Sucrose transport into plasma membrane vesicles from tobacco leaves by H+ symport or counter exchange does not display a linear component.

Uptake of [14C]sucrose by plasma membrane vesicles from leaves of tobacco (Nicotiana tabacum L.) was measured after the imposition of an inwardly directed proton gradient (delta pH = 2) and an electrical gradient (delta psi = -68 mV, inside negative) across the vesicle membrane. The vesicles were isolated from a microsomal fraction by two-phase partitioning using media that contained 330 mM of either sorbitol or sucrose. Sucrose transport into vesicles isolated using the sorbitol-containing media showed the hallmarks of electrogenic H+-symport, as it was highly dependent on delta pH, could be increased three- to four-fold by delta psi, and was abolished by carbonylcyanide m-chlorophenylhydrazone (CCCP). Transport of [14C]sucrose into vesicles that were isolated using the sucrose-containing media apparently occurred by counter exchange. Its initial influx also depended on a low external pH, but it was insensitive to CCCP and hardly stimulated by delta psi. Both symport and counter exchange obeyed simple Michaelis-Menten kinetics. Transport that depends linearly on the external sucrose concentration could not be detected, indicating that the 'linear' component that has been observed in sucrose uptake by leaf tissues does not represent a transport route that is provided by the sucrose symporter. The potential role of H+/sucrose-symporters in phloem unloading is briefly discussed.

Interexamination variation of whole breast ultrasound.

The purpose of this study was to determine the interexamination agreement of ultrasound of the breasts. This includes the complete process of performing whole breast ultrasound and interpreting the dynamic scanning and the static images by one person. In a prospective study, 58 patients with a clinical indication for mammography underwent an ultrasound examination of both breasts by three independent sonographers. The sonographers had full knowledge of the physical and mammographic findings. Histology and 12 month follow-up were used as the reference standard. Interobserver variability for both mammography and breast ultrasound was measured using linearly weighted kappa statistics. Receiver operator characteristic curves were constructed to compare the diagnostic performance of the observers. The interexamination agreement for the score of the probability of malignancy after mammography was substantial (kappas ranged from 0.63 to 0.65). The interexamination agreement for the final score of the probability of malignancy after mammography and ultrasound examination was slightly better (kappas ranged from 0.72 to 0.75). The area under the receiver operating characteristic curves after mammography and ultrasound examination ranged from 0.97 to 0.98. Ultrasound examination of the whole breast shows a substantial interexamination agreement. Ultrasound examination of the breast adds consistency to mammography and physical examination.

Electrodiffusional uptake of organic cations by pea seed coats. Further evidence for poorly selective pores in the plasma membrane of seed coat parenchyma cells.

In developing seeds, the permeability of the plasma membrane of seed coat parenchyma cells is crucial for the supply of nutrients to the embryo. Here, we report characteristics of the transport of the organic cation choline and the basic amino acid L- histidine (His; cation at pH 5, electroneutral at pH 7) into isolated seed coats of pea (Pisum sativum). Supplied at sub-micromolar concentrations, choline(+) accumulated in the seed coat tissue 5.1 +/- 0.8-fold, His(+) 2.4 +/- 0.3-fold, and His(0) 1.3 +/- 0.2-fold. Taking into consideration that at pH 5 His influxes as a cation but effluxes as a neutral molecule, these accumulations are in reasonable agreement with (electro) diffusional uptake at the prevailing membrane potential of -55 +/- 3 mV. At a concentration of 100 mM, choline(+) and His(+), but not His(0), depolarized the membrane of the parenchyma cells and neither of the substrates was accumulated. At this concentration, the relative influx (the ratio of influx and external concentration, a measure for membrane permeability) of choline and His was approximately 10 micromol g(-1) fresh weight min(-1) M(-1), similar to that found for neutral amino acids, sucrose, glucose, and mannitol. At lower concentrations, the relative influx of choline(+) and His(+) increased because of increasingly more negative membrane potentials, giving rise to apparent saturation kinetics. It is suggested that transport of organic cations can proceed by a general, poorly selective pore in the plasma membrane of seed coat parenchyma cells. This pore is thought to be responsible for the unloading of a range of solutes that serve as nutrients for the embryo.

Patient and occupational dosimetry in double contrast barium enema examinations.

