionnaires revealed significantly increased knowledge as a result of counseling in each of the three hemoglobinopathy subject areas tested-namely, clinical manifestations, genetics, and prenatal diagnosis. Five factors correlated with higher knowledge scores after counseling-namely, a younger patient age, more years of education, knowledge of having trait before this identification, knowledge of the baby's father having trait before counseling, and having no prior children.

Prenatal screening for hemoglobinopathies. I. A prospective regional trial

Prenatal hemoglobinopathy screening was chosen as a model system for the study of patient receptivity to unsolicited genetic information. Providers of prenatal care in Rochester, NY, were offered free testing of all their prenatal patients and genetic counseling of women found positive. The 18,907 prenatal samples tested in a 5-year period represented 35.1% of the pregnancies in the Rochester metropolitan region. A hemoglobinopathy was found in 810 pregnancies (4.3%). Of the 21 different types of hemoglobinopathies detected, the most common were sickle cell trait (59%), hemoglobin C trait (19%), beta-thalassemia trait (11%), and hemoglobin E trait (5%). At the time of phlebotomy, 75% of the pregnancies were of less than 18 wk duration. Sixty-six percent of the pregnancies occurred in patients unaware of their diagnosis, and 80% occurred in patients unaware that they might be at risk for a child with a serious blood disorder. Of the 810 positive pregnancies, 551 (68%) occurred in patients who came for counseling. Of 453 women counseled during their first screened pregnancy, 390 (86%) said they wanted their partners tested and 254 (55%) had their partner tested. In the 77 pregnancies thus found to be at risk, the couple was too late for prenatal diagnosis in 12 cases, and the condition for which the fetus was at risk was too mild in 12 cases. Prenatal diagnosis was offered in the remaining 53 pregnancies and was accepted by 25 couples (47%). These results indicate that unselected patients in the primary care setting in this region, even though pregnant, are receptive to and utilize genetic information.

Prenatal screening for hemoglobinopathies. III. Applicability of the health belief model

A comprehensive prenatal hemoglobinopathy screening program in Rochester, NY, has been described in a preceding paper in this issue of the Journal. A woman identified as a carrier may face three decisions. The first is whether to accept the offer of counseling. The second is whether to have her partner tested. If her partner also tests positive, then the third decision is whether to accept the offer of prenatal diagnosis. This report analyzes factors affecting her decision, with special attention being given to factors invoked by the Health Belief Model. Factors predicting that a patient who we identified as a carrier would come for counseling included the following: patient had no prior knowledge that she is a carrier (P less than .001), a gestational age less than 18 wk (P less than .01), and Caucasian race (P less than .05). For sickle cell trait counselees and beta-thalassamia trait counselees, factors found to predict patient's intent to have partner tested were the following: a greater postcounseling knowledge of the disease (P less than .009), a lesser perceived burden of intervention (P less than .011), and belief that the partner is also a carrier (P less than .008). Also for sickle cell trait counselees and beta-thalassemia trait counselees, factors predicting that the partner actually will be tested were the following: living with the partner (P less than .001), gestational age at identification less than or equal to 18 wk (P less than .001), a lesser perceived burden of intervention (P less than .002), and a greater perceived seriousness of the disease (P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Do pregnant women benefit from hemoglobinopathy carrier detection?

A 45% sample of all pregnancies in Rochester, N.Y. over a five-year period showed that 4.2% of pregnant women had a hemoglobinopathy. Sixty-six percent of these women did not know they had such an abnormality, and 80% did not understand its reproductive significance. Sixty-eight percent of women informed they were positive came for counseling. Fifty-seven percent of counseled women had the baby's father tested. Forty-seven percent of couples at risk offered amniocentesis wanted it. (table; see text) A woman was more likely to want her partner tested if she had a more thorough knowledge of the disease or viewed having an affected child as more burdensome. The partner was more likely to come for testing if the couple were living together than if living apart. Prenatal hemoglobinopathy screening is accepted by providers and pregnant women, at least when expert services are provided at no charge to either. Women and couples use the information provided to pursue their reproductive goals.

Nifedipine-haloperidol combination in the treatment of Gilles de la Tourette's syndrome: a case study

Anecdotal case reports have been published describing the use of the calcium channel blockers verapamil and nifedipine to provide rapid and dramatic relief in refractory Gilles de la Tourette's syndrome (TS). The authors' case presentation illustrates that, although these two drugs may not always work alone, they can be successfully used in combination with other medications for treating refractory TS.

Catatonia as a manifestation of paraneoplastic encephalopathy

The psychopathological, electrophysiological, and pathological features of a 58-year-old woman suffering from anaplastic lung carcinoma with paraneoplastic encephalopathy are presented. The predominant behavioral manifestation was a catatonic syndrome that was partially responsive to clonazepam. Although a variety of neurological, psychiatric, and other causes of catatonia have been reported, this is the first reported case of catatonia caused by paraneoplastic encephalopathy.

