Location of major histocompatibility complex class II molecules in rafts on dendritic cells enhances the efficiency of T-cell activation and proliferation

The existence of major histocompatibility complex (MHC) class II molecules in lipid rafts has been described in dendritic cells (DC); however, the importance of rafts in T-cell activation has not been clarified. In this study, the distribution of the lipid raft components (CD59 and GM1 ganglioside) in human monocyte-derived DC was investigated. DC had an even distribution of these components at the cell surface. In addition, raft-associated GM1 ganglioside colocalized with cross-linked MHC class II. This implies coaggregation of raft components with these MHC molecules, which may be important in the interaction between T cells and antigen-presenting cells. In studies carried out to investigate the effect of the DC : T-cell interaction on raft distribution, we found a clustering of the lipid raft component CD59 on DC at the synaptic interface, with associated activation of the interacting T cell. In an antigen-specific response between DC and CD4+ T-cell clones, disruption of lipid rafts resulted in inhibition of both CD59 clustering and T-cell activation. This was most pronounced when limiting amounts of cognate peptide were used. Together, these data demonstrate the association of MHC class II with lipid rafts during DC : T-cell interaction and suggest an important role for DC lipid rafts in T-cell activation.

Inhibition of retinoic acid receptor signaling by Ski in acute myeloid leukemia

Acute myeloid leukemia (AML) is a heterogeneous disease with multiple different cytogenetic and molecular aberrations contributing to leukemic transformation. We compared gene expression profiles of 4608 genes using cDNA-arrays from 20 AML patients (nine with -7/del7q and 11 with normal karyotype) with 23 CD34+ preparations from healthy bone marrow donors. SKI, a nuclear oncogene, was highly up regulated. In a second set of 183 AML patients analyzed with real-time PCR, the highest expression level of SKI in AML with -7/del7q could be confirmed. As previously described, Ski associates with the retinoic acid receptor (RAR) complex and can repress transcription. We wanted to investigate the interference of Ski with RARalpha signaling in AML. Ski was co-immunoprecipitated and colocalized with RARalpha. We also found that overexpression of wild-type Ski inhibited the prodifferentiating effects of retinoic acid in U937 leukemia cells. Mutant Ski, lacking the N-CoR binding, was no more capable of repressing RARalpha signaling. The inhibition by wild-type Ski could partially be reverted by the histone deacetylase blocking agent valproic acid. In conclusion, Ski seems to be involved in the blocking of differentiation in AML via inhibition of RARalpha signaling.

Ion channels in cell proliferation and apoptotic cell death

Cell proliferation and apoptosis are paralleled by altered regulation of ion channels that play an active part in the signaling of those fundamental cellular mechanisms. Cell proliferation must--at some time point--increase cell volume and apoptosis is typically paralleled by cell shrinkage. Cell volume changes require the participation of ion transport across the cell membrane, including appropriate activity of Cl- and K+ channels. Besides regulating cytosolic Cl- activity, osmolyte flux and, thus, cell volume, most Cl- channels allow HCO3- exit and cytosolic acidification, which inhibits cell proliferation and favors apoptosis. K+ exit through K+ channels may decrease intracellular K+ concentration, which in turn favors apoptotic cell death. K+ channel activity further maintains the cell membrane potential, a critical determinant of Ca2+ entry through Ca2+ channels. Cytosolic Ca2+ may trigger mechanisms required for cell proliferation and stimulate enzymes executing apoptosis. The switch between cell proliferation and apoptosis apparently depends on the magnitude and temporal organization of Ca2+ entry and on the functional state of the cell. Due to complex interaction with other signaling pathways, a given ion channel may play a dual role in both cell proliferation and apoptosis. Thus, specific ion channel blockers may abrogate both fundamental cellular mechanisms, depending on cell type, regulatory environment and condition of the cell. Clearly, considerable further experimental effort is required to fully understand the complex interplay between ion channels, cell proliferation and apoptosis.

