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Biomedical subjects

R J Johnston

Publications and source records attributed to R J Johnston.

At least 19 recordsLinked to original sources
PubMed2000

Compartmental specificity of cellular membrane fusion encoded in SNARE proteins.

Membrane-enveloped vesicles travel among the compartments of the cytoplasm of eukaryotic cells, delivering their specific cargo to programmed locations by membrane fusion. The pairing of vesicle v-SNAREs (soluble N-ethylmaleimide-sensitive factor attachment protein receptors) with target membrane t-SNAREs has a central role in intracellular membrane fusion. We have tested all of the potential v-SNAREs encoded in the yeast genome for their capacity to trigger fusion by partnering with t-SNAREs that mark the Golgi, the vacuole and the plasma membrane. Here we find that, to a marked degree, the pattern of membrane flow in the cell is encoded and recapitulated by its isolated SNARE proteins, as predicted by the SNARE hypothesis.

Biological Transport↗
PubMed2000

Close is not enough: SNARE-dependent membrane fusion requires an active mechanism that transduces force to membrane anchors.

Is membrane fusion an essentially passive or an active process? It could be that fusion proteins simply need to pin two bilayers together long enough, and the bilayers could do the rest spontaneously. Or, it could be that the fusion proteins play an active role after pinning two bilayers, exerting force in the bilayer in one or another way to direct the fusion process. To distinguish these alternatives, we replaced one or both of the peptidic membrane anchors of exocytic vesicle (v)- and target membrane (t)-SNAREs (soluble N-ethylmaleimide-sensitive fusion protein [NSF] attachment protein [SNAP] receptor) with covalently attached lipids. Replacing either anchor with a phospholipid prevented fusion of liposomes by the isolated SNAREs, but still allowed assembly of trans-SNARE complexes docking vesicles. This result implies an active mechanism; if fusion occurred passively, simply holding the bilayers together long enough would have been sufficient. Studies using polyisoprenoid anchors ranging from 15-55 carbons and multiple phospholipid-containing anchors reveal distinct requirements for anchors of v- and t-SNAREs to function: v-SNAREs require anchors capable of spanning both leaflets, whereas t-SNAREs do not, so long as the anchor is sufficiently hydrophobic. These data, together with previous results showing fusion is inhibited as the length of the linker connecting the helical bundle-containing rod of the SNARE complex to the anchors is increased (McNew, J.A., T. Weber, D.M. Engelman, T.H. Sollner, and J.E. Rothman, 1999. Mol. Cell. 4:415-421), suggests a model in which one activity of the SNARE complex promoting fusion is to exert force on the anchors by pulling on the linkers. This motion would lead to the simultaneous inward movement of lipids from both bilayers, and in the case of the v-SNARE, from both leaflets.

Antigens, Surface↗
PubMed2000

SNAREpins are functionally resistant to disruption by NSF and alphaSNAP.

SNARE (SNAP [soluble NSF (N-ethylmaleimide-sensitive fusion protein) attachment protein] receptor) proteins are required for many fusion processes, and recent studies of isolated SNARE proteins reveal that they are inherently capable of fusing lipid bilayers. Cis-SNARE complexes (formed when vesicle SNAREs [v-SNAREs] and target membrane SNAREs [t-SNAREs] combine in the same membrane) are disrupted by the action of the abundant cytoplasmic ATPase NSF, which is necessary to maintain a supply of uncombined v- and t-SNAREs for fusion in cells. Fusion is mediated by these same SNARE proteins, forming trans-SNARE complexes between membranes. This raises an important question: why doesn't NSF disrupt these SNARE complexes as well, preventing fusion from occurring at all? Here, we report several lines of evidence that demonstrate that SNAREpins (trans-SNARE complexes) are in fact functionally resistant to NSF, and they become so at the moment they form and commit to fusion. This elegant design allows fusion to proceed locally in the face of an overall environment that massively favors SNARE disruption.

Adenosine Triphosphate↗
PubMed2000

Thromboembolic disease: comparison of combined CT pulmonary angiography and venography with bilateral leg sonography in 70 patients.

