Radiation exposure of orthopaedic trainees: quantifying the risk

Interest in radiation protection issues has recently grown within the medical profession. Several investigators have examined the radiation exposure of orthopaedic surgeons using X-rays during trauma surgery, and found that doses received are within acceptable limits. These studies however, have been performed over short time-periods or have been confined to single procedures only. In this paper, we report the results of monitoring of the total exposure across all procedures of a group of orthopaedic surgeons over a 4-month period. Doses received were all below the International Commission on Radiological Protection (ICRP) recommended limits. While these results are reassuring, they do not represent grounds for complacency. Continued vigilance will be essential as work practices continue to change. In orthopaedics, in contrast with other specialties, the limiting dose is that to the hands. In view of this finding, extremity dosimetry for surgeons regularly using X-rays in theatre should be considered.

Overexpression of the vaccinia virus A38L integral membrane protein promotes Ca2+ influx into infected cells

The vaccinia virus Western Reserve A38L protein is a hydrophobic integral membrane glycoprotein with amino acid similarity to mammalian integrin-associated protein. The protein has an N-terminal immunoglobulin superfamily domain, followed by five membrane-spanning domains and a short cytoplasmic tail. Deletion of the protein reduces virus plaque size but does not affect virus virulence (J. E. Parkinson, C. M. Sanderson, and G. L. Smith, Virology, in press). In this study, we have used a recombinant vaccinia virus in which the A38L gene may be inducibly overexpressed by addition of isopropyl-beta-D-thiogalactopyranoside (IPTG), to demonstrate that overexpression of the vaccinia virus A38L gene produces drastic changes in the morphology, permeability, and adhesion of infected cells. In particular, A38L overexpression caused swelling of cells, marginalization of nuclear chromatin, and vacuolization of the endoplasmic reticulum, features characteristic of cell necrosis. By 18 h postinfection, cells become permeable and lytic as defined by the free entry of propidium iodide and loss of the cytoplasmic enzyme lactate dehydrogenase. Chelation of extracellular Ca2+ 22 h postinfection inhibited further release of lactate dehydrogenase, showing that Ca2+ influx was required for A38L-induced lysis. Direct measurement of 45Ca2+ influx showed that the rate of Ca2+ uptake was directly related to the period of A38L induction. The A38L protein, therefore, promotes the formation of pores within the plasma membrane of cells, and these pores facilitate Ca2+ entry and induce necrosis. Addition of rifampin inhibited virus assembly but not the ability of A38L to induce necrosis, indicating that pore formation is independent of viral morphogenesis. Finally, overexpression of the A38L protein resulted in a reduced plaque size and a threefold decrease in production of infective particles in vitro. The A38L protein represents the first example of a virus protein which directly or indirectly promotes the influx of extracellular Ca2+.

Vaccinia virion protein I8R has both DNA and RNA helicase activities: implications for vaccinia virus transcription

A nucleic acid-dependent ATPase was purified from vaccinia virions and shown to have both DNA:DNA and RNA:RNA helicase activities. This is only the third helicase to be identified that can unwind both DNA and RNA duplexes. The DNA helicase activity copurified with nucleoside triphosphate phosphohydrolase II (NPHII), an RNA helicase encoded by gene I8R (S. Shuman, Proc. Natl. Acad. Sci. USA 89:10935-10939, 1992). Immunodepletion with two antisera to NPHII and analysis of recombinant NPHII protein (C. H. Gross and S. Shuman, J. Virol. 69:4727-4736, 1995) confirmed that the DNA helicase activity was encoded by the I8R gene. The I8R DNA helicase unwound DNA in a 3'-to-5' direction only, unwound duplexes of 35 bp but not 45 bp, and could be stimulated to unwind longer duplexes by the Escherichia coli single-stranded DNA-binding protein. DNA helicase activity was not stimulated by salt and was sensitive to 100 mM NaCl or KCl. The I8R protein has amino acid similarity to human RNA helicase A and to nuclear DNA helicase II, a bovine DNA and RNA helicase. On the basis of the phenotype of I8R temperature-sensitive mutants, it was suggested that the I8R protein is not required for DNA replication but might aid in the extrusion of early mRNA from the virus core. The DNA helicase activity of the I8R protein allows another interpretation of the mutant phenotype, namely, that the I8R DNA helicase activity is required for initiation of early transcription from within vaccinia virions.

Predictive validity of the suicide probability scale among adolescents in group home treatment

OBJECTIVE

To determine the predictive validity of the Suicide Probability Scale (SPS).

METHOD

Prospective design, predicting subsequent suicide attempts, suicide verbalizations, and minor self-destructive behaviors from SPS scores at admission to a group home in a sample of 855 adolescents.

RESULTS

SPS scores significantly predicted all three suicide-relevant measures. Only 48% of subsequent attempts could have been predicted from SPS criteria that would have put 21% of newly admitted adolescents in the at-risk group. Although the prediction is far from perfect, it can prevent some suicide attempts when combined with effective suicide precautions.

CONCLUSIONS

This is the first known evidence of predictive validity of any measure of suicide risk in adolescents. Its predictive ability may have been reduced by interventions designed to reduce suicide risk. Despite the large number of false-positives and modest predictive validity, a large body of literature indicates that quantitative predictions perform better than clinical judgments in predicting psychological outcomes. However, the SPS measures only a subset of factors predictive of suicide, including suicidal ideation, hopelessness, and social isolation. Risk factors not assessed by the SPS include previous suicide attempts, conduct disorder, substance abuse, and reasons for living. These additional risk factors may be important to improve upon the predictive validity of the SPS.

Vaccinia virions lacking core protein VP8 are deficient in early transcription

When synthesis of the 25-kDa vaccinia virus core protein VP8 is repressed, mature virus particles of normal appearance are produced to approximately 80% of wild-type levels but these particles are over 100-fold less infectious than wild-type particles (D. Wilcock and G. L. Smith, Virology 202:294-304, 1994). Here we show that virions which lack VP8 can bind to and enter cells but the levels of steady-state RNA are greatly reduced in comparison with those for wild-type infections. In vitro assays using permeabilized virions demonstrated that VP8-deficient virions had drastically reduced rates of transcription (RNA synthesis was decreased by 80 to 96%) and that the extrusion of RNA transcripts from these virions was also decreased. Low concentrations of sodium deoxycholate extracted proteins more efficiently from VP8-deficient virions than from wild-type virions. The increased fragility of VP8-deficient virions and their slower RNA extrusion rates suggest that VP8 may be required for the correct formation of the core. Virions which lack VP8 were shown to contain a full complement of transcription enzymes, and soluble extracts from these virions were active in transcription assays using either single-stranded M13 DNA or exogenous plasmid template containing a vaccinia virus early promoter. Thus, the defect in transcription is due not to a lack of specific transcriptional enzymes within virions but rather to the inability of these enzymes to efficiently transcribe the DNA genome packaged within VP8-deficient virions. These results suggest that VP8 is required for the correct packaging of the viral DNA genome and/or for the efficient transcription of packaged virion DNA, which has a higher degree of structural complexity than plasmid templates. Possible roles for VP8 in these processes are discussed.