Cell volume regulatory ion transport in the regulation of cell migration

Cell migration is typically accomplished by the generation of protrusive mechanical forces and is achieved by repeated spatially and temporally coordinated cycles including the formation of a leading edge, the formation of new and disruption of older adhesions to the substratum, actomyosin based contractions and retraction of the trailing edge. Beside the well-described roles of the cytoskeleton and cell adhesions during these processes, a growing body of evidence indicates that the precise regulation of the cell volume is an indispensable prerequisite for coordinated cell migration. On the one hand during cell migration cell volume is continuously tormented by mechanical and morphological alterations, which pose changes to the intracellular hydrostatic pressure, metabolic changes and the formation or degradation of macromolecules like actin, which distort the osmotic equilibrium and the action of chemoattractants, hormones and transmitters, which frequently alter the electrical properties of a cell and thus cause cell swelling or shrinkage, respectively. On the other hand, a migrating cell actively has to govern cell volume regulatory ion transport mechanisms in order to create the appropriate micro- or even nanoenvironment in the intra- and/or extracellular space, which is necessary to guarantee the correct polarity and hence direction of movement of a migrating cell. This chapter will focus on the role of the cell volume regulatory ion transport mechanisms as they participate in the regulation of cell migration and special emphasis is given to their interplay with the cytoskeleton, their meaning for substrate adhesion and to the polarized fashion of their subcellular distribution.

Interferon-alpha2a is sufficient for promoting dendritic cell immunogenicity

Type I interferons (IFNs) are widely used therapeutically. IFN-alpha2a in particular is used as an antiviral agent, but its immunomodulatory properties are poorly understood. Dendritic cells (DCs) are the only antigen-presenting cells able to prime naive T cells and therefore play a crucial role in initiating the adaptive phase of the immune response. We studied the effects of IFN-alpha2a on DC maturation and its role in determining Th1/Th2 equilibrium. We found that IFN-alpha2a induced phenotypic maturation of DCs and increased their allostimulatory capacity. When dendritic cells were stimulated simultaneously by CD40 ligation and IFN-alpha2a, the production of interleukin (IL)-10 and IL-12 was increased. In contrast, lipopolysaccharide (LPS) stimulation in the presence of IFN-alpha2a mainly induced IL-10 release. The production of IFN-gamma and IL-5 by the responder naive T cells was also amplified in response to IFN-alpha2a-treated DCs. Furthermore, IL-12 production by IFN-alpha2a-treated DCs was enhanced further in the presence of anti-IL-10 antibody. Different results were obtained when DCs were treated simultaneously with IFN-alpha2a and other maturation factors, in particular LPS, and then stimulated by CD40 ligation 36 h later. Under these circumstances, IFN-alpha2a did not modify the DC phenotype, and the production of IL-10/IL-12 and IFN-gamma/IL-5 by DCs and by DC-stimulated naive T cells, respectively, was inhibited compared to the effects on DCs treated with maturation factors alone. Altogether, this work suggests that IFN-alpha2a in isolation is sufficient to promote DC activation, however, other concomitant events, such as exposure to LPS during a bacterial infection, can inhibit its effects. These results clarify some of the in vivo findings obtained with IFN-alpha2a and have direct implications for the design of IFN-alpha-based vaccines for immunotherapy.

Can Doppler time domain analysis of microembolic signals discriminate between gaseous and solid microemboli in patients with left ventricular assist device?

OBJECTIVE

Microembolic signals (MES) can be detected by transcranial Doppler sonography (TCD). To identify gaseous microemboli the inhalation of oxygen is an established method in patients with prosthetic heart valves. Time domain analysis of sample volume length (SVL) and of frequency modulation showed promising results in the discrimination between solid and gaseous microemboli. We investigated whether these time domain analyses allow the discrimination of different types of microemboli in patients with the non-pulsatile DeBakey left ventricular assist device (LVAD).

