Brain structural alterations associated with dysfunctional cognitive control of pain in patients with low back pain.

BACKGROUND: Recent evidence has shown that chronic back pain (CBP) can lead to functional alterations in the circuitry underlying the cognitive control of pain. Thought suppression (TS) is a common type of cognitive control of pain. Previous research has shown that TS has paradoxical effects that may increase the awareness of pain. Pain-related TS may also increase individuals' attention to pain, which may also increase pain sensation, but thus far, the relationship between pain-related TS and structural brain alterations is unknown. METHODS: In this study, we investigated a group of 30 patients 6 months after lumbar disc surgery by applying voxel-based morphometry (VBM) to identify brain regions correlated with TS scores. RESULTS: Since pain-related TS has been positively correlated with depression, all calculations were controlled for depression and age. VBM revealed a negative correlation between the TS score and regional grey matter volume (GMV) in the left superior temporal gyrus (LSTG) and the left middle temporal gyrus (L MTG), which is part of the left temporoparietal junction (L TPJ). In addition, a mediation analysis revealed a significant mediation effect of the pain-related TS on the association between GMV of the left TPJ and reported pain intensity in the last 7 days. CONCLUSIONS: These findings are consistent with previous research on the dysfunctional cognitive control of pain and may therefore provide potential insights into the neural substrates of obstructive cognitive control in chronic low back pain, with a special emphasis on pain-related TS. SIGNIFICANCE: The link between pain-related thought suppression and brain morphology may provide a new perspective on the understanding of cognitive control of pain in chronic low back pain, which may help improve cognitive behavioural therapy.

Cervical cord and ventricle affection in neuromyelitis optica.

OBJECTIVES: Cervical cord involvement is common in neuromyelitis optica (NMO) and multiple sclerosis (MS), but its impact on disability in NMO has rarely been studied. Recent publications on NMO examined the periventricular system, areas of high aquaporin-4 expression, but not yet by using ventricle volumetry. PURPOSE: To compare cervical cord atrophy, ventricular widening, and supra- and infratentorial brain measures between NMO and MS, and study their impact on clinical disability. METHODS: Magnet resonance imaging-based volumetry of upper cervical cord, third and fourth lateral ventricles, grey matter, white matter, brainstem, cerebellum and clinical status of 18 NMO and 20 MS patients, was compared between the groups and with 26 healthy controls. Patterns of ventricular widening relative to healthy controls were inspected by voxel-based morphometry of the cerebrospinal fluid. RESULTS: Cervical cord atrophy was similar in NMO and MS (75.2 ± 10.0 mm2 , respectively, 76.5 ± 9.5 mm2 vs 84.1 ± 8.6 mm2 in controls).Third ventricle increase in both groups, and specific fourth ventricle widening in MS were detected. Patient groups differed in third to fourth ventricle ratio (P = 0.002). In NMO, white matter correlated inversely with the affected cord segments (P = 0.001) and with cervical cord area (P = 0.043). The disability status was explained by cervical cord area and third ventricle volume (R2 =0.524) in NMO, and by grey matter and fourth ventricle volume (R2 =0.565) in MS. CONCLUSION: Cervical cord atrophy and third ventricular enlargement are both clinically relevant in NMO. Third and fourth ventricle volumetry shows differences between NMO and MS regarding the involvement of periventricular structures.

Cervical cord area is associated with infratentorial grey and white matter volume predominantly in relapsing-remitting multiple sclerosis: A study using semi-automated cord volumetry and voxel-based morphometry.