Comparative effects of inorganic phosphate and oxalate on uptake and release of Ca2+ by the sarcoplasmic reticulum in saponin skinned rat cardiac trabeculae

1. Ventricular trabeculae from the right ventricle of rat heart were suspended in a 6 microliters bath and "skinned' with saponin (50 mg ml-1). Preparations were perfused with solutions mimicking the intracellular milieu and the [Ca2+] within the bath was monitored continuously using fura-2. 2. Application of 20 mM caffeine released Ca2+ from the sarcoplasmic reticulum (SR), resulting in a transient increase in the fura-2 fluorescence ratio. Caffeine-induced Ca2+ transients were smaller in the presence of 30 or 60 mM inorganic phosphate (Pi). This depressive effect of Pi on SR function was reversed by 10 mM creatine phosphate (CP). Caffeine-induced Ca2+ transients were also reduced in the presence of 10 mM oxalate, although this effect was not reversed by CP. 3. When perfusion was stopped in the presence of 30 or 60 mM Pi, the [Ca2+] within the bath remained constant. However, when the flow was stopped in the presence of 60 mM Pi and 10 mM CP, a prolonged decrease in [Ca2+] occurred, consistent with precipitation of calcium phosphate within the SR. A similar decrease in [Ca2+] was observed when perfusion was stopped in the presence of 2 or 20 mM oxalate, in the absence or presence of CP. 4. The SR was Ca2+ depleted by withdrawal of ATP and exposure to 20 mM caffeine. Perfusion was then stopped and ATP reapplied, resulting in a maintained decrease in [Ca2+] within the bath, due to SR Ca2+ uptake. Net Ca2+ uptake was markedly reduced in the presence of 30 mM Pi. In contrast, 20 mM oxalate increased Ca2+ uptake and the [Ca2+] within the bath continued to fall over 2-3 min. 5. Introduction of Pi released Ca2+ from the SR. Ryanodine (100 microM) abolished caffeine-induced Ca2+ release while Pi-induced Ca2+ release was unaffected. Pi-induced Ca2+ release was reduced in the constant presence of 20 mM caffeine or 10 mM CP and was abolished completely by disruption of the SR membrane with Triton X-100. Pi-induced Ca2+ release occurred after abolition of SR Ca2+ uptake by ATP withdrawal. 6. These results suggest that the Pi-induced decrease in releasable Ca2+ does not result from precipitation of calcium phosphate within the SR lumen. Pi inhibits net SR Ca2+ uptake, but this appears to result from activation of a ryanodine-insensitive Ca2+ efflux pathway rather then inhibition of Ca2+ uptake. Possible mechanisms are considered, including reversal of the SR Ca2+ pump.

Vaccinia virus glycoprotein A34R is required for infectivity of extracellular enveloped virus

The vaccinia virus strain Western Reserve (WR) A34R gene encodes a C-type lectin-like glycoprotein, gp22-24, that is present in the outer membrane of extracellular enveloped virus (EEV) with type II membrane topology (S.A. Duncan and G.L. Smith, J. Virol. 66:1610-1621, 1992). Here we that a WR A34R deletion mutant (WR delta A34R) released 19- to 24-fold more EEV from infected cells than did WR virus, but the specific infectivity of the released virions was reduced 5- to 6-fold. Rupture of the WR delta A34R EEV outer envelope by freeze-thawing increased virus infectivity by five- to sixfold, because of the release of infectious intracellular mature virus. All other known EEV-specific proteins are incorporated into WR delta A34R EEV, and thus the loss of gp22-24 is solely responsible for the reduction of EEV specific infectivity. The WR delta A34R virus is highly attenuated in vivo compared with WR or a revertant virus in which the A34R gene was reinserted into WR delta A34R. This attenuation is consistent with the known important role of EEV in virus dissemination and virulence. Vaccinia virus strain International Health Department-J (IHD-J) produces large amounts of EEV and forms comets because of an amino acid substitution within the A34R protein (R. Blasco, R. Sisler, and B. Moss, J. Virol. 67:3319-3325, 1993), but despite this, IHD-J EEV has a specific infectivity equivalent to that of WR EEV. Substitution of the IHD-J A34R gene into the WR strain induced comet formation and greater release of EEV, while coexpression of both genes did not; hence, the WR phenotype is dominant. All orthopoxviruses tested express the A34R protein, but most viruses, including variola virus, have the WR rather than the IHD-J A34R genotype. The A34R protein affects plaque formation, EEV release, EEV infectivity, and virus virulence.

The vaccinia virus A38L gene product is a 33-kDa integral membrane glycoprotein

The vaccinia virus gene A38L encodes a highly hydrophobic protein with amino acid similarity to mammalian integrin-associated protein (IAP). In this report we have identified the A38L protein of strain Western Reserve (WR), defined its membrane topology, and analyzed its role in virus production and virulence. An antiserum raised against an A38L peptide identified the A38L gene product as a 33-kDa protein which is expressed at low levels during virus infection. A serum from a rabbit previously infected with WR virus recognized the A38L protein, thus confirming that the A38L gene is expressed in vivo. Using a coupled in vitro-translation/membrane-translocation system the 33-kDa protein was shown to be a membrane-associated and glycosylated form of a 29-kDa polypeptide precursor. The membrane topology of the A38L protein was defined by its glycosylation and protease sensitivity when associated with microsomal membranes. The N-terminal immunoglobulin-like variable domain was protected from exogenous protease and was therefore in the lumen of the vesicle, whereas the C-terminus was sensitive and therefore cytoplasmic. A38L deletion and revertant viruses were constructed and were used to study the involvement of A38L in virus assembly, release, and virulence. Deletion of the A38L gene caused a slight reduction in virus plaque size but did not affect the production of intracellular mature virus or extracellular enveloped virus particles in tissue culture cells nor the virulence of the virus in the murine intranasal model. The A38L protein therefore possesses similar sequence and membrane topology to the mammalian IAP protein but is not required for virus particle production or virulence.

Cytokine receptors encoded by poxviruses: a lesson in cytokine biology

Poxviruses encode soluble versions of cytokine receptors, which are secreted from the infected cell to block the activity of the cognate cytokine. These viruses offer a unique model system to study the contribution of cytokines to the host response against infection. As discussed here by Antonio Alcamí and Geoffrey Smith, characterization of poxvirus proteins that counteract the immune response may lead to the identification of novel cytokines or cytokine receptors, as well as novel strategies to modulate the inflammatory response.

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Vaccinia virus serpins B13R and B22R do not inhibit antigen presentation to class I-restricted cytotoxic T lymphocytes

Vaccinia virus (VV) inhibits the presentation of certain epitopes from influenza virus nucleoprotein (NP), haemagglutinin (HA) and non-structural 1 (NS1) proteins to CD8+ cytotoxic T lymphocytes (CTL) by an unknown mechanism. We have investigated whether VV genes B13R and B22R, which encode proteins with amino acid similarity to serine protease inhibitors (serpins), are involved in this process. Recombinant VVs were constructed which express influenza virus proteins HA, NP or NS1 and which lack serpin gene B13R or both B13R and B22R. The lysis of cells infected with these viruses by influenza virus-specific CD8+ CTL was compared to the lysis of cells infected with viruses expressing both the influenza proteins and the serpin genes. Cytotoxicity assays showed that deletion of the VV serpin genes B13R and B22R and other genes between B13R and B24R did not increase the level of lysis, indicating that these genes are not involved in inhibition of antigen presentation of the epitopes tested.