A new and relatively simple method is presented to distribute total dose-area product (DAP) over a number of projections that model exposure during double contrast barium enema (DCBE) examinations. In addition, hitherto unavailable entrance and effective doses to the physician performing the DCBE examination have been determined. DAP, fluoroscopy time, number of images as well as some patient data were collected for 150 DCBE examinations. For a subset of 50 examinations, the distribution of DAP over 12 hypothetical but representative projections was estimated by measuring the entrance dose in the centre of each of these projections during the complete procedure. Effective dose to the patient was obtained using DAP to effective dose conversion coefficients calculated for each of the 12 projections. Exposure of the worker was quantified by measuring the entrance dose at the forehead, neck, arms, right hand and legs. The sex-averaged effective dose to the patient per examination was 6.4+/-2.1 mSv (mean+/-SD; n=50) and the corresponding DAP was 44+/-22 Gy cm(2). The effective dose to the worker per examination was 0.52 microGy (n=50), whereas the highest entrance dose of 30+/-25 microGy was found for the right arm. The proposed method for deriving the distribution of total DAP over a set of representative projections is much less time consuming than visual observation of patient exposure, whilst accuracy seems acceptable. Entrance and effective doses per examination for workers in DCBE examinations are very low. For a normal workload, doses remain far below the legally established dose limits.

Proton-symport of L-valine in plasma membrane vesicles isolated from leaves of the wild-type and the Val(r)-2 mutant of Nicotiana tabacum L.

Transport of amino acids across the plasma membranes of various cell types is a key process in controlling the nitrogen balance of leaves. We studied the transport of the neutral amino acid L-valine into plasma membrane vesicles obtained by aqueous polymer two-phase partitioning of a microsomal fraction isolated from leaves of the wild-type and the Val(r)-2 mutant of tobacco (Nicotiana tabacum L.). Initial influxes were determined after the imposition of a pH-gradient (DeltapH, inside alkaline) and/or an electrical gradient (Deltapsi, inside negative) across the vesicle membrane. The initial magnitudes of the imposed gradients were DeltapH=2 and Deltapsi=-68 mV. In vesicles from the wild-type, the DeltapH-dependent valine influx could be analysed into a high-affinity (Km approximately 20 microM) and a low-affinity (Km approximately 3 mM) component. The influx of valine by the low-affinity system was stimulated about twofold, and that by the high-affinity system more than sixfold by the imposition of Deltapsi. This strong stimulation of the high-affinity system may indicate that it transports 2H+/amino acid. In the Val(r)-2 mutant the high-affinity component appeared to be completely absent.

Transport of amino acids (L-valine, L-lysine, L-glutamic acid) and sucrose into plasma membrane vesicles isolated from cotyledons of developing pea seeds.

Transport of the amino acids L-valine, L-lysine, and L-glutamic acid and of sucrose was studied in plasma membrane vesicles isolated from developing cotyledons of pea (Pisum sativum L. cv. Marzia). The vesicles were obtained by aqueous polymer two-phase partitioning of a microsomal fraction and the uptake was determined after the imposition of a H(+)-gradient (DeltapH, inside alkaline) and/or an electrical gradient (Deltapsi, inside negative) across the vesicle membrane. In the absence of gradients, a distinct, time-dependent uptake of L-valine was measured, which could be enhanced about 2-fold by the imposition of DeltapH. The imposition of Deltapsi stimulated the influx of valine by 20%, both in the absence and in the presence of DeltapH. Uptake of L-lysine was more strongly stimulated by Deltapsi than by DeltapH, and its DeltapH-dependent uptake was enhanced about 6-fold by the simultaneous imposition of Deltapsi. In the absence of gradients the uptake of L-glutamic acid was about 2-fold higher than that of L-valine, but it was not detectably affected by DeltapH or Deltapsi. Although the transport of sucrose was very low, a stimulating effect of DeltapH could be clearly demonstrated. The results lend further support to the contention that during seed development cotyledonary cells employ H(+)-symporters for the active uptake of sucrose and amino acids.

A plasma membrane-enriched fraction isolated from the coats of developing pea seeds contains H(+)-symporters for amino acids and sucrose.