BACKGROUND AND PURPOSE: Atrophy of the brain and the upper cervical cord, which both have major impact on the severity of clinical symptoms in multiple sclerosis (MS), may be interrelated by neuraxonal degeneration. Aiming to identify possible spatially remote effects of neuraxonal brain damage on spinal cord atrophy, we studied regional and global brain volumes and the upper cervical cord area (UCCA) in a large group of MS patients and a healthy control group. METHODS: In a group of 132 MS patients (71 relapsing-remitting MS; 61 secondary progressive MS; median [range] of EDSS: 5 [0-7], respectively 6 [2-8.5] and mean±standard deviation of age/disease duration: 37±11 years/6.7±6.3 years; respectively: 49±8 years/14.5±8.0 years) and 45 healthy subjects UCCA, regional and global brain volumes, and brain lesion load were assessed. Associations between MRI results and clinical parameters in the entire cohort and differentiated according to MS-subtype were investigated using t-tests, partial correlation analyses, voxel-based morphometry and statistical parametric mapping. RESULTS: Exclusively in RRMS, a significant positive correlation of UCCA with cerebellar cortical grey matter (GM) in the vermis and with regional white matter volume in the entire brainstem, corresponding to the corticospinal tracts, was detected. Although SPMS patients were considerably more affected by disability and decrease of UCCA (RRMS:75.2±10.4 mm(2); SPMS: 66.0±11.8 mm(2),controls: 84.5±8.7mm(2)), brain grey matter (RRMS:585.8±53.6 ml; SPMS: 528.2±61.5 ml, controls: 608.7±48.1 ml) and total brain volume (RRMS:1162.9±41.8 ml; SPMS: 1117.9±51.2 ml, controls: 1194.1±19.5 ml) than RRMS patients, significant positive associations in this group were found only between UCCA and a cluster of white matter in the medulla, but not in grey matter. CONCLUSION: Cervical cord and brain atrophy were present in both, RRMS and even more severe in SPMS. Still, spatial associations between cervical cord area and remote cerebellar and brainstem volume, possibly driven by neuraxonal degeneration, were detected mostly in RRMS patients with predominantly short disease durations. Future longitudinal studies may elucidate the interplay between affection of spinal cord and infratentorial structures in MS, and contribute to the understanding of the conversion processes from relapsing-remitting to secondary progressive MS.

A morphometric cadaver study of the anterior lumbar epidural space.

INTRODUCTION: Free disc fragments end often up in the concavity of the anterior epidural space. This space consists of two compartments. The discrepancy between the impressive magnetic resonance imaging findings, clinical symptoms in patients and the problem of treatment options led us to the anatomical determination of anterior epidural space volumes. MATERIALS AND METHODS: For the first time, the left and right anterior epidural volume between the peridural membrane and the posterior concavity of the lumbar vertebral bodies L3-S1 were determined for each segment. A CT scan and a polyester resin injection were used for the in vitro measurements. RESULTS: The volumes determined in human cadavers using this method ranged from 0.23 ccm for L3 to 0.34 ccm for L5. The CT concavity volume determination showed this increase in volume from cranial to caudal, as well. CONCLUSION: This volume is large enough to hold average-sized slipped discs without causing neurological deficits. A better understanding of the anterior epidural space may allow a better distinction of patient treatment options.

Quantitative assessment of brain stem and cerebellar atrophy in spinocerebellar ataxia types 3 and 6: impact on clinical status.

BACKGROUND AND PURPOSE: Cerebellar and brain stem atrophy are important features in SCA3, whereas SCA6 has been regarded as a "pure" cerebellar disease. However, recent neuropathologic studies have described additional brain stem involvement in SCA6. We, therefore, aimed to investigate the occurrence and impact of regional infratentorial brain volume differences in patients with SCA3 and SCA6. MATERIALS AND METHODS: Thirty-four patients with genetically proved SCA (SCA3, n = 17; SCA6, n = 17) and age-matched healthy control subjects (n = 51) were included. In all subjects, high-resolution T1-weighted images were acquired with a 1.5T MR imaging scanner. Individual brain stem and cerebellar volumes were calculated by using semiautomated volumetry approaches. For all patients with SCA, clinical dysfunction was scored according to the ICARS. Multiple regression analysis was used to identify the contribution of regional volumes to explain the variance in clinical dysfunction in each SCA genotype. RESULTS: Cerebellar volumes were lower in patients with SCA6 compared with controls and with those with SCA3. In contrast to controls, brain stem volume loss was observed in patients with SCA3 (P < .001) and, to a lesser extent, in those with SCA6 (P = .027). Significant linear dependencies were found between ICARS and cerebellum volume (SCA3: R(2) = 0.29, P = .02; SCA6: R(2) = 0.29, P = .03) and between ICARS and brain stem volume (SCA3: R(2) = 0.49, P = .002; SCA6: R(2) = 0.39, P < .01) in both subtypes. Both cerebellar and brain stem atrophy contributed independently to the variance in clinical dysfunction in SCA6, while in SCA3, only brain stem atrophy was of relevance. CONCLUSIONS: Our current findings in accordance with recent neuroradiologic and pathoanatomic studies suggest brain stem and cerebellar volume loss as attractive surrogate markers of disease severity in SCA3 and SCA6.