Vaccinia, cowpox, and camelpox viruses encode soluble gamma interferon receptors with novel broad species specificity

Soluble receptors for gamma interferon (IFN-gamma) are secreted from cells infected by 17 orthopoxviruses, including vaccinia, cowpox, rabbitpox, buffalopox, elephantpox, and camelpox viruses, representing three species (vaccinia, cowpox, and campelpox viruses). The B8R open reading frame of vaccinia virus strain Western Reserve, which has sequence similarity to the extracellular binding domain of cellular IFN-gamma receptors (IFN-gamma Rs), is shown to encode an IFN-gamma binding activity by expression in recombinant baculovirus. The soluble virus IFN-gamma Rs bind IFN-gamma and, by preventing its interaction with the cellular receptor, interfere with the antiviral effects induced by this cytokine. Interestingly, in contrast to cellular IFN-gamma Rs, which are highly species specific, the vaccinia, cowpox, and camelpox virus IFN-gamma Rs bind and inhibit the biological activity of human, bovine, and rat IFN-gamma but not mouse IFN-gamma. This unique broad species specificity of the IFN-gamma R would aid virus replication in different species and suggests that vaccinia, cowpox, and camelpox viruses may have evolved in several species, possibly including humans but excluding mice. Last, the conservation of an IFN-gamma R in orthopoxviruses emphasizes the importance of IFN-gamma in defense against poxvirus infections.

Comparison of periodontal disease in HIV seropositive subjects and controls (II). Microbiology, immunology and predictors of disease progression

The aims of this study were to compare the prevalence of suspected periodontal pathogens in subgingival plaque from 29 HIV seropositive and 27 control subjects and to determine the association of these bacteria with periodontal destruction. Subgingival plaque was collected from the mesiobuccal sites of all teeth, except 3rd molars. Bacteria were identified and enumerated using non-isotopic whole chromosomal DNA probes and a colony lift method. At baseline, HIV seropositive subjects had significantly higher mean % of Porphyromonas gingivalis than control subjects. This difference could be attributed to a subgroup of HIV seropositive subjects with widespread attachment loss. No correlations were observed between the mean %s of DNA probe species and mean attachment loss, CD4 and CD8 T lymphocyte counts or CD4: CD8 ratio. No significant microbiological differences were detected between active and control sites in HIV seropositive subjects on a longitudinal basis. There appeared to be an inverse relationship between the mean %s of P. gingivalis and V. parvula, with respect to progression of HIV infection. The ability of microbiological parameters to predict site-specific breakdown in HIV seropositive subjects requires further investigation.

Comparison of periodontal disease in HIV seropositive subjects and controls (I). Clinical features

The aims of this study were to investigate the prevalence and severity of periodontal diseases in HIV seropositive and assumed HIV seronegative individuals in the Edinburgh area. 29 HIV seropositive subjects were examined at baseline and at 3-monthly intervals. Attachment loss and dichotomous indicators of periodontal disease were recorded. 27 control subjects were seen at baseline only. Although there was no significant difference between the 2 groups in terms of mean attachment loss at baseline, HIV seropositive subjects had experienced more severe attachment loss localised to the lower incisor region. HIV seropositive subjects had a significantly higher mean % of sites exhibiting suppuration and redness. A distinct subgroup of 9 HIV seropositive subjects with widespread attachment loss was detected, which included those subjects with severely affected lower incisors. Site-specific attachment loss of > or = 3 mm was observed in only 20 sites out of 2814 sites in HIV+subjects observed longitudinally. The incidence of aggressive periodontal disease in this study was lower than anticipated, despite the inclusion of patients with advanced HIV infection or AIDS.

Vaccinia virus encodes a soluble type I interferon receptor of novel structure and broad species specificity

Vaccinia virus (VV) and other orthopoxviruses express a soluble type I interferon (IFN) receptor that for VV strain Western Reserve is encoded by gene B18R. The 60-65 kDa glycoprotein is related to the interleukin-1 receptors and is a member of the immunoglobulin superfamily, unlike other type I IFN receptors, which belong to the class II cytokine receptor family. The receptor has high affinity (KD, 174 pM) for human IFN alpha and, unlike other type I IFN receptors, has broad species specificity, binding to human, rabbit, bovine, rat, and mouse type I IFNs. This may have aided VV replication in multiple host species during evolution. A VV B18R deletion mutant is attenuated in a murine intranasal model. This type I IFN receptor represents the fourth VV protein that interferes with IFN and the fourth soluble cytokine receptor expressed by poxviruses.

African swine fever virus gene j13L encodes a 25-27 kDa virion protein with variable numbers of amino acid repeats

The African swine fever virus (ASFV) j13L gene encodes a 177 amino acid protein (19.0 kDa) with a putative transmembrane domain between residues 32 and 52. There is a potential signal peptide cleavage site at residue 54 and several possible motifs for phosphorylation and myristylation. Rabbit antisera raised against a synthetic peptide from the C terminus of the j13L ORF identified proteins of 25-27 kDa in cells infected with a recombinant vaccinia virus expressing the j13L ORF, in ASFV-infected cells and in purified extracellular ASF virions. In ASFV-infected cells the j13L protein was expressed late during infection and exhibited size variation (25-27 kDa) between the different ASFV strains. Nucleotide sequence analysis of the gene in these strains showed that these size differences were due to variation in the number and sequence of tandemly repeated amino acid repeats. Although ASFV-infected animals made antibodies to the j13L protein, no protection was observed when pigs were vaccinated with a recombinant vaccinia virus expressing the j13L ORF.

Effects of creatine phosphate and inorganic phosphate on the sarcoplasmic reticulum of saponin-treated rat heart

1. Ventricular trabeculae from rat heart were permeabilized by treatment with saponin. In the presence of 150 nM Ca2+, application of 20 mM caffeine released Ca2+ from the sarcoplasmic reticulum (SR), resulting in a transient contracture. Ca2+ released from the SR was detected using fura-2 fluorescence. The amplitudes of the caffeine-induced Ca2+ transients were used to assess SR Ca2+ content. 2. In the absence of creatine phosphate (CP), introduction of 5-30 mM inorganic phosphate (Pi) caused a net release of Ca2+ from the SR. Subsequent caffeine-induced Ca2+ and tension transients were smaller in the presence of Pi. Under these conditions, 30 mM Pi decreased the caffeine-induced Ca2+ transients by 45 +/- 3.1% (mean +/- S.D., n = 14). On removal of Pi, the [Ca2+] transiently decreased and the caffeine-induced Ca2+ transients returned to control levels over 4-6 min. 3. In the presence of CP (5-15 mM), the Ca2+ transients were unaffected by the introduction of Pi (5-30 mM) or slightly increased in amplitude. Pi (30 mM) significantly increased the caffeine-induced Ca2+ transients by 7 +/- 8.8% (mean +/- S.D., n = 19, P < 0.05) in the presence of 15 mM CP. The release of Ca2+ on addition of Pi and decrease in [Ca2+] on Pi withdrawal was less pronounced or absent completely in the presence of CP. The inhibitory effects of Pi on caffeine-induced Ca2+ release became apparent as the [CP] was decreased from 5 to 0 mM. 4. In the presence of the creatine phosphokinase inhibitor dinitro-fluorobenzene (DNFB) the effects of Pi (in the presence of CP) were qualitatively similar to the results obtained in the absence of CP, although the decrease in caffeine-induced Ca2+ release was less pronounced. 5. These results suggest that the rise in [Pi]i during ischaemia or anoxia will have little effect on the regulation of Ca2+ by the SR while the [CP]i remains above 5 mM. However, as the [CP] decreases below 5 mM, the accumulation of Pi within the cytosol will progressively reduce the SR Ca2+ content. CP may act in conjunction with endogenous creatine phosphokinase to modify the response of the SR to Pi, and possible mechanisms are considered.