Prenatal hemoglobinopathy screening: receptivity of Southeast Asian refugees

Because of the availability of safe, accurate prenatal diagnosis for hemoglobinopathies, we wanted to know if pregnant women identified as carriers of a hemoglobinopathy by prenatal screening use this information to determine whether their fetus is at risk. Blood from all pregnant women served by a 40 percent sample of prenatal care providers in Rochester, New York, over 51 months underwent Hb electrophoresis and MCV +/- Hb A2 determination. The frequency of positive was 33/229 (14 percent) for Southeast Asians versus 567/15,824 (3.6 percent) for non-Southeast Asians. Of the positives, 29 (88 percent) Southeast Asians came for counseling versus 348 (61 percent) others. Of those counseled, 26 (90 percent) Southeast Asians had their partners tested, as did 211 (61 percent) others. Of the partners tested, 17 (65 percent) Southeast Asians were also positive compared to 44 (21 percent) others. Of couples offered prenatal diagnosis, 50 percent of each group (4/8 and 17/34) accepted. Of those accepting, all Southeast Asians actually underwent the procedure, while seven (41 percent) others miscarried or failed to keep their appointment. Thus, in our pregnant population, Southeast Asians are four times more likely to be hemoglobinopathy carries than non-Southeast Asians, and Southeast Asian carriers are four times more likely to warrant, want, and undergo prenatal diagnosis for a hemoglobinopathy than non-Southeast Asian carriers.

Source of calcium and cholinergic contraction of the rat portal vein and the sheep coronary artery

To demonstrate the heterogeneity in behavior of the rat portal vein and the sheep coronary artery, we studied the effect of cholinergic stimulation and its dependence upon extracellular ions. Since acetylcholine produces a contraction antagonized by atropine (pA2 9.5), these effects must be mediated by muscarinic receptors. alpha- and beta-adrenergic blocking agents or a drug which destroys noradrenergic nerve endings (6-hydroxydopamine) do not modify the effects of acetylcholine. In a calcium-free medium (EGTA 10(-4) M), the portal vein, unlike the coronary artery, doses not contract to acetylcholine or caffeine. In the coronary artery only the phasic component of the cholinergic contraction is maintained in a calcium-free medium. Verapamil and cobalt abolish the cholinergic contraction of the portal vein, but inhibit only the tonic component in the coronary artery. In a calcium-free medium, hyperosmotic solutions (290 mM sucrose) produce a moderate contraction which occurs slowly in both vessels. In the coronary artery, a sodium-calcium exchange does not appear to participate in the sustained tonic component of the cholinergic contraction. Electron microscopy demonstrates differences between the two blood vessels regarding the size of the sarcoplasmic reticulum. The coronary artery uses calcium both from extra- and intracellular sources. Portal vein is extremely dependent of the extracellular calcium but we were unable to give direct evidence of the utilization of calcium from intracellular pools during the cholinergic contraction of the rat portal vein.

Stress fracture of the navicular bone. Nine cases in athletes

Nine cases of stress fractures of the tarsal navicular bone were treated in athletes. The diagnosis was made with radiographs and bone scan within 6 months. Only two patients were treated surgically. The only poor result was seen in a patient in whom the fracture was only explored.

The binding characteristics of 125I-gastrin and 125I-CCK8 to guinea pig fundic gastric glands differ: is there more than one binding site for peptides of the CCK-gastrin family?

The binding of biologically active 125I-labeled derivatives of the C-terminal octapeptide of cholecystokinin (125I-CCK8) and gastrin (125I-G) to dispersed guinea pig fundic glands were compared at 24 degrees C. Although both peptides share the same C-terminal pentapeptide sequence, differences were found in the amount of each radioligand bound to fundic glands, their dissociation behavior, and their Scatchard plots. However, each peptide was able to displace the other radioligand from the glands at nM concentrations which indicated that both peptides bound to the same site. The different binding characteristics observed for 125I-G and 125I-CCK8 most likely resulted from the different dissociation rates of each peptide.

[Systemic mezlocillin prophylaxis in elective colon surgery]

A prospective randomized, controlled study comprising 100 patients was performed to evaluate the effect of mezlocillin given prophylactically in elective colon surgery. Fifty-two patients were treated and 48 served as controls. Both groups were well-matched for age, sex, disease and surgical procedure. 2 g of mezlocillin were given intravenously before surgery and then every eight hours until the fifth postoperative day. The concentrations of mezlocillin in serum and tissues were determined in 20 patients and related to the MICs of the contaminants and the bacteria isolated postoperatively. A significantly lower incidence of intra-abdominal complications, peritonitis, urinary tract infections and wound infections was found in the mezlocillin group (10%) than in the controls (46%). The average number of postoperative hospital days decreased significantly from 23 days in the control group to 19 days in the mezlocillin group. The analysis of the bacteriological results gave no indication of a selection of resistant strains due to the prophylactic use of mezlocillin. No side-effects were found in connection with mezlocillin prophylaxis.