[Prevention and management of postoperative complications in pancreatic surgery]. / Prävention und Management von postoperativen Komplikationen in der Pankreaschirurgie.

During the last decades mortality after pancreatic surgery has decreased. Nevertheless, morbidity still remains at a high level. It is important to differentiate between pancreatic head resection and distal pancreatectomy. The complication rates of both procedures are high, however the need for intervention to manage perilous complications is higher after pancreaticoduodenectomy. The main complications after pancreatic surgery are delayed gastric emptying (DGE), pancreatic fistula, anastomotic leakage and bleeding. The current literature on the different techniques of pancreatic anastomosis and pancreatic remnant closure, respectively, does not show consistent results or an advantage for a particular technique. The same is true for the perioperative use of somatostatin and its analogues for the prevention of complications. It is widely agreed that the smooth texture of the pancreas and a small pancreatic duct < 3 mm are risk factors for pancreatic leakage or fistula. Today, the trend is more for conservative or interventional therapy for pancreatic fistulas or intraabdominal collections with, e. g., persisting intraoperative drain, TPN, somatostatin therapy or CT-controlled drainage. The opinions about the optimal treatment of the dreaded postoperative bleeding differ significantly in the surgical community. There are early and late bleedings and the management varies from endoscopical treatment or angiographic coiling / stenting to revision. Nevertheless, every bleeding is accompanied with high mortality. Here we present a review of literature and demonstrate the various strategies for the management of complications.

MR venography in the detection of pelvic venous congestion.

PURPOSE: To investigate the feasibility of using magnetic resonance venography (MRV) to detect pelvic venous congestion (PVC). METHODS: A prospective study of 23 female patients with signs and symptoms of PVC, who underwent duplex sonography, MRV and phlebography (P). Examinations were interpreted in a blinded fashion. Visualization of venous anatomy, presence of venous incompetence and congestion grade were evaluated. Sensitivity and specificity of MRV using P as reference were calculated. RESULTS: MRV agreed with P in 96% (Cohen-K-value 0.646) and in 70% (K 0.555) of the cases respectively in the venous anatomy and congestion grade. Sensitivity and specificity of MRV were 88% and 67% for ovarian veins, 100% and 38% for hypogastric veins and 91% and 42% for the pelvic plexus. CONCLUSIONS: In this prospective study MRV showed high sensitivity in the evaluation of patients with suspected PVC. Routine use of this diagnostic method requires further studies in larger patient cohorts.

Is initial success of thrombolytic therapy with rt-PA in patients with lower limb ischemia durable? A long-term follow-up series.

BACKGROUND: Catheter-directed intraarterial thrombolytic therapy with rt-PA has been established as an alternative to surgery in selected patients with lower limb ischemia. The purpose of this study is to evaluate its long-term results and to try to identify patient variables influencing outcome. PATIENTS AND METHODS: The results of thrombolytic treatment for acute or subacute lower limb ischemia in 82 patients (51 male, 31 female) were retrospectively analysed. Clinical data (time of symptoms onset, clinical stage, type of affected vessel, anatomical localisation) as well as comorbidities were recorded. The success rate of thrombolysis as well as the incidence of adverse events was evaluated. Patients with initial success were followed up after a median of 52,5 months. RESULTS: Thrombolytic therapy was successful in 67 cases (82%). An additional endovascular or surgical procedure was necessary in 39 of these patients (48%). The overall bleeding rate was 18% and the mortality and major amputation rate was 1%. 42 patients with early clinical success were available for follow-up. 34 of them (81%) were free of ischemic symptoms and the overall limb salvage rate was 96%. We could not identify factors significantly influencing early or long-term results, although there was a trend towards better results in patients with acute ischemia and in patients with occluded native arteries. CONCLUSIONS: Intraarterial local thrombolytic therapy has a relatively high initial success rate in selected patients with lower limb ischemia, but is associated with a significant number of bleeding complications. Furthermore, additional procedures are required in almost half the patients. Initial success is durable at the long-term in the majority of cases. Better selection of patients and refinements of the thrombolytic therapy might help to further improve results and lower the bleeding complications.