MATERIALS AND METHODS

Repeated unilateral detection of MES was performed by TCD in 20 patients supported with DeBakey LVAD. Each monitoring session consisted of 20 minutes without and 20 minutes with inhalation of 100% oxygen (6 l/min). A total of 500 MES, detected with (n=250) or without (n=250) the supply of oxygen, were randomly chosen for offline analysis. The SVL (in cm) was calculated by duration and velocity of the MES measured in the time domain mode. Additionally, frequency modulation of MES was classified into three main types: Without modulation (type I), with gradual changes (type II) and with rapid changes (type III).

RESULTS

With oxygen supply, both prevalence (26.4% versus 36.2%, p<0.01) and mean counts of MES per hour (49+/-293 versus 108+/-550, p<0.001) significantly declined compared with the MES load while breathing room air. There was no significant difference in the SVL of MES under oxygen (0.85+/-0.38 cm) compared with those without oxygen delivery (0.92+/-0.37 cm, p=0.6). Furthermore, no significant differences were noted for the MES frequency modulation types in time domain analysis with regard to oxygen supply.

CONCLUSIONS

The reduction of MES under oxygen delivery confirms the gaseous nature in a substantial number of circulating microemboli produced by the DeBakey LVAD. However, SVL and frequency modulation of MES did not appear to provide valuable information regarding the structural nature of the underlying microembolic material.

High level of cerebral microembolization in patients supported with the DeBakey left ventricular assist device

OBJECTIVE

Microembolic signals detected by transcranial Doppler ultrasonography have been demonstrated to be clinically relevant in patients supported with pulsatile left ventricular assist devices. We prospectively investigated the quantity of microembolic signals in patients supported with the continuous-flow DeBakey left ventricular assist device (MicroMed DeBakey VAD; MicroMed Technology, Inc, Houston, Tex) including the refined Carmeda BioActive Surface system (Carmeda AB, Stockholm, Sweden).

METHODS

Twenty-three patients (20 male) aged 14 to 62 years supported with DeBakey left ventricular assist devices (n = 6 with Carmeda) were enrolled in this study. Microembolic signal monitorings were performed twice weekly by insonating the middle cerebral artery for 20 minutes without and 20 minutes with oronasal application of oxygen (6 L/min). Evidence of clinically manifest thromboembolic events was based on regular questionnaires, clinical examinations, and results of diagnostic procedures.

RESULTS

Despite a low incidence of thromboembolic complications (0.24 per 100 left ventricular assist device days), 20 patients (87%) showed circulating microemboli. Overall, microembolic signals were found in 175 of 499 transcranial Doppler ultrasonographic examinations (35.1%), with mean counts of 81.2 +/- 443 (range 0-5042 signals/h). Both microembolic signal prevalence (25% vs 34%, P = .01) and absolute signal counts (46.5 vs 104, P < .01) significantly declined with oxygen delivery. There was no significant correlation between the individual microembolic signal activity and the incidence of clinical thromboembolism or the intensity of antihemostatic treatment. Patients supported with the Carmeda device did not show reduced rates of clinical thromboembolization or cerebral microemboli.

CONCLUSION

In patients with DeBakey left ventricular assist devices, a high load of clinically silent microemboli can be detected within the cerebral arteries despite a low incidence of embolic complications. It needs to be investigated whether such continuous, presumably gaseous microembolization causes cognitive or neuropsychologic deficits.