OBJECTIVE: The purpose of this study was to compare combined CT pulmonary angiography and venography with leg sonography for accuracy and relative efficacy in diagnosis of deep venous thrombosis from the popliteal vein to the common femoral vein. SUBJECTS AND METHODS: Seventy consecutive patients with clinically suspected pulmonary embolism underwent both combined CT pulmonary angiography and venography and bilateral leg sonography within 24 hr. CT venograms were analyzed independently in a blinded fashion for quality of venous opacification and patency by two observers. CT venography was compared with sonography for femoropopliteal vein thrombosis, and the final assessment based on multiple subjective and objective clinical and imaging criteria was recorded in three categories: 1, CT venography better than sonography; 2, CT venography equivalent to sonography; and 3, sonography better than CT venography. RESULTS: Sixty-eight patients (97%) had a satisfactory or good quality CT venography examination. Two CT venography studies had false-positive findings due to flow artifacts. Both CT venography and sonography had positive findings for deep venous thrombosis in five patients, and both had negative findings in 63 patients (100% sensitivity, 97% specificity, 100% negative predictive value, and 71% positive predictive value). CT venography was better and more efficacious than sonography (category 1) in 25 patients (36%). CT venography was equivalent to sonography (category 2) in 26 patients (37%), and sonography was better than CT venography (category 3) in 19 patients (27%). CONCLUSION: Compared with sonography, CT venography in addition to CT pulmonary angiography is a relatively accurate method for evaluation of femoropopliteal venous thrombosis. Combined CT pulmonary angiography and CT venography may be more efficacious than sonography or two separate examinations in selected patients.

Adult↗
PubMed1999

Clinical validity of helical CT being interpreted as negative for pulmonary embolism: implications for patient treatment.

OBJECTIVE: The purpose of our study was to assess the clinical usefulness of helical CT findings that are interpreted as negative for pulmonary embolism. MATERIALS AND METHODS: One hundred twenty-six patients underwent 132 helical CT examinations and 352 patients underwent ventilation-perfusion scanning for suspected acute pulmonary embolism over a 17-month period at a single institution. Findings from clinical follow-up at a minimum of 6 months were assessed, with a special focus on the presence of recurrent thromboembolism and mortality in 78 consecutive patients in whom helical CT findings were interpreted as negative for pulmonary embolism and anticoagulant therapy was not administered (group I). During the same 17-month period, 46 patients underwent ventilation-perfusion scanning that was interpreted as normal (group II), and 132 patients underwent ventilation-perfusion scanning that was interpreted as showing a very low to low probability for pulmonary embolism (group III). Patients in groups II and III did not undergo helical CT or pulmonary angiography and did not receive anticoagulant therapy. However, clinical follow-up was solicited. Patients from groups II and III were used as control subjects. RESULTS: Nine patients in group I died, one of whom was found to have a microscopic pulmonary embolism at autopsy. In group II, four patients died, none of whom were shown to have a missed or recurrent pulmonary embolism. Of the 18 patients in group III who died, three had a recurrent or missed pulmonary embolism (mean interval, 9 days), and two were found to have deep vein thrombosis on sonography of the leg (mean interval, 12 weeks). Negative predictive values for helical CT, normal lung scanning, and low-probability ventilation-perfusion scanning were 99%, 100%, and 96%, respectively (p = .299). CT provided either additional findings or an alternate diagnosis in 42 (53.8%) of the 78 patients in whom helical CT findings had been interpreted as negative for pulmonary embolism. CONCLUSION: A helical CT scan can be effectively used to rule out clinically significant pulmonary emboli and may prevent further investigation or unnecessary treatment of most patients.

Adult↗
PubMed1998

Pulmonary embolism: diagnosis with spiral CT and ventilation-perfusion scanning--correlation with pulmonary angiographic results or clinical outcome.

PURPOSE: To compare the accuracy of spiral computed tomography (CT) with that of ventilation-perfusion (V-P) scintigraphy in the diagnosis of pulmonary embolism (PE). MATERIALS AND METHODS: Fifty-four patients in whom indeterminate V-P scans or discordant clinical and scintigraphic results were obtained underwent both V-P scanning and contrast material-enhanced spiral CT. The reference standard was pulmonary angiographic results in 26 patients (group I) or clinical outcome in 28 (group II). RESULTS: Six (25%) of 24 group I patients had proved PE. The prospective sensitivity and specificity for segmental or subsegmental PE were 67% and 100%, respectively, and the positive and negative predictive values were 100% and 90%, respectively. In two group II patients, V-P scans had high probability for acute embolism, but spiral CT scans showed only chronic PE; in one patients, the V-P scan had low probability and the CT scan was positive for acute PE. An alternative CT diagnosis was established in four (31%) of 13 patients in whom a normal or low-probability V-P scan was obtained. Clinical outcome was consistent with spiral CT results in all cases. CONCLUSION: Spiral CT has greater accuracy and specificity than V-P scanning in patients with an unresolved diagnosis and may be useful as the primary screening technique for PE.

Acute Disease↗
PubMed1998

Cardiac angiosarcoma: an unusual presentation with cutaneous metastases.

Angiosarcoma is the most common primary malignant neoplasm of the heart. The incidence of metastatic disease is 66% to 89%; however, initial presentation with metastatic disease is rare. We report the case of a patient who presented initially with soft tissue and cutaneous metastases in the absence of cardiac symptoms.

Adult↗
PubMed1994

Version of the osteoarthritic knee.