Daphnia behavioural responses to taste and odour compounds: ecological significance and application as an inline treatment plant monitoring tool.

Continuous monitoring of volatile organic compounds (VOC) in raw water is highly desirable for taste and odour management, but in most treatment plants this capacity is lacking. We used a bbe Daphnia toximeter installed in the Zurich water treatment plant to determine if Daphnia magna could be used to monitor odour compounds in source-water. Trace levels of two widely distributed biogenic VOCs in freshwater: P-cyclocitral and 2(E),4(E),7(Z)-decatrienal were added to the raw water inflow to chambers containing test animals and their behaviour was recorded using a high resolution camera. We observed that each compound elicited a marked short-term increase in Daphnia swimming velocity, but the effect was brief and an acclimation to the compounds was observed after a time period or with repeated additions. The results demonstrate that the toximeter has considerable potential as a tool to monitor certain VOCs in water, and that Daphnia perceive and react to 2(E),4(E),7(Z)-decatrienal and P-cyclocitral at concentrations between 2.5 and 25 microM.

Diffusion tensor imaging-based fractional anisotropy quantification in the corticospinal tract of patients with amyotrophic lateral sclerosis using a probabilistic mixture model.

BACKGROUND AND PURPOSE: In amyotrophic lateral sclerosis (ALS), fiber degeneration within the corticospinal tract (CST) can be quantified by diffusion tensor imaging (DTI) as an indirect marker of upper motor neuron involvement. A new method of measuring quantitative DTI parameters using a probabilistic mixture model for fiber tissue and background in the corticospinal tract of patients with ALS is evaluated. MATERIALS AND METHODS: Axial echo-planar imaging (EPI) DTI datasets (6 gradient directions, 10 repetitions) were acquired for 10 patients and 20 healthy control subjects. The diffusion tensor was visualized in a multiplanar viewer using a unique color coding method. Pure fiber tissue inside a region is separated from background and mixture voxels using a probabilistic mixture model. This allows for a reduction of errors as a result of partial volume effects and measurement variability. RESULTS: Fractional anisotropy (FA) was measured within the CST at levels ranging from internal capsule to pons. Mean coefficients of variation of intrarater, scan-rescan, and inter-rater reproducibility were 2.4%, 3.0%, and 5.7%, respectively. Optimal measurement positions along the CST with respect to minimum variability and maximum difference between patients and healthy subjects were identified in the caudal half of the internal capsule. Moreover, a negative correlation between the age-corrected FA and the disease duration but not the ALS Severity scale score was found. CONCLUSION: The new software for fiber integrity quantification is suited to assess FA in the corticospinal tract with high reproducibility. Thus, this tool can be useful in future studies for monitoring disease status and potential treatment efficiency.

Superior mesenteric artery aneurysm stent graft.

Visceral artery aneurysms represent 0.1% to 0.2% of all vascular aneurysms. They are mostly asymptomatic, but rupture is associated with a high mortality rate. We present a case of an asymptomatic aneurysm of the proximal superior mesenteric artery in a 64-year-old man that was successfully treated by implantation of a covered stent graft. The use of endovascular techniques to manage visceral artery aneurysms should be considered.

Impact of apomorphine on BOLD signal during movement in normals.