Caffeine inhibits cytokine expression in lymphocytes

Caffeine alters intracellular calcium signalling patterns in lymphocytes which are important for the specific regulation of activation and effector function in lymphocytes. The effect of caffeine on calcium signalling is probably mediated via a ryanodine receptor type 3 dependent intracellular calcium store which releases calcium after exposure to caffeine. Also, caffeine decreases lymphocyte cytotoxicity against allogenic myocyte. Which cytotoxic mechanisms are actually altered by caffeine is unknown. In mouse splenocyte cultures containing about 87% lymphocytes we show that concanavalin A (ConA, 5 microg/ml) stimulated cells increase the expression of TNF-alpha, IL-2 and IFN-gamma (ELISA) significantly. Caffeine (3.75 mM) inhibits cytokine expression of ConA stimulated cells almost completely. Ryanodine (1 microM) specifically blocks ryanodine receptors and thereby prevents caffeine induced calcium release. In our experiments, however, ryanodine has no effect on ConA stimulated IL-2 and IFN-gamma expression and only suppresses TNF-alpha expression by 20%. Furthermore, ryanodine does not prevent the inhibitory effect of caffeine on TNF-alpha, IL-2 and IFN-gamma expression in stimulated effector cells. We postulate that caffeine suppresses cytokine expression and thereby contributes to decreased cytotoxicity of lymphocytes against allogenic myocytes. The ryanodine receptor dependent intracellular calcium store does not seem to play a significant role in this process. Possibly, the blockade of IP3 receptors by caffeine is more important for cytokine suppression.

Increased prevalence of sleep apnea in patients with recurring ischemic stroke compared with first stroke victims

Since sleep apnea (SA) and stroke have many shared risk factors an independent contribution of SA to the overall risk of stroke is not easily proven and has been questioned recently. To contribute to this controversy, we analysed the frequency of SA in groups of patients with first and recurring ischemic stroke. We prospectively studied 102 patients admitted to our stroke unit. The prevalence of vascular risk factors and a history of previous stroke were recorded. All patients received cardio-respiratory polygraphy during the first 72 hours after admission. CT and MRI scans were evaluated for the location of the acute stroke and the presence of older vascular lesions. Thirty-four women and 68 men with a mean age of 64.5 +/- 13.7 years were included in the study. Cerebral lesions attributable to a previous stroke were identified in 25 patients, of whom 19 reported to have suffered a stroke before. Patients with stroke recurrence had a higher mean apnea-hypopnea index (AHI) (26.6/h vs. 15.1/h, p<0.05) and more often presented with a sleep apnea syndrome (SA) defined by an AHI >or=10/h (80 vs. 52%, p < 0.05) than patients with first ever stroke. Logistic regression analysis including the variables "age", "gender", "cumulative risk factors", "AHI >or=10/h", and "diabetes" identified diabetes (Odd's ratio [OR]=4.5) and AHI >or=10/h (OR=3.5) as independent risk-factors for stroke recurrence. According to our results SA is an independent risk factor for stroke recurrence. We therefore advocate routine sleep-apnea screening in all patients having suffered an ischemic stroke.

Local irradiation prior to stem cell harvest has no influence on CD34+ yield: a quantitative analysis

In patients with multiple myeloma, irradiation of bone marrow prior to mobilization of autologous peripheral blood progenitor cells (PBPCs) may lead to a reduced yield of CD34+ cells. Quantitative effects have not been sufficiently assessed. We retrospectively performed a multivariate analysis in 114 patients (67 men, 47 women) with multiple myeloma, of whom 53 (47%) patients had been irradiated prior to mobilization chemotherapy. High-dose cyclophosphamide followed by granulocyte colony-stimulating factor was used for mobilization in 84% of patients. In addition to previous chemotherapy, we quantitatively evaluated the dose and fractionation of prior irradiation, the volume of the irradiated bone marrow, and the time interval between radiation therapy and mobilization of PBPCs. The median volume of irradiated bone marrow was 9% (range 1-30%) of the estimated total hematopoietic bone marrow. The irradiated bone marrow volume and the number of CD34+ cells per kilogram of body weight in the first leukapheresis product showed no correlation. However, the time between irradiation and mobilization seemed to influence the yield of CD34+ cells. A comparison of irradiated patients with nonirradiated patients revealed no differences with respect to the CD34+ cell counts. We did not find a significant influence of the extent or the total dose of irradiation on the yield of CD34+ cells in the first leukapheresis product in patients with multiple myeloma. However, there may be an inverse correlation between the time elapsed since the last irradiation and the number of mobilized CD34+ cells.