Aqueous polymer two-phase partitioning was used to obtain a plasma membrane-enriched fraction from coats of developing pea (Pisum sativum L.) seeds in the filling stage. Uptake of amino acids and sucrose by vesicles from this fraction was determined after imposition of gradients of proton concentration (DeltapH, inside alkaline) and electrical potential (Deltapsi, inside negative) across the vesicle membrane. The uptake of sucrose and the amino acids L-valine, L-lysine, and L-glutamic acid was stimulated by the imposition of DeltapH. The imposition of Deltapsi, either in the presence or in the absence of DeltapH, stimulated the uptake of L-valine and L-lysine, but had no detectable effect on the uptake of sucrose and L-glutamic acid. The proton-motive-force-driven uptake of all four substrates was abolished by the protonophore carbonylcyanide m-chlorophenyl-hydrazone (CCCP). The results demonstrate the presence of H(+)-symporters for sucrose and amino acids in pea seed coats. This is running counter to the previously reported finding that their uptake by isolated pea seed coats was insensitive to CCCP, and that the uptake of sucrose, L-valine, and L-glutamic acid displayed linear kinetics. Possible causes of this discrepancy will be discussed.

Preoperative assessment of local tumor extent in advanced rectal cancer: CT or high-resolution MRI?

BACKGROUND: We compared high-resolution magnetic resonance imaging (MRI) with computed tomography (CT) in the assessment of tumor infiltration in surrounding structures for locally advanced primary and recurrent rectal cancer. METHODS: Twenty-six patients with operable, locally advanced rectal cancer (15 recurrent and 11 primary) were evaluated with conventional pelvic CT and 1.5-T high-resolution MRI with a quadrature phased-array coil. The images were scored for invasion of nine neighboring pelvic structures, and the results were compared with surgical and histologic findings. RESULTS: A total of 234 structures in 26 patients was evaluated for tumor invasion. For MRI the, sensitivity was 97% and the specificity 98%; for CT, the sensitivity was 70% and the specificity was 85%. The difference in performance was statistically significant (p<0.001). The failure most frequently made on CT was the false-positive prediction of pelvic floor and piriform muscle invasion (14), whereas MRI showed only four false-positive predictions. MRI correctly predicted all four cases of sacral bone invasion, three of which were missed by CT. MRI was accurate in 20 patients (80%) and CT in only five patients (19%). CONCLUSION: High-resolution MRI using a quadrature phased-array coil is highly accurate and superior to CT in predicting tumor infiltration in surrounding structures for locally advanced primary or recurrent rectal cancer and is recommended in the preoperative work-up of these tumors.

Prediction of spinal epidural metastases.

CONTEXT: Early diagnosis and treatment of spinal epidural metastases (SEM) is of the utmost importance to prevent neurological deficit due to spinal cord compression. Magnetic resonance imaging (MRI) has become the final tool in that diagnostic process. However, access to MRI is still limited in The Netherlands, requiring cost-effective use. It is generally acknowledged that patients with systemic cancer who present with a radiculopathy or myelopathy should undergo an MRI. However, the diagnostic policy in patients with systemic cancer who present with recently developed back pain is still a matter of debate. OBJECTIVE: To identify the patients with back pain in whom MRI can safely be omitted because of a low risk of SEM. METHODS: In a prospective series of 170 consecutive patients with cancer with recently developed back pain, prediction of spinal metastatic disease (SMD) and especially SEM was studied by means of a multivariate risk analysis of the parameters of the standard neurological evaluation (medical history, neurological examination, and plain films of the whole spine). Magnetic resonance imaging was used as the criterion standard. We calculated the risk implications of omitting MRI in patients with an estimated risk below different cutoff points. RESULTS: Spinal metastatic disease was diagnosed in 80 patients (47%); of these, 31 had SEM. A metastatic abnormality on plain films was the strongest independent predictor for SMD. Other important predictors were night pain, progressive pain, and Karnofsky score. Advanced age, exacerbation of pain during recumbency, and osteoporotic fracture imply a low risk of SMD. Night pain and the Karnofsky score proved to be the main predictors for SEM. A plain film showing an osteoporotic fracture strongly decreased the risk of SEM. The discriminating value of the multivariate analysis was too low, and too few patients can be excluded from undergoing MRI on the basis of the standard neurological checkup. To identify all the patients with SMD (P<.01), MRI would be excluded in only 7 patients. Identification of all patients with SEM (P<.001) reduced the number of MRIs by 21 at the expense of plain films of the whole spine for any patient. CONCLUSIONS: Selection of patients with cancer with back pain at risk of SEM was not possible with the standard neurological checkup. After intake by the neurologist, the next step should be MRI of the whole spine.