Our group investigated modulatory effects of apomorphine on cerebral activation patterns during finger tapping movements in six healthy right-handed volunteers using an established fMRI protocol. Apomorphine application disclosed a reduction of cerebral activation to the contralateral precentral and postcentral gyrus and ipsilateral cerebellum, with a prominent net reduction of BOLD signal in cerebellar areas. These findings contradict those of similar studies performed on dopaminergic function and Parkinson's disease (PD), which predominantly found augmentation of cerebral activation patterns in normal volunteers and PD patients after dopaminergic stimulation. One conceivable explanation for our singular results would be preferred binding of apomorphine to presynaptic dopaminergic receptors, leading to inhibition of endogenous dopamine release and resultant diminished dopaminergic stimulation, reflected in diminished cerebral activation patterns. These findings warrant future consideration and further investigation of possible central inhibitory effects of dopaminergic therapy in functional imaging studies of the dopaminergic system in general and PD in particular.

[Direct MR-arthrography of the shoulder with maximum capsular distension for surgical planning]. / Direkte MR-Arthrographie des Schultergelenks mit maximaler Kapseldistension zur OP-Planung.

PURPOSE: To evaluate the effectiveness of direct MR arthrography of the glenohumeral joint with maximum distension of the joint capsule in patients with glenohumeral instability for preoperative diagnosis and for determining the method of surgical intervention. MATERIALS AND METHODS: MR arthrography of the shoulder joint was performed on a 1.5 T system in 38 patients. All patients suffered from anterior or bidirectional instability. Using a fluoroscopically guided posterior approach, a 1 % dilution of dimeglumine gadopentetate (5 mmol Gd-DTPA/l) was injected until full capsular stretching was achieved. MR imaging protocol included fat-saturated transversal, oblique-coronal and oblique-sagittal T1-weighted spin-echo, T1-weighted 3-D and transversal T2-weighted Flash-2D. RESULTS: MR imaging revealed significant capsule distention in 22 patients and ventral capsule defects in 9 patients. Labral lesions were depicted in 25 patients, bicipital tendon lesions in 4 patients and partial ruptures of the rotator cuff in 3 patients. 15 of the 38 patients underwent surgery. Areas of pathologic laxity of the glenohumeral capsule were correctly described in all cases. In 12 of 15 patients, the best method of intervention could be determined prospectively. In 3 of 15 patients, the necessary operation was overestimated. Regarding labral ruptures, MRI had a sensitivity of 88 %, a specificity of 86 %, and a diagnostic accuracy of 87 %. CONCLUSION: Direct glenohumeral MR arthrography allows accurate preoperative evaluation of labral and tendinous structures. Judging the capsular laxity allows the determination of the optimal method of surgical intervention. The maximum extent of a stabilizing operation can be predicted preoperatively.

[Lumbar intraspinal juxtafacet cysts: MR imaging and CT-arthrography]. / Lumbale intraspinale Juxta-Facettenzysten: Kernspintomographie und CT-Arthrographie.

PURPOSE: To present data on the MR imaging appearance of lumbar intraspinal juxtafacet cysts (JFC) and to assess the importance of additional CT arthrography. MATERIAL AND METHODS: Twenty-eight patients (16 women, 12 men) with a mean age of 64 years (range: 43 - 82), who underwent MR imaging because of radicular pain or spinal claudication, were found to have an intraspinal cyst associated with the facet joint. In 14 patients, additional CT-arthrography was performed to determine whether a communication exists between the cyst and the facet joint and to try to rupture the cyst. RESULTS: In T(2)-weighted images, juxtafacet cysts show a typical pattern consisting of a hyperintense center and hypointense rim. The center is likely to be inhomogeneous because of recurrent hemorrhage in the cyst. In T1-weighted images, the cysts are hypo/isointense. Irregular hyperintensity may indicate subacute hemorrhage, which may aggravate the clinical symptoms. MR allows superior visualization of the cyst in all anatomical planes. It also enables assessment of typical accompanying changes, such as degenerative spondylolisthesis and facet hypertrophy. All patients, who had CT-arthrography, were found to have a direct communication between joint space and cyst. Transarticular rupture of the cyst was possible in five patients. Two of these five patients had good to excellent improvement, and the remaining three patients underwent surgery. CONCLUSION: MR imaging is the method of choice for diagnosing lumbar intraspinal juxtafacet cysts. CT-arthrography of the facet joint is helpful in cases with difficult differential diagnosis, and in the preoperative planning. Furthermore, it assists in the primary interventional treatment.

Macroangiopathy of the upper extremities in progressive systemic sclerosis.