Pneumonia in acute stroke patients fed by nasogastric tube

BACKGROUND

Aspiration pneumonia is the most important acute complication of stroke related dysphagia. Tube feeding is usually recommended as an effective and safe way to supply nutrition in dysphagic stroke patients.

OBJECTIVE

To estimate the frequency of pneumonia in acute stroke patients fed by nasogastric tube, to determine risk factors for this complication, and to examine whether the occurrence of pneumonia is related to outcome.

METHODS

Over an 18 month period a prospective study was done on 100 consecutive patients with acute stroke who were given tube feeding because of dysphagia. Intermediate outcomes were pneumonia and artificial ventilation. Functional outcome was assessed at three months. Logistic regression and multivariate regression analyses were used, respectively, to identify variables significantly associated with the occurrence of pneumonia and those related to a poor outcome.

RESULTS

Pneumonia was diagnosed in 44% of the tube fed patients. Most patients acquired pneumonia on the second or third day after stroke onset. Patients with pneumonia more often required endotracheal intubation and mechanical ventilation than those without pneumonia. Independent predictors for the occurrence of pneumonia were a decreased level of consciousness and severe facial palsy. The NIH stroke scale score on admission was the only independent predictor of a poor outcome.

CONCLUSIONS

Nasogastric tubes offer only limited protection against aspiration pneumonia in patients with dysphagia from acute stroke. Pneumonia occurs mainly in the first days of the illness and patients with decreased consciousness and a severe facial palsy are especially endangered.

Immunobiology and gene-based immunotherapy of hepatocellular carcinoma

PURPOSE

Hepatocellular carcinoma (HCC) is one of the major malignancies worldwide. For most patients with advanced or multifocal HCC treatment options are limited resulting in a poor prognosis. Several local ablation methods have been developed as minimally invasive strategies for HCC treatment. It is unclear, until now, whether these therapies will significantly improve the poor prognosis of patients with unresectable HCC. Novel therapeutic strategies and a better understanding of HCC imunobiology are, therefore, urgently required.

DESIGN

The scientific literature since 1970 in all languages cited in Medline was systematically reviewed.

RESULTS

Until now, a variety of specific and non-specific immunostimulatory strategies against HCC has been applied in preclinical experimental models with some promising results. The molecular characterization of HCC associated tumour antigens such as alpha-fetoprotein (AFP) and the increased understanding of the immunological pathways involved in liver and tumor immunology have paved the way for the design of promising gene-based cancer vaccines. The first phase I and II immunotherapeutic clinical trials based on dendritic cell immunotherapy and peptide vaccines are ongoing in HCC-patients. Clinical trials have, in general, demonstrated the safety of such strategies. Recently, exciting new immunological techniques and tools have been developed which allow to characterize antigen specific T cells at a single-cell level. In future, HCC specific tumor rejection antigens which can be used therapeutically have to be identified using microarray-based analysis. The different therapeutic modalities need to be compared directly resulting in optimised therapeutic approaches and the identification of sub-groups of HCC-patients responding favourably to treatment.

Lemierre's syndrome: the forgotten disease. An unusual presentation of sepsis

A 19-year-old girl presented with a septical condition with fever of 40 degrees C, swelling of the right sternocleidomastoid region and abdominal pain. Except for a sore throat with pain strictly localized to the right side of her neck and fever over the last week there were no other clues in her past medical history. An abdominal ultrasound and MRT scan as well as a chest X-ray only showed non-specific findings. The diagnosis of Lemierre's syndrome was established by ultrasonographical detection of right jugular venous thrombosis and perivascular inflammation together with blood cultures positive for Fusobacteria. The patient recovered within days after treatment was initiated with metronidazol according to the antibiogram. Lemierre's syndrome is a life-threatening disease especially in an age group which is less frequently affected by septicaemia. A history of sore throat, Fusobacterium positive blood cultures and ultrasonographical detection of jugular venous thrombophlebitis together with the knowledge of the "forgotten disease" will lead the way to the diagnosis.