Vaccinia virus serpins B13R (SPI-2) and B22R (SPI-1) encode M(r) 38.5 and 40K, intracellular polypeptides that do not affect virus virulence in a murine intranasal model

A characterization of genes B13R (SPI-2) and B22R (SPI-1) from vaccinia virus strain Western Reserve (WR) is presented. These genes are transcribed early during infection and the predicted encoded proteins show similarity to the superfamily of serine protease inhibitors (serpins). The 5' transcriptional initiation site of each gene was mapped by primer extension experiments to 71-72 and 31 nucleotides upstream of the B13R and B22R open reading frames (ORFs), respectively. Each ORF was expressed in Escherichia coli and specific antisera were raised against the protein produced. These antisera were used to identify the B13R- and B22R-encoded proteins in vaccinia virus-infected cells as stable, intracellular, nonglycosylated proteins of M(r) 38.5K and M(r) 40K, respectively. The B22R gene product was detected in all orthopoxviruses tested including cowpox, rabbitpox, and vaccinia strains WR, Copenhagen, Tashkent, Tian Tan, Lister, Wyeth, IHD-J, and IHD-W. In contrast, the B13R gene product had a more limited distribution and was not detected in Copenhagen, Tashkent, Lister, and Tian Tan. Viable virus deletion mutants that lacked only B13R or B22R coding sequences (delta B13R and delta B22R) and revertant viruses in which the deleted gene was restored were constructed by transient dominant selection. The growth of the deletion mutants in cell culture was indistinguishable from that of wild-type virus. Additionally the virulence of each deletion mutant was indistinguishable from wild-type and revertant viruses in a murine intranasal model.

Effects of oxidants on the sarcoplasmic reticulum of saponin treated rat ventricular trabeculae

OBJECTIVE

The aim was to determine the effects of the superoxide anion, hydrogen peroxide, and hypochlorous acid on in situ cardiac sarcoplasmic reticulum.

METHODS

Simultaneous measurement of caffeine induced calcium release from the sarcoplasmic reticulum and subsequent myofilament tension generation was made on saponin permeabilised rat ventricular trabeculae before, during, and after exposure to various reactive oxygen species. The superoxide anion (O2.-) was generated using the xanthine-xanthine oxidase system, hypochlorous acid (HOCl) was prepared from NaOCl, and hydrogen peroxide (H2O2) was added from a 30% stock solution.

RESULTS

At [O2.-] sufficient to abolish tension generation by the myofilaments completely, the associated caffeine induced calcium release was unaffected. Both H2O2 and HOCl diminished caffeine induced calcium release but had differential effects on the associated tension response. Exposure to HOCl favoured the occurrence of spontaneous calcium releases from the sarcoplasmic reticulum.

CONCLUSIONS

The reactive oxygen species H2O2 and HOCl reduced the amount of calcium release from the sarcoplasmic reticulum while O2.- was without effect. In some preparations it was observed that HOCl favoured spontaneous calcium release which might additionally reduce the calcium content of the sarcoplasmic reticulum.

Effects of time response on the point spread function of a scanning radiometer

Scanning radiometers on satellites have a finite response time, because of the detector and the associated electronics. The radiometer measurement as it scans over a point source of radiation of unit strength is the point spread function (PSF). The time response causes a widening and skewing of the PSF. The PSF of a scanning radiometer that has well-focused optics together with time responses for the detector and electronic filter is treated in the time domain. The PSF can be expressed in terms of the system time response to a step input. For a first-order system time response, the displacement of the centroid is the product of the system time constant and the scan rate of the radiometer. The electronic filter further displaces the centroid of the PSF by the product of the scan rate and the filter time constant. Also, the width of the PSF in the scan direction will be increased because of the system time response. The minimum resolvable feature is of the order of the width of the PSF, thus the system time response limits the resolution in the scan direction that can be obtained. The analysis is illustrated by applying it to the Clouds and Earth Radiant Energy System experiment scanning radiometer.

Diagnosis of periodontal disease activity by detection of key microbial antigens

This paper reviews the development of various rapid microbial identification techniques and their potential rôle in the diagnosis of active periodontal tissue destruction. It also explores the concerns expressed by some, that although these techniques offer enormous promise as research tools, validation and translation of test results to clinical diagnosis, prognosis and treatment planning are still problematic. It may be premature to recommend these tests to clinicians in practice. Further longitudinal studies are required to establish the best use of these techniques in a clinical setting.

Vaccinia virus gene A36R encodes a M(r) 43-50 K protein on the surface of extracellular enveloped virus

A characterization of vaccinia virus strain Western Reserve (WR) open reading frame (ORF) A36R is described. This ORF is predicted to encode a 221-amino-acid protein (M(r) 25.1 K) with an amino-terminal hydrophobic sequence, seven potential sites for attachment of N-linked carbohydrate, but no carboxy-terminal transmembrane anchor. It is identical in vaccinia strain Copenhagen and shares 94.6% amino acid identity with the corresponding ORF in variola virus strains Harvey, India-1967, and Bangladesh-1975. RNA analyses detected a 600-nucleotide, early transcript that initiated 10-13 nucleotides upstream of the A36R ORF, and heterogeneously sized late transcripts running across the ORF. A rabbit antiserum raised against an Escherichia coli glutathione S-transferase fusion protein identified M(r) 43-50 K proteins that accumulated late during vaccinia virus infection and fractionated as integral membrane proteins during Triton X-114 partitioning. Similar polypeptides were expressed by vaccinia virus strains Tian Tan, Tashkent, Lister, Wyeth, Copenhagen, and IHD-J and by rabbitpox virus and cowpox virus (strain Brighton Red). Immunoblot analysis of purified and protease-digested intracellular mature virus (IMV) and extracellular enveloped virus (EEV) showed that the A36R proteins were present on the surface of EEV with type II membrane topology, but were absent from IMV. A WR deletion mutant lacking the A36R ORF (delta A36R) had a small plaque phenotype on all cell lines tested. IMV formation by delta A36R was unaltered but EEV formation was reduced approximately fivefold compared to wild-type (WT) when measured either by density gradient analysis of isotopically labeled virions or by infectivity assays. Thus the loss of the A36R protein from the EEV surface did not reduce EEV specific infectivity in vitro. Despite this, delta A36R showed striking attenuation compared with WT in a murine intranasal model. Finally, a revertant virus in which the A36R ORF was restored showed WT plaque size, EEV formation, and virulence, demonstrating that all the phenotypic differences of delta A36R were attributable to loss of the A36R gene and not to other mutations acquired during its construction.