BACKGROUND: Raynaud's phenomenon is a hallmark of progressive systemic sclerosis (SSc). While nailfold capillary changes are well known, morphological changes in larger arteries have less been focused on. OBJECTIVE AND METHODS: In the study presented we examined how often in digital subtraction angiography organic changes of the arteries of the fingers, hands and forearms were observed, whether they showed a typical picture like the changes in nailfold capillaries and whether they correlated with cutaneous sclerosis, Raynaud's phenomenon and serological findings. 29 patients were examined, 14 with acroscleroderma and 15 with proximal ascending sclerosis. RESULTS: In 27 of those 29 patients a stenosis of the arteries of the upper extremity was found. The frequency of arterial occlusions decreased from the fingers (26 patients) to the forearms (9 patients with occlusion of the ulnar artery, none with occlusion of the radial artery). The arteries of 47% of patients with proximal ascending sclerosis showed no reactivity towards the alpha-sympatholyticum tolazoline hydrochloride due to severe organic changes while in patients with acroscleroderma only 14% of patients did not respond to tolazoline hydrochloride. The severity of Raynaud's phenomenon did not correlate with the severity of the angiographic findings. In patients with stenoses refractory to tolazoline hydrochloride and in those with occlusions Scl-70 autoantibodies were more frequently positive than in other patients with SSc (44% compared to 23%). CONCLUSION: As in SSc the severity of the organic arterial changes is in close correlation with the extent of the cutaneous sclerosis and with the serological findings the arterial system should gain much more importance in the diagnosis and therapy of SSc.

Qualitative and quantitative analysis of voice onset by means of a multidimensional voice analysis system (MVAS) using high-speed imaging.

High-speed filming is one of the most informative methods for assessing voice physiology data. Tracing high-speed images of the glottis provides quantitative parameters such as the glottal area and the glottal width function. By way of example, a number of studies are discussed which extract quantitative data from high-speed images showing voice onsets. Furthermore, a new computer system (MVAS; multi-dimensional voice analysis system) is presented that synchronously displays a laryngoscopic high-speed film, the electroglottographical signal, and several acoustic analyses of the recorded voice sample. The automatic measurement of glottal width and glottal area from the laryngoscopic images is also provided. Looking at former studies and our analyses of voice onsets reveals a tremendous intersubject and even intrasubject variability (different prephonatory closure, different time span until full amplitude is reached, different open quotient).

Contrast-enhanced transcranial color-coded sonography in acute hemispheric brain infarction.

PURPOSE: The aim of the present study was to investigate the diagnostic potential of contrast-enhanced transcranial color-coded real-time sonography (CE-TCCS) in otherwise ultrasound-refractory acute stroke patients with an ischemia in the territory of the middle cerebral artery (MCA). Furthermore, correlations of CE-TCCS findings with clinical, angiographic, and CT results were investigated. METHODS: In 90 acute stroke patients with inadequate insonation conditions in unenhanced transcranial color-coded real-time sonography (TCCS) examinations, CE-TCCS, clinical, angiographic, and CT examinations were performed within 12 hours, 36 hours (CE-TCCS only), and 1 week after onset of clinical symptoms. A CT angiography (CTA) as reference method was available in 39 individuals. After application of a galactose-based echo-enhancing agent, the portion of conclusive ultrasound examinations of the MCA, as manifested by an MCA occlusion, decreased or increased flow velocity (FV), and symmetrical MCA FV, was evaluated. CE-TCCS findings on admission and during follow-up were correlated with infarction size as demonstrated on follow-up CT, and clinical findings were assessed by use of the European Stroke Scale. RESULTS: Adequate diagnosis was achieved in 74 of 90 patients (82%) by the use of echo contrast agents. MCA occlusion or reduction of MCA FV was found in 20 and 27 patients, respectively. MCA occlusion was confirmed by CTA in 17 cases. In one individual, false-positive diagnosis of MCA occlusion was made according to ultrasound criteria. In 5 patients with MCA occlusion, vessel recanalization was observed during follow-up; 15 of 27 patients with decreased flow velocities showed normalization after the third examination that was associated with a significantly better clinical outcome (P<0.0001). Furthermore, MCA occlusion or decreased FV in the first 12 hours were associated with significantly larger infarctions in the MCA territory compared with normal CE-TCCS findings (P<0.0001). CONCLUSIONS: CE-TCCS enables adequate diagnosis in approximately 80% of acute hemispheric stroke patients with insufficient unenhanced TCCS examinations. It is a reliable diagnostic tool regarding MCA mainstem and branch occlusions. Because this method conveys useful information concerning cerebral tissue and clinical prognosis, it may be useful to identify those patients who benefit most from local or intra-arterial thrombolytic therapy.