Right-to-Left-Shunts Detected by Transesophageal Echocardiography and Transcranial Doppler Sonography

BACKGROUND

Transesophageal echocardiography (TEE) and transcranial Doppler sonography (TCD) can identify right-to-left-shunts that predispose to paradoxical embolism. In a large cohort we compared the results of both techniques.

METHODS

222 patients were investigated by both techniques using the contrast agent Echovist-300 and performing each test once without and once with the Valsalva maneuver (VM).

RESULTS

TEE-proven right-to-left-shunts were detected by TCD with a high sensitivity of 94%. In addition, TCD revealed shunts not noted during TEE in about 20% of all patients studied. These shunts are in general smaller than those concordantly identified; however, 9% of the patients without a TEE-proven shunt presented with a shunt that allows a considerable amount of contrast medium to pass. There were 12% more microbubbles detected in the right middle cerebral artery than in the left middle cerebral artery during the TCD test performed with VM, but not during the TCD test performed without VM.

CONCLUSIONS

Contrast-enhanced TEE and TCD are complementary methods in the assessment of stroke and stroke-prone patients. The side difference of microbubbles may indicate a selective streaming of cardiac emboli during VM.

Microembolus Detection in Four Patients with Fabry’s Disease: Further Support for a Primarily Microangiopathic Origin of Early Cerebrovascular Symptoms

Fabry's disease is a sex-linked recessive storage disorder leading to cerebrovascular symptoms in many cases. Whether the primary origin of cerebrovascular symptoms in these patients is due to autochthonous thrombosis of small vessels or embolic infarction from large vessels is under debate. Microembolic signals (MES) indicative of an active embolic source can be recorded by transcranial Doppler sonography. We report four patients (34, 44, 62 and 66 years old) with Fabry's disease from one kindred in whom we carried out microembolus detection recordings to disclose active embolic sources. Three of the patients had had transient focal neurological deficits. Two patients had angina pectoris and one had exercise dyspnea, but no patient had clear evidence of disease of the large coronary vessels or brain-supplying arteries. No MES were found in 1-hour recordings in any patients, supporting the hypothesis that early cerebrovascular symptoms arise from small vessel occlusion and not from embolic sources as an indicator of disease of large brain-supplying arteries or cardiac embolism.

On the origin of microembolic signals

BACKGROUND AND PURPOSE

Clinically silent circulating microembolic signals (MES) can be identified by transcranial Doppler ultrasound (TCD). It is not yet clear whether their occurrence is always linked to the presence of embolic sources.

METHODS

24 terminally ill patients (7 women, 17 men; mean age 68 years) were investigated by TCD of the middle cerebral arteries. These findings were correlated with a complete post-mortem examination of potential embolic pathways.

RESULTS

Four patients out of the 24 under investigation showed MES, 2 of them bilaterally. All these 4 MES-positive patients had a definite embolic source, i. e. bilateral carotid artery occlusive disease, endocarditis with thrombotic valvular adhesions and severe plaques in the aortic arch, dilated left atrium and a patent foramen ovale, or severe plaques in the aortic arch and a dilated left atrium, respectively.

CONCLUSION

In the investigated patient group, we could demonstrate that MES can only be found when an embolic source is present. The finding of MES justifies an extensive clinical and laboratory search for potential embolic sources including extracranial and intracranial colour-coded duplex ultrasound, ECG, Holter-ECG, and TEE.