Deletion of fowlpox virus homologues of vaccinia virus genes between the 3 beta-hydroxysteroid dehydrogenase (A44L) and DNA ligase (A50R) genes

A fragment of 4156 bp of fowlpox virus (FPV) genomic DNA contains homologues of vaccinia virus 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4 isomerase (3 beta-HSD; A44L) and DNA ligase (A50R) genes. The FPV locus has clearly been rearranged relative to that of vaccinia virus as homologues of genes A45R to A49R, including the thymidylate kinase and a gene with homology to superoxide dismutase, are deleted. The deleted genes are replaced by two open reading frames: for a serine proteinase inhibitor with homology to vaccinia virus gene K2L and for a protein with no significant homology to proteins in the databases. In addition, the FPV homologues of A44L and A50R are in the same polarity in FPV whereas they are in opposite polarities in vaccinia virus. Increased 3 beta-HSD activity has been demonstrated in cells infected with either of two different strains of FPV or with canarypox virus.

Effect of altered bathing pH on calcium activated force in alpha toxin permeabilised rat portal vein and human umbilical artery

OBJECTIVE

The aim was to investigate the effect of altered bathing pH on calcium activated force generated by the contractile proteins in an alpha toxin permeabilised phasic (rat portal vein) and tonic (human umbilical artery) smooth muscle.

METHODS

Strips of the two muscles were permeabilised using crude alpha toxin from Staphylococcus aureus (2 mg.ml-1). The relationship between [Ca2+] and tension was then examined at different bathing pH values. [Ca2+] was monitored using indo-1 fluorescence.

RESULTS

GTP-gamma-S (100 microM) potentiated maximum calcium activated force in rat portal vein on average to 146%, but had no significant effect on human umbilical artery, confirming the difference in contractile behaviour between the two muscles. Lowering bathing pH from 7.2 to 6.7 depressed submaximal calcium activated force and increased maximum calcium activated force in rat portal vein. Raising bathing pH from 7.2 to 7.7 depressed both submaximal and maximum calcium activated force in rat portal vein. Altered bathing pH had no significant effect on either maximum or submaximal calcium activated force in human umbilical artery. The calcium sensitivity of tension production was not significantly effected by acidic pH in either preparation. However, alkaline pH caused a similar fall in the calcium sensitivity in both preparations.

CONCLUSIONS

Tension generated from the contractile proteins of a phasic smooth muscle (rat portal vein) are more sensitive to altered bathing pH than those of a tonic smooth muscle (human umbilical artery).

Effects of pH and inorganic phosphate on rigor tension in chemically skinned rat ventricular trabeculae

1. Ventricular trabeculae from rat heart were chemically skinned with Triton X-100, which disrupts all cellular membranes including the sarcoplasmic reticulum. In the effective absence of Ca2+ (10(-9) M), trabeculae developed a maintained rigor contracture when ATP was withdrawn from the bathing solution. 2. The final level of tension obtained following withdrawal of ATP was dependent upon the pH of the bathing solution during development of rigor. Rigor tension at pH 5.5 was 10.1 +/- 0.9% (n = 8, mean +/- S.E.M.) of that at pH 7.0. Bathing the preparation in alkaline solution increased rigor force. At pH 8.0, rigor force increased to 218 +/- 6.7% (n = 4) of control responses developed at pH 7.0. The rate of development of rigor tension increased as the pH of the bathing solution was increased. Once established, rigor tension was unaffected by subsequent changes in pH. These effects of pH were fully reversible within the range 5.5-8.0. 3. The final level of rigor tension was slightly reduced when inorganic phosphate (P(i)) was included in the bathing solution prior to withdrawal of ATP. P(i) concentrations of 10, 20 and 30 mM reduced rigor tension to 87 +/- 2, 83 +/- 3 and 82 +/- 4% respectively. There was no significant effect of P(i) on the rate of development of rigor. The effect of P(i) at pH 6.0 was not significantly different from that observed at the control pH of 7.0. 4. These results suggest that the fall of intracellular pH and, to a lesser extent, the rise in [P(i)] that occurs during ischaemia will partially inhibit the development of a rigor contracture.

Nucleotide sequence of a 55 kbp region from the right end of the genome of a pathogenic African swine fever virus isolate (Malawi LIL20/1)

The nucleotide sequence of a 55098 bp region from the right end of the genome of a virulent African swine fever virus (ASFV) isolate (Malawi LIL20/1) has been determined. Translation of the sequence identified 67 major open reading frames (ORFs) which are closely spaced and read from both DNA strands. At six positions intergenic tandem repeat arrays are found. Comparison of the predicted amino acid sequences of encoded proteins with protein sequence databases identified a number of homologies. These include three subunits of RNA polymerase, a protein with homology to transcription factor SII (TFSII), a DNA ligase, two subunits of mRNA capping enzyme, a DNA topoisomerase type II, a dUTPase, a protein kinase, three helicases, a ubiquitin-conjugating enzyme, a protein with homology to the nif S and nif S-like proteins identified in some bacteria and Saccharomyces cerevisiae, a protein with homology to both a myeloid differentiation primary response antigen (MyD116) and to a herpes simplex virus-encoded neurovirulence-associated protein (ICP34.5), a protein with homology to the ASFV-encoded structural protein p22, two proteins with homology to copies of the ASFV-encoded multigene family 360 and one protein with homology to the ASFV-encoded multigene family 110. Four genes encode proteins which have homology to each other and constitute a new multigene family (MGF100). Nine ORFs encode proteins which contain predicted transmembrane domains. The possible functions of these predicted ASFV-encoded proteins are discussed and the evolutionary relationship of ASFV to other viruses are considered. Despite the similarities in genome structure and replication strategy of ASFV with poxviruses, sequence similarity between them is low and the organization of ASFV-encoded genes is not colinear with that of the orthopoxviruses.

Vaccinia virus core protein VP8 is required for virus infectivity, but not for core protein processing or for INV and EEV formation

A recombinant vaccinia virus, vDW4, has been constructed in which the L4R gene encoding the VP8 core DNA-binding protein is inducibly regulated by IPTG (isopropyl beta-D-thiogalactopyranoside). This virus produced normal-sized plaques in the presence of IPTG, but tiny plaques in the absence of inducer. Production of infectious progeny virus was reduced by 97% when VP8 synthesis was repressed and immature virions which had defective interactions between the granular viroplasm and the surrounding virion membrane were evident. However, despite the formation of these abnormal immature virions, virus maturation was able to proceed with the production of mature intracellular naked virus and extracellular enveloped virus particles of normal density. These mature particles were produced to approximately 80% of wild-type levels, but were around 100-fold less infectious. Consistent with the formation of mature virions, the repression of VP8 synthesis did not inhibit proteolytic processing of the major core proteins p4a and p4b. These results suggest that VP8 is required for correct association of the viroplasm and the immature virion envelope and that VP8 must be present during virus assembly for the production of fully infectious progeny virus.