High-resolution magnetic resonance imaging of the anorectal region without an endocoil.

BACKGROUND: To evaluate the feasibility of a high-resolution magnetic resonance imaging (MRI) technique in detailed imaging of the anal sphincter and lower pelvic region without the use of an endoluminal coil. METHODS: MRIs with an external phased array coil (T1- and T2-weighted turbo spin echo) were performed in 22 volunteers and 12 patients with an anal fistula, an anal sphincter defect, or a rectal tumor. The normal scans were evaluated by three independent observers. The scans of the patients were compared with surgical and/or histologic findings. RESULTS: The anal sphincter was visualized with detail. In the anal canal, hemorrhoidal tissue and the submucosae ani muscle could be seen. The MRI technique also allowed detailed imaging of anatomical structures above the pelvic floor. The MR findings in the 12 patients showed exact correlation with surgery and/or histology. CONCLUSIONS: High-resolution MRI of the anorectal region without an endoluminal coil is feasible. The MR technique with an external phased array coil allows detailed imaging of the anal sphincter at rest, the rectum, and the surrounding pelvic structures with one single investigation. The results are promising and suggest useful applications in the management of anorectal diseases.

The Mechanism of Amino Acid Efflux from Seed Coats of Developing Pea Seeds as Revealed by Uptake Experiments.

The uptake of amino acids by excised seed coat halves of developing seeds of pea (Pisum sativum L.) was characterized. The influx of L-valine and L-glutamic acid was proportional to their external concentration, with coefficients of proportionality (k) of 11.0 and 7.1 [mu]mol g-1 fresh weight min-1 M-1, respectively. The influx of L-lysine could be analyzed into a component with linear kinetics (k = 8.1 [mu]mol g-1 fresh weight min-1 M-1) and one with saturation kinetics (Michaelis constant = 6.5 mM), but the latter may have resulted from the mutual interaction between the influx of the cationic lysine and the membrane potential. The influx of the amino acids was not affected by 10 [mu]M carbonylcyanide m-chlorophenylhydrazone, but was inhibited by about 50% in the presence of 2.5 mM p-chloromercuribenzene sulfonic acid. Conservative estimates of the permeability coefficients of the plasma membrane of seed coat parenchyma cells for lysine, glutamic acid, and several neutral amino acids were all in the range of 4 x 10-7 cm s-1 to 9 x 10-7 cm s-1, which is 4 to 5 orders of magnitude greater than those reported for artificial lipid bilayers. It is concluded that nonselective pores constitute a pathway in the plasma membrane for passive transport of amino acids. It is argued that this pathway is also used for the efflux of endogenous amino acids, the process by which nitrogen becomes available for the embryo.

The raz1 mutant of Arabidopsis thaliana lacks the activity of a high-affinity amino acid transporter.

The raz1 mutant of Arabidopsis thaliana (L.) Heynh. has been selected as resistant to the toxic proline analogue, azetidine-2-carboxylic acid (2AZ). Seedlings of the mutant tolerated fivefold higher concentrations of 2AZ (ED50 = 0.25 mM) than the wild-type seedlings (EC50 = 0.05 mM). The mutant gene was found to be semi-dominant and the corresponding RAZ1 locus was mapped on chromosome 5 at 69.6 +/- 1.8 cM. The resistance to 2AZ could be fully and exclusively accounted for by the lower uptake rate of the proline analogue in the mutant. The influx of L-proline in roots of wild-type seedlings could be dissected into two components: (i) a component with a high affinity and a low capacity for L-proline (Km) approximately 20 microM, Vmax approximately 60 nmol.(g FW)-1.h-1) and also a high affinity for L-2AZ (Ki approximately 40 microM) and (ii) a low-affinity, high-capacity component (Km) approximately 5 mM: Vmax = 1300 nmol.(g FW)-1.h-1). Clearly, the raz1 mutation affects the activity of a high-affinity transporter, because the high-affinity uptake of proline in the mutant was at least fivefold lower than in the wild-type, whereas the low-affinity uptake was unchanged.