Contrast transcranial Doppler ultrasound in the detection of right-to-left shunts: comparison of Echovist-200 and Echovist-300, timing of the Valsalva maneuver, and general recommendations for the performance of the test

BACKGROUND AND PURPOSE

Cardiac right-to-left shunts (RLS) can be identified by transesophageal echocardiography (TEE) as well as by transcranial Doppler ultrasound (TCD) using contrast agents, such as Echovist-200 or Echovist-300 in conjunction with a Valsalva maneuver (VM) as provocation procedure. Both Echovist preparations are in use. Currently, the appropriate timing of the VM is still under debate.

METHODS

Sixty-four patients were investigated by both TEE and bilateral TCD of the middle cerebral arteries. The following protocol was applied in a randomized way: (1) no VM, (2) VM for 5 s starting with the beginning of Echovist-300 injection, (3) VM for 5 s starting 5 s after the beginning of Echovist-300 injection, (4) VM for 5 s starting 10 s after the beginning of Echovist-300 injection, and (5) VM for 5 s starting 5 s after the beginning of Echovist-200 injection.

RESULTS

In 27 patients, an RLS was demonstrated by both TEE and contrast TCD (shunt-positive). Twenty-two patients were negative in both investigations, no patient was positive on TEE but negative on TCD, 15 patients were only positive on at least one TCD investigation but negative on TEE. Tests 3 and 5 were the most appropriate ones; test 3 was slightly superior to test 5.

CONCLUSIONS

TCD using Echovist-300 or Echovist-200 is a sensitive method to identify TEE-proven cardiac RLS. To achieve the best diagnostic accuracy, the VM should be performed for a duration of 5 s starting at 5 s following the beginning of contrast injection.

Optimizing the technique of contrast transcranial Doppler ultrasound in the detection of right-to-left shunts

BACKGROUND AND PURPOSE

A cardiac right-to-left shunt (RLS) can be identified by transesophageal echocardiography and transcranial Doppler ultrasound (TCD) with contrast agents and a Valsalva maneuver (VM) as a provocation procedure. This article applies the modalities of these tests detailed in previous studies to a large patient cohort and compares 2 contrast agents (saline and Echovist-300).

METHODS

Eighty-one patients were investigated by both transesophageal echocardiography and bilateral TCD of the middle cerebral arteries. The following protocol with injections of 10 mL agitated saline was applied in a randomized way: (1) no VM, (2) VM for 5 seconds starting 5 seconds after the beginning of contrast injection, and (3) repetition of the test with VM if the first test with VM was negative. The VM was performed for 5 seconds starting exactly 5 seconds after the beginning of saline injection. Thereafter, the same protocol was repeated with 10 mL Echovist-300 instead of saline.

RESULTS

Thirty-one patients had a cardiac RLS. The Echovist-300 investigation disclosed all these 31 shunts, but saline disclosed only 29 of them. Twenty-two had an RLS only in at least 1 of the above TCD tests, some of them even with a considerable shunt volume.

CONCLUSIONS

Contrast TCD performed with Echovist-300 but not with saline yields a 100% sensitivity to identify transesophageal echocardiography-proven cardiac RLSs. The TCD test should be repeated if negative the first time. This article gives detailed information for the optimization of the contrast TCD technique. Extracardiac shunts detected only during contrast TCD can have a considerable shunt volume and may allow for paradoxical embolism.

Molecular and functional aspects of anionic channels activated during regulatory volume decrease in mammalian cells

The ability of cells to readjust their volume after swelling, a phenomenon known as regulatory volume decrease (RVD), is a fundamental biological achievement guaranteeing survival and function of cells under osmotic stress. This article reviews the mechanisms of RVD in mammalian cells with special emphasis on the activation of ion channels during RVD.

Circulating microemboli in 33 patients with intracranial arterial stenosis

BACKGROUND

Intracranial arterial stenosis is a rare cause of stroke in Caucasians. Detection of clinically silent circulating microemboli by transcranial Doppler sonography is now widely investigated in patients with carotid artery disease in the hope to identify patients at increased risk for stroke.