The regulation of membrane 125I- and 86Rb+ permeability in a virally transformed cell line (NCL-SG3) derived from the human sweat gland epithelium

We have explored the factors that may regulate membrane permeability in a cell line (NCL-SG3) derived from the human sweat gland epithelium. Ionomycin increased the rate of 125I-efflux from preloaded cells and this action appeared to be due to an increase in intracellular free calcium ([Ca2+]i). The ionomycin-evoked increase in 125I- efflux was reduced in cells that were exposed either to barium or to valinomycin in the presence of a high concentration of external potassium. It thus appears that a fraction of the ionomycin-evoked increase in 125I- efflux is due to the activation of potassium channels and experiments using 86Rb+ also suggested that ionomycin increased the rate of potassium efflux, an effect which was totally abolished by barium. Blockade of Na(+)-K(+)-2Cl- cotransport and of Cl- -HCO3- exchange reduced the basal rate of 125I- efflux and the ionomycin-evoked increase in 125I-efflux from control cells and from cells depolarized by valinomycin. These transport systems thus contribute to anion efflux, although [Ca2+]i-dependent chloride channels also appear to be present. Acetylcholine increases [Ca2+]i in the secretory cells of human sweat glands, but this neurotransmitter did not increase [Ca2+]i in NCL-SG3 cells and so membrane permeability was not under cholinergic control. Adrenaline did not increase [Ca2+]i, but this hormone did evoke cyclic-3',5'-adenosine monophosphate (cyclic AMP) production. However, membrane permeability was not under adrenergic control, as the cells did not appear to express functional, cyclic AMP-dependent anion channels. This may be because they were not fully differentiated under the culture conditions. ATP consistently evoked a dose-dependent increase in anion efflux that appeared to be mediated by [Ca2+]i. The increase in [Ca2+]i was initiated by the release of calcium from a limited internal store and was subsequently sustained by calcium influx. UTP and ADP also increased [Ca2+]i, whereas adenosine, AMP and alpha,beta-methylene ATP were without effect. These data thus suggest that a subclass of type 2 purine receptor, which is functionally coupled to phosphoinositidase C, is present in these cells.

Virus strategies for evasion of the host response to infection

The attack on viruses and virus-infected cells by the mammalian immune system has provided considerable selective pressure for viruses that have evolved vigorous countermeasures to pre-empt, neutralize or evade this host attack. These countermeasures are astonishingly diverse, and their study imparts fundamental information about immunology and the mechanisms enabling viruses to survive and cause disease.

The metabolic consequences of an increase in the frequency of stimulation in isolated ferret hearts

1. The metabolic consequences of an increase in the frequency of stimulation were examined in isolated ferret hearts. Intracellular pH (pHi) and the intracellular concentrations of phosphocreatine ([PCr]i), inorganic phosphate ([Pi]i) and ATP were measured by 31P nuclear magnetic resonance (NMR) spectroscopy. 2. Increasing the stimulus rate from 0.1-0.7 to 2 Hz caused an increase in [Pi]i and a decrease recovery of both [PCr]i and [Pi]i during continued stimulation. There was no change in [ATP]i during stimulation at 2 Hz. Increasing the stimulus rate caused an intracellular acidosis of around 0.1 pH units. 3. Increasing the stimulus rate generally caused an initial increase in developed pressure, followed by a decrease over 1-2 min to a steady level slightly lower than developed pressure at the low (control) stimulus rate. The increase in stimulus rate caused a 4- to 6-fold increase in time-averaged muscle activity. 4. Both oxygen uptake and production of lactate increased on 2 Hz stimulation. Lactate production accounted for less than 5% of ATP production at low or high stimulus rates, suggesting that significant anoxia was not occurring during stimulation. The observed lactate production was, however, sufficient to explain most of the intracellular acidosis observed when the stimulus rate was raised. When glycolysis was prevented by removal of glucose and depletion of glycogen stores, 2 Hz stimulation was accompanied by an intracellular alkalosis rather than an acidosis, suggesting that lactate production by glycolysis was the cause of the intracellular acidosis. 5. Reducing the rate of glycolysis increased the size of changes in [PCr]i and [Pi]i evoked by stimulation at 2 Hz. Furthermore, there was now no partial reversal of the changes in [PCr]i and [Pi]i during 2 Hz stimulation. 6. When oxidative phosphorylation was inhibited by replacing O2 with N2, increasing the rate of stimulation from 0.1-0.7 to 1-2 Hz caused an initial increase followed by a large fall in developed pressure, which declined to a level well below that at the control stimulus rate. The increase in stimulus rate was accompanied by a large fall in [PCr]i, an increase in [Pi]i, and an intracellular acidosis of 0.1-0.3 pH units. The fall in developed pressure was consistent with the known effects of the rise in [Pi]i and the fall in pHi on the contractile apparatus.

Relationship between intracellular pH and metabolite concentrations during metabolic inhibition in isolated ferret heart

1. Intracellular pH (pHi) and phosphorus metabolites were measured in isolated ferret hearts with 31P nuclear magnetic resonance (NMR). 2. The application of cyanide (to mimic hypoxia) produced a fall of the concentration of phosphocreatine ([PCr]) and a rise of those of inorganic phosphate ([Pi]) and sugar phosphates. These were accompanied by an intracellular acidosis. 3. If glycolysis was partly inhibited by prior exposure to a glucose-free solution then the application of cyanide also produced a fall of [ATP]. The acidosis was similar to that observed in the presence of glucose. 4. If glycolysis was completely inhibited by iodoacetate then the acidosis produced by subsequent addition of cyanide developed more quickly. 5. The results are reproduced by a model which incorporates lactic acid production as well as the effects of protons released and absorbed by the changes in metabolite concentrations. The results suggest that the acidosis produced by cyanide (without inhibition of glycolysis) is largely due to lactic acid production. When glycolysis is partly inhibited (glucose-free solution) the acidosis produced by cyanide is partly due to protons released by ATP breakdown. Finally, when glycolysis is entirely inhibited the acidosis is completely due to ATP breakdown. There is no need to postulate a contribution on this time scale from inhibition of pH regulating mechanisms.

Characterization of vaccinia virus gene B12R

We report the characterization of vaccinia virus gene B12R which is predicted to encode a 33K protein with 36% amino acid identity to the serine/threonine protein kinase encoded by vaccinia virus gene B1R. S1 nuclease protection experiments showed that gene B12R is transcribed early during infection from an initiation site 11 bp upstream of the open reading frame (ORF). The gene encodes a 33K polypeptide that is not required for virus replication in tissue culture nor for virus virulence in a murine intranasal model. Expression of the B12R gene in Escherichia coli produced an abundant 33K polypeptide which lacked protein kinase activity under conditions in which the protein kinases encoded by vaccinia virus gene B1R and African swine fever virus gene j9L are active.

Simultaneous hybridization and subsequent colour detection of subgingival bacterial DNA on colony lifts

This paper reports the development of a protocol allowing hybridization and detection of DNA fixed to nylon colony lifts from up to three species of bacteria simultaneously. Half ml samples of serial dilutions of pure cooked-meat broth (CMB) cultures of Capnocytophaga ochracea, Actinobacillus actinomycetemcomitans and Prevotella intermedia were grown on trypticase soy blood agar (TSBA) plates for 7 days in an anaerobic chamber. From the same CMBs a further set of dilutions was completed that contained all three species. Samples from these dilutions produced mixed-growth TSBA plates following anaerobic incubation for 7 days. After incubation, colony counts on pure-growth TSBA plates were enumerated by colony counter. Colony counts of C. ochracea, A. actinomycetemcomitans and P. intermedia on mixed-growth TSBA plates were enumerated by nylon colony lift, simultaneous hybridization with non-isotopic whole chromosomal DNA probes and alkaline phosphatase substrates generating three colours. The results indicate that the protocol correctly identified and differentiated between the three species on mixed-growth TSBA plates. The proportions of each species and mean total colony count expected by counting pure plates were in agreement with the proportions of each species and total colony counts enumerated by DNA probes on mixed growth plates. The development of simultaneous hybridization and multicolour detection will result in improved data recovery from dental plaque samples, in addition to reducing the cost and labour required in current colony-lift protocols, without affecting the specificity or sensitivity of the probes used.