Reversibility of lumbar epidural lipomatosis in obese patients after weight-reduction diet.

We present three obese patients with symptomatic lumbar epidural lipomatosis. All three were treated with a calorie-controlled diet and considerable weight reduction was achieved. MRI demonstrated a reduction in the epidural fat and relief of thecal sac compression in all three; two also improved clinically.

Lumbar epidural lipomatosis causing neurogenic claudication in two obese patients.

Two obese patients suffering from neurogenic claudication caused by lumbar epidural lipomatosis are described. Although lumbar epidural lipomatosis is most often related to prolonged use of steroid drugs, obesity has also been reported as a possible cause. Both CT and MRI can demonstrate excess epidural fat; because of the possibility of sagittal views MRI is to be preferred. In one of our patient with neurogenic claudication the excess epidural fat normalised completely after considerable weight reduction and symptoms resolved. Therefore weight reduction might be the initial therapy in an obese patient with symptomatic epidural lipomatosis. When weight reduction fails or when there are urgent clinical reasons, surgical removal of the excess amount of epidural fat should be considered.

Chronic obstructive pulmonary disease and abdominal aortic aneurysms.

In a prospective study during the period January-May 1992, 362 consecutive out-patients above 65 years of age, attending the pulmonary department for chronic obstructive airways disease (COPD), were ultrasonographically screened for an aneurysm of the abdominal aorta (AAA). Data from pulmonary function tests together with history of cardiac disease, diabetes mellitus, hypertension, hypercholesterolaemia, peripheral arterial obstructive disease, smoking and corticosteroid medication were collected. 30/282 men and 6/80 women with COPD had an AAA > or = 30 mm in diameter, which equals a prevalence of 9.9% (95% confidence limits: 6.8-13.0%). COPD patients with severe emphysema, having a decreased forced expiratory volume/vital capacity ratio (FEV/VC) of < 55%, have a significantly higher prevalence of aortic dilatation or AAA compared to COPD patients with mild or moderate decreased FEV/VC (chi-squared test: p < 0.05, alpha = 0.05). In the group of patients with AAA, significantly more smokers were seen compared to the group with normal and dilated aortas (chi-squared test: p < 0.05).

Balloon rupture and arteriovenous communication--a rare complication of transluminal angioplasty.

Arteriovenous Communication as a complication of PTA-procedure is rare. In the case presented a sharp sclerotic fragment probably caused a femoral AC and balloon rupture at the same time.

Compartmental analysis of amino-acid release from attached and detached pea seed coats.

Using the empty-seed-coat technique, we have studied the release of amino acids from pea (Pisum sativum L. cv. Marzia) seed coats, either attached to or detached from the mother plant, at various stages of development. During an experimental period of 8 h, about 70% of the amino-acid content of the seed coat was released into the solution with which the seed-coat cup was filled. Major components of the released amino-acid mixture were glutamine (25%), alanine (20%) and threonine (15%). At the end of the experimental period (t≥6 h) the amino-acid efflux from attached seed coats was approx. 0.15 µmol · h(-1)·(seed coat)(-1) greater than that from detached seed coats. This difference may be attributed to the import of amino acids into attached seed coats. It is equivalent to approx. 0.3 µmol N · h(-1) · (seed coat)(-1), whereas the nitrogen demand of the embryo amounted to 0.50 ± 0.04 µmol N · h(-1) · embryo(-1). The time course of the release from detached seed coats could be described by the sum of two exponentials with t1/2 = 0.4-0.7 h and t(1/2) = 3.3-6.9 h, respectively, which probably represent the emptying of the cytoplasmic and vacuolar compartments. During development the vacuolar amino-acid pool decreased considerably (from 6.2 to 1.4 µmol · (seed coat)(-1)), whereas the cytoplasmic pool was much more constant (2.1-1.2 µmol · (seed coat)(-1)). For attached seed coats it will be shown that the time course of the amino-acid release could be fully accounted for by the sum of two exponentials and a linear term, where the parameters of the exponentials were, within error, the same as for detached seed coats and the linear term represented the import of amino acids. The results will be discussed with reference to prevailing models of phloem unloading in the seed coat, and in relation to the flux of amino acids from seed coat to the developing embryo.