NH4+ utilization and regeneration rates in freshwater lakes determined by GC-MS of derivatised dihydroindophenol.

A new gas chromatographic-mass spectrometric method was established that is applicable for the determination of NH4+ utilization and regeneration rates in freshwater. Hollow-fibre modules were used to stop the biogenic nitrogen-fluxes by separating the particulate from the dissolved matter. Incubations were performed in Tedlar bags (polyvinylfluoride), which enabled repeated sample removals through Teflon tubes, making the calculation of nitrogen-fluxes in accordance to Blackburn and Caperon much more reliable. The Berthelot reaction was performed with ammonium and a fragment ion (base peak) of tris-(trifluoroacetyl) 4,4'-dihydroxydiphenylamine was used to determine the at% excess 15N by gas chromatography-mass spectrometry. Nitrogen-flux measurements were made in the epilimnion of the deep, stratified, mesotrophic Lake Zürich, in which the cyanobacterium Planktothrix rubescens was the dominating photoautotrophic micro-organism. The size fraction <20 microm that consisted of heterotrophic bacterioplankton and nanoflagellates, and photoautotrophic pico- and nanoplankton accounted only for a minor part of the ammonium utilization (<25%) and regeneration (< or =25%) rates, whereas the size fraction >20 microm which primarily consisted of Planktothrix rubescens was responsible for the major part. In the eutrophic Lake Au, which is connected to Lake Zürich through a canal, utilization and regeneration rates as high as 700 and 482 nM h(-1) were measured.

Characterization of a [Ca2+]i-dependent current in human atrial and ventricular cardiomyocytes in the absence of Na+ and K+.

OBJECTIVES: In situations of [Ca2+]i-overload, arrhythmias are believed to be triggered by delayed afterdepolarizations, which are generated by a transient inward current ITI. This study was designed to examine [Ca2+]i-dependent membrane currents in the absence of the Na+/Ca(2+)-exchanger as possible contributors to ITI in human cardiac cells. METHODS: The whole cell voltage clamp technique was used for electrophysiological measurements in human atrial and ventricular cardiomyocytes. [Ca2+]i-measurements were performed using the fluorescent Ca(2+)-indicator fura-2. All solutions were Na(+)-free. Voltage-independent [Ca2+]i-transients were elicited by rapid caffeine applications. RESULTS: In atrial myocytes, caffeine induced a transient membrane current in the absence of Na+ and K+. This current could be suppressed by internal EGTA (10 mM). Cl- did not contribute to this current. Experiments with different cations suggested non-selectivity for Cs+ and Li+, whereas N-methyl-D-glucamine appeared to be impermeable. Voltage ramps indicated a linear current-voltage relation in the range of +80 to -80 mV. Fluorescence measurements revealed a dissociation between the time courses of current and bulk [Ca2+]i-signal. In ventricular cardiomyocytes, caffeine failed to induce transient currents in 54 cells from 22 different patients with or without terminal heart failure. CONCLUSIONS: In human atrial cardiomyocytes, a [Ca2+]i-dependent nonspecific cation channel is expressed and may contribute to triggered arrhythmias in situations of [Ca2+]i-overload. No evidence could be found for the existence of a [Ca2+]i-dependent chloride current in atrial cells. In ventricular cells, neither a [Ca2+]i-dependent nonspecific cation channel nor a [Ca2+]i-dependent chloride channel seems to be expressed. Possible delayed afterdepolarizations in human ventricular myocardium might therefore be carried by the Na+/Ca(2+)-exchanger alone.