Effects of 2,3-butanedione monoxime on sarcoplasmic reticulum of saponin-treated rat cardiac muscle

We have studied the effects of 2,3-butanedione monoxime (BDM) on the sarcoplasmic reticulum (SR) of saponin-treated rat cardiac trabeculae. Rapid application of 20 mM caffeine released Ca2+ from the SR, which was detected using the fluorescent Ca2+ indicator indo 1. The amplitude of the caffeine-induced Ca2+ transient was used as an index of the Ca2+ content of the SR before, during, and after exposure to various concentrations of BDM. BDM (1-5 mM) had little effect on caffeine-induced Ca2+ release. At these levels of BDM, force was inhibited predominantly by a direct action of BDM on the myofilaments. However, with higher concentrations (5-30 mM), BDM caused a concentration-dependent decrease in the amount of Ca2+ released from the SR in response to caffeine. This action of BDM may contribute to the negative inotropic effect of the drug in intact cardiac preparations by reducing the amount of Ca2+ available for release during systole. Rapid application of BDM induced a net release of Ca2+ from the SR. Both BDM and caffeine-induced Ca2+ releases were abolished following treatment of the muscle with 10 microM ryanodine. BDM failed to release Ca2+ in the absence of ATP or after substitution of ATP with nonhydrolyzable adenine nucleotides. In contrast, caffeine released Ca2+ in the absence of ATP. The possible involvement of the Ca(2+)-uptake pump in the action of BDM on the SR is discussed.

Duplicated genes within the variable right end of the genome of a pathogenic isolate of African swine fever virus

The right variable region of the genome of a pathogenic strain of African swine fever virus (ASFV), Malawi LIL20/1, has been sequenced and 15 open reading frames (ORFs) identified by computer analysis. Eight of these ORFs were found to be similar to previously described ASFV ORFs and three of these belong to two previously described multiple gene families (MGF), 360 and 110. Four of the remaining five ORFs belong to a novel MGF, designated MGF 100, and the last ORF encodes a protein that is similar to the virus structural protein, p22. Copies of MGF 110 and the gene coding for p22 have previously been characterized only at the left end of the ASFV genome. The organization of these genes suggests evolution by duplications, deletions and sequence transposition from one end of the genome to the other. Sequence comparisons of members of MGF 360 suggest that the Malawi LIL20/1 genome has undergone separate DNA rearrangements compared to the Ba71V genome. Lastly, one ORF was found to be similar to the myeloid differentiation primary response protein, MyD116 and to the herpes simplex virus neurovirulence-associated factor ICP34.5.

Investigation of stimulus-secretion coupling in equine sweat gland epithelia using cell culture techniques

When sweat glands isolated from samples of horse skin were explanted and cultured under favourable conditions, they could exhibit cellular outgrowth. This growth could be maintained for 2–4 weeks and these primary cultures were then disaggregated and the resultant cell suspensions used to initiate epithelial cell lines. Secretion from intact equine sweat glands is regulated by beta 2-adrenoceptors and appears to be mediated by cyclic AMP, but there is evidence that calcium may also play a role. Adrenaline could increase the cyclic AMP content of the cultured cells and this response was mediated by beta 2-adrenoceptors. Adrenaline was also able to evoke a small increase in intracellular free calcium ([Ca2+]i) but the pharmacology of this response remains obscure. Adrenaline thus activates at least two potentially important second-messenger signalling pathways which have the capacity to interact, because adrenaline-evoked cyclic AMP formation was inhibited if [Ca2+]i was raised with ionomycin. The chloride permeability of mammalian epithelial cells characteristically rises during secretion, and adrenaline could increase chloride permeability in the cultured epithelia but the cells did not contain cyclic-AMP-dependent chloride channels and so this response was mediated by [Ca2+]i.

The effects of lactic acid production on contraction and intracellular pH during hypoxia in cardiac muscle

During hypoxia cardiac contraction declines and there is an intracellular acidosis. We find that, if this acidosis is abolished by decreasing pCO2 there is little restoration of force. Therefore the acidosis is not the major cause of the decline of force. The acidosis may partly result from the generation of lactic acid. No acidosis, is however, seen in isolated cardiac cells. Furthermore a theoretical model shows that lactic acid production would be expected to produce a transient acidosis. We suggest that the observed maintained acidosis may be a consequence of extracellular lactic acid accumulation affecting intracellular pH.

Three African swine fever virus genes encoding proteins with homology to putative helicases of vaccinia virus

Sequence analysis of the SalI g, h, i and j restriction fragments of the African swine fever virus (ASFV) genome from the virulent isolate Malawi (LIL20/1) identified three open reading frames (ORFs) encoding predicted proteins of 125.0K (g10L), 80.4K (j10L) and 58.0K (j11L) which showed homology to members of the DNA and RNA helicase superfamily. ORFj10L was related to protein 4 of the Kluyveromyces lactis killer plasmid pKG12 and to two putative helicases, D6R and D11L, of vaccinia virus. ORF g10L was most closely related to ASFVj10L and to vaccinia virus D11L. ORFj11L was homologous to A18R, a third putative helicase of vaccinia virus. The possible functions of these genes in the replication of ASFV are discussed and the evolutionary implications are considered.

African swine fever virus encodes a serine protein kinase which is packaged into virions

Nucleotide sequencing of the SalI j region of the virulent Malawi (LIL20/1) strain of African swine fever virus (ASFV) identified an open reading frame (ORF), designated j9L, with extensive similarity to the family of protein kinases. This ORF encodes a 35.1-kDa protein of 299 amino acids which shares 24.6% amino acid identity with the human pim-1 proto-oncogene and 21.0% identity with the vaccinia virus B1R-encoded protein kinase. The ASFV ORF contains the motifs characteristic of serine-threonine protein kinases, with the exception of the presumed ATP-binding site, which is poorly conserved. The ORF was expressed to high levels in Escherichia coli, and the recombinant enzyme phosphorylated a calf thymus histone protein on serine residues in vitro. An antibody raised to an amino-terminal peptide of the ASFV protein kinase was reactive with the recombinant protein in Western immunoblot analyses and was used to demonstrate the presence of the protein kinase in ASF virions.

The vaccinia virus 42-kDa envelope protein is required for the envelopment and egress of extracellular virus and for virus virulence

Vaccinia virus gene B5R encodes a M(r) 42K glycoprotein that is expressed throughout infection and forms part of the envelope of extracellular virus. In this paper deletion mutants (delta B5R) lacking the B5R open reading frame (ORF) from the Western Reserve (WR) and IHD-J strains of vaccinia virus have been constructed and shown to form very small plaques compared with the wild-type viruses. This phenotype was directly attributable to loss of the B5R gene since re-insertion of this gene from WR or IHD-J into the WR mutant lacking B5R (W-delta B5R) restored a normal plaque phenotype. In the latter case the failure of the revertant to form comets indicated that the nine amino acid differences in the B5R ORF between the IHD-J and WR strains of virus are not responsible for comet formation by IHD-J virus. Furthermore, the B5R deletion mutant of IHD-J (I-delta B5R) still formed small comets. Despite the small plaque phenotype of the deletion mutants, normal yields of intracellular naked virus (INV) were produced. In contrast, deletion of B5R had a profound affect on the formation of the extracellular enveloped virus (EEV). Transmission electron microscopy indicated that INV particles were not wrapped by a double layer of Golgi-derived membrane and enveloped particles were not detected within the cell or on the cell surface without expression of the B5R protein. Biochemical measurement of EEV formation, by labeling infected cells with [3H]thymidine followed by cesium chloride density gradient centrifugation of particles released from the cells 24 hr postinfection, showed that only 10% of WT levels of EEV were produced by I-delta B5R. The loss of the B5R ORF caused severe attenuation in intranasally infected mice. At doses between 10(4) and 3 x 10(7) plaque-forming units there were no signs of disease in animals infected with W-delta B5R, whereas at comparable doses the WR parent virus caused significant mortalities. Finally, an ORF with 93.4% amino acid identity to vaccinia WR B5R is present in variola major virus strain Harvey and the B5R protein was shown by Western blotting to be expressed by all orthopoxviruses tested.