Version of normal and osteoarthritic knees is evaluated by computed tomography in this study. Version of the knee is defined as the static rotation of the tibia with respect to the femur in full knee extension. It is measured as the difference between the transverse axes of the femoral condyles and tibia. The average knee version, or external rotation of the tibia with respect to the femur across the normal knee, was 0 degree. Version of the osteoarthritic knee was 5 degrees. Rotation of the tibia with respect to the femur across the extended osteoarthritic knee is a relationship that will affect the placement of components in total knee arthroplasty. This relationship should be addressed in alignment instrumentation and technique to avoid component malalignment in total knee arthroplasty.

Femur↗
PubMed1993

Short duration radiotherapy in stage I seminoma of the testis: preliminary results of a prospective study.

Ninety-four patients with Stage I seminoma of the testis, treated between November 1989 and December 1991, received short duration radiotherapy (2000 cGy in 8 fractions) to the para-aortic area only. The treatment was well tolerated and, after a median follow-up time of 34 months (minimum 15 months), no patient has relapsed in the abdomen. One patient developed an apparently solitary distant metastasis from a latent teratoma and is disease free after chemotherapy. This form of radiotherapy would appear to be well-tolerated with a low relapse rate. It offers the advantage of a simpler and shorter technique compared with conventional therapy and avoids the necessity of intensive surveillance to detect relapse.

Adult↗
PubMed1988

Type III congenital cystic adenomatoid malformation associated with elevated maternal serum alpha-fetoprotein.

Congenital cystic adenomatoid malformation Type III with fetal ascites was diagnosed in a 19-week fetus after finding an abnormally elevated maternal serum alpha-fetoprotein value during routine screening. This discovery led to early elective termination of pregnancy. Sonographic evaluation of the fetal thorax is recommended in all cases referred for ultrasound because of unexplained elevation of maternal serum alpha-fetoprotein.

Adult↗
PubMed1987

Phase II trial of rDNA alfa 2b interferon in patients with malignant carcinoid tumor.

Fourteen patients with malignant carcinoid tumors were treated with rDNA alfa 2b interferon by sc injection three times per week. Treatment was started at a dose of 2 milliunits/m2, with escalations to 3, 5, 7, and 10 milliunits/m2 at 2-week intervals depending on toxicity. No objective tumor regressions were seen, but five of 14 patients (36%) had 50% reduction in 24-hour 5-hydroxyindoleacetic acid excretion and six of nine (67%) with carcinoid syndrome had a good symptomatic response. Biochemical responses occurred during the first 8 weeks of treatment, and escalation of the dose of interferon did not increase the response rate. The rDNA alfa 2b interferon has activity in patients with the carcinoid syndrome and should be used at a low dose (2-3 milliunits/m2) until symptoms recur.

Adult↗
PubMed1985

The use of acridine orange staining and image analysis to detect bacteriuria.

Fifty urine samples from a variety of urological patients were analysed using the fluorochrome acridine orange in an automated system. The results were compared with standard colony counts. The method has a potential value in the detection of significant infection particularly in population studies.

Acridine Orange↗
PubMed1985

The screening of more than 2,000 schoolgirls for bacteriuria using an automated fluorescence microscopy system.

After initial evaluation of a manual fluorescence microscopy system on a variety of urines the method was automated and subsequently tested in a population survey of urinary tract infection in schoolgirls. This automated Bactoscan system allowed a rapid analysis of urine samples and with the introduction of modifications to the staining protocol it correctly eliminated 91% of samples as being not significantly infected.

Autoanalysis↗
PubMed1985

A survey of bacteriuria in 2,234 schoolgirls in a Scottish new town.

The prevalence of urinary tract infection in a modern Scottish town has been ascertained in female school children aged 5-12. In 2,234 girls the initial prevalence of urinary tract infection is 3.3%. In addition to the information on urinary tract infection the social and personal history was available including data on incontinence, enuresis and current antibiotic therapy. The necessity to have a system available which allows a cheap and rapid assessment of population surveys is made.

Adolescent↗
PubMed1980

Non-invasive magnetopneumographic estimation of lung dust loads and distribution in bituminous coal workers.

Magnetopneumography is a non-invasive technique for measuring the ferrimagnetic portion of retained dust in the lungs by means of its permanent magnetism. Magnetopneumography was used to measure the magnetic fraction of coal mine dust in 21 retired disabled bituminous coal miners and 14 active miners. Twenty rural subjects served as controls. The retired disabled miners had significantly higher levels of pulmonary ferrimagnetic mineral than the control subjects and most active miners (p < 0.001). Three of the active miners had significantly higher levels of ferrimagnetic mineral than did the other active miners and the control subjects (p < 0.005), yet could not be differentiated from other miners by work history or chest roentgenograms. This elevation could not be accounted for by sources other than coal mine dust. A pattern of central hilar concentration of ferrimagnetic mineral was noted in both retired and active miners. These results suggest that magnetopneumography is sufficiently sensitive to permit the non-invasive study of coal mine dust accumulation and distribution in the lung.

Adult↗