Thromboxane A2 analogue, U-46619, potentiates calcium-activated force in human umbilical artery

It has previously been shown that human umbilical artery (HUA) smooth muscle produces thromboxane A2 in response to increasing oxygen levels and that this thromboxane promotes contraction. To investigate the intracellular action of thromboxane A2, strips of HUA longitudinal smooth muscle were permeabilized using alpha-toxin from the bacterium Staphylococcus aureus. This treatment rendered the surface membrane permeable to low-molecular-weight substances but left functional thromboxane A2 receptors. Tension measurements were used to investigate the effect of the stable thromboxane A2 analogue, U-46619, on the Ca2+ sensitivity of smooth muscle contractile proteins. U-46619 (1 nM to 1 microM) potentiated submaximal Ca(2+)-activated force (generated by [Ca2+], 50 nM to 3 microM) but not maximal Ca(2+)-activated force (generated by [Ca2+], 10-100 microM). The specific thromboxane A2 receptor antagonist, GR-32191B (1 microM), inhibited the action of U-46619 (0.1 microM). The potentiation of submaximal Ca(2+)-activated force produced by the muscle in response to U-46619 (0.1 microM) was antagonized by guanosine 5'-O-(2-thiodiphosphate) (1 mM), the nonhydrolyzable analogue of GDP, and mimicked by guanosine 5'-O-(3-thiotriphosphate) (100 microM), the nonhydrolyzable analogue of GTP. These results suggest that U-46619 acts via the previously identified thromboxane A2 receptor to promote Ca2+ sensitivity of tension production in HUA smooth muscle. Furthermore, this effect appears to be mediated via a G protein.

Effects of pH and inorganic phosphate on force production in alpha-toxin-permeabilized isolated rat uterine smooth muscle

1. Strips of longitudinal smooth muscle isolated from rat uterus were permeabilized using crude alpha-toxin from the bacterium Staphylococcus aureus. This treatment rendered the surface membrane permeable to small molecular weight substances. Simultaneous measurements of tension and calcium concentration ([Ca2+]) (using indo-1 fluorescence) were used to investigate the effects of pH and inorganic phosphate concentration ([Pi]) on Ca(2+)-activated force generated by the contractile proteins. 2. Raising the [Pi] from 1 to 11 mM at a pH of 7.2 depressed both maximal and submaximal Ca(2+)-activated force. This effect of Pi was concentration dependent having the majority of its effect by 6 mM. 3. Further experiments at a submaximal [Ca2+] showed that Ca(2+)-activated force was enhanced by raising [Pi] from 6 to 11 mM suggesting that Pi increased the Ca2+ sensitivity of tension production. Based on these results, calculations indicate that the apparent affinity constant of Ca2+ for the contractile proteins increased from 4 x 10(6) M-1 to 6 x 10(6) M-1 on raising [Pi] from 1 to 11 mM. 4. Lowering pH from 7.2 to 6.7 at a [Pi] of 1 mM potentiated Ca(2+)-activated force with a small depression in the apparent Ca2+ sensitivity of tension production. This effect of pH on maximum (100 microM Ca2+) and submaximum (0.3 microM Ca2+) Ca(2+)-activated force was observed over a range of acidic pHs (7.0-6.7). 5. Increasing pH from 7.2 to 7.7 at a [Pi] of 1 mM depressed Ca(2+)-activated force with no effect on Ca2+ sensitivity of tension production. 6. Spontaneous contractions in intact rat myometrium are abolished under hypoxic conditions. Under these same conditions intracellular [Pi] rises and pH falls. The results of this study suggest that taken individually neither the effect of a rise in [Pi] nor a fall in pH on Ca(2+)-activated force generated by the contractile proteins can account for the effect of hypoxia on spontaneous contractions.

Phosphorylation of ribosomal proteins by the vaccinia virus B1R protein kinase

Two proteins of the 40S ribosomal subunit were shown to be phosphorylated in vitro by a vaccinia virus-encoded serine/threonine protein kinase. These were identified by two-dimensional gel electrophoresis as ribosomal proteins Sa and S2 and were shown by phosphoamino acid analysis to both be phosphorylated on serine and threonine residues. The three phosphorylated forms of S2 produced by the B1R protein kinase in vitro matched the phosphorylated forms of S2 previously observed in cells infected with vaccinia virus. These data strongly suggest that this enzyme is responsible for the phosphorylation of S2 and Sa which occurs early during vaccinia virus infection.

Current classifications of HIV-associated periodontal diseases

The occurrence of unusual and severe forms of periodontal disease in HIV-infected individuals is well recognised. Several classification schemes have been proposed in an effort to associate periodontal deterioration with progressive stages of HIV infection and to determine aetiological factors in tissue destruction. No classification to date has proved entirely satisfactory. This paper reviews current classification schemes and suggests an alternative based upon the periodontal status of a cohort of HIV seropositive patients in Edinburgh. The proposed classification includes 'conventional', non-specific gingivitis and adult periodontitis such as occur in HIV seronegative individuals, but which may also be seen in seropositive subjects. However, conditions termed linear gingivitis and necrotising periodontitis may be pathognomonic for HIV infection. It is recommended that the term 'HIV-associated' be dropped in relation to periodontal disease.

Ca-EGTA affects the relationship between [Ca2+] and tension in alpha-toxin permeabilized rat anococcygeus smooth muscle

The relationship between calcium concentration ([Ca2+]) and force in smooth muscle can be studied by permeabilizing the sarcolemma and bathing the preparation in a mock intracellular solution. Normally [Ca2+] is set in these solutions using the Ca2+ chelator EGTA in the concentration range of 4-10 mM. This study shows that lowering total EGTA concentration ([EGTA]t) below 10 mM depresses Ca(2+)-activated force generated in 0.1 microM Ca2+. The observed threshold for the effect of EGTAt is 0.2 mM, and the effect is maximal at approximately 10 mM. BAPTA, another Ca2+ chelator, also produces this effect. Tension production in smooth muscle is controlled by acto-myosin interaction. This in turn is mediated by the relative activities of myosin light chain kinase (MLCK) and phosphatase (MLCP). Inhibiting MLCP with Microcystin LR (10 microM), an increase [EGTAt] from 0.2 mM to 10 mM still enhanced force. This suggests that EGTA promotes phosphorylation of myosin by the activation of MLCK and not by inhibition of MLCP.