METHODS

In 33 patients with intracranial internal carotid (n = 12), middle cerebral (n = 18), posterior cerebral (n = 2), or basilar artery stenosis (n = 1), we performed a 1-hour microembolus detection downstream to the stenosis in the middle or in the posterior cerebral artery, respectively. The stenosis was assessed by transcranial Doppler and duplex ultrasound. 18 patients had been symptomatic in the dependent territory.

RESULTS

Five patients with ischaemic symptoms within the last 8 days and with a peak systolic flow velocity of > or =210 cm/s in the stenosis showed microembolic signals at a rate of 3-25 events/h, despite effective anticoagulation. All these 5 patients had a lesion pattern on cranial CT or MRI scan suggesting embolic origin. All the asymptomatic patients (n = 15) and all the patients with a peak systolic intrastenostic velocity of 160 to <210 cm/s (n = 13) did not show microembolic signals at all.

CONCLUSION

Microembolic signals occur in recently symptomatic patients with high-grade intracranial arterial stenosis indicated by a sonographically measured stenotic peak flow velocity of > or =210 cm/s. Therapeutic anticoagulation was not sufficient to suppress microemboli formation.

Automatic classification of HITS into artifacts or solid or gaseous emboli by a wavelet representation combined with dual-gate TCD

BACKGROUND AND PURPOSE

Transcranial Doppler (TCD) can detect high-intensity transient signals (HITS) in the cerebral circulation. HITS may correspond to artifacts or solid or gaseous emboli. The aim of this study was to develop an offline automated Doppler system allowing the classification of HITS.

METHODS

We studied 600 HITS in vivo, including 200 artifacts from normal subjects, 200 solid emboli from patients with symptomatic internal carotid artery stenosis, and 200 gaseous emboli in stroke patients with patent foramen ovale. The study was 2-fold, each part involving 300 HITS (100 of each type). The first 300 HITS (learning set) were used to construct an automated classification algorithm. The remaining 300 HITS (validation set) were used to check the validity of this algorithm. To classify HITS, we combined dual-gate TCD with a wavelet representation and compared it with the current "gold standard," the human experts.

RESULTS

A combination of the peak frequency of HITS and the time delay makes it possible to separate artifacts from emboli. On the validation set, we achieved a sensitivity of 97%, a specificity of 98%, a positive predictive value (PPV) of 99%, and a negative predictive value (NPV) of 94%. To distinguish between solid and gaseous emboli, where positive refers now to the solid emboli, we used the peak frequency, the relative power, and the envelope symmetry of HITS. On the validation set, we achieved a sensitivity of 89%, a specificity of 86%, a conditional PPV of 89%, and a conditional NPV of 89%.

CONCLUSIONS

An automated wavelet representation combined with dual-gate TCD can reliably reject artifacts from emboli. From a clinical standpoint, however, this approach has only a fair accuracy in differentiating between solid and gaseous emboli.

Myocyte function and [Ca 2+ ]i homeostasis during early allogenic heart transplant rejection

BACKGROUND

Recent studies from our laboratory have demonstrated that in vivo contractile function of rejecting mouse heterotopic abdominal heart allografts 5 days after transplantation is depressed to 40% of that of syngenic controls, and that this depression of function is prevented by the nitric oxide synthase (NOS) inhibitor NG-monomethyl-l-arginine. However, the mechanisms of altered myocyte function caused by nitric oxide production in this setting are not established.

METHODS

We measured intracellular calcium concentration ([Ca2+]i) transients (fluo-3, confocal microscopy), fractional shortening (video motion), and L-type Ca2+ currents (whole-cell patch clamp) 5 days after transplantation in ventricular myocytes freshly isolated from syngenic (Balb/C into Balb/C) and allogenic (Balb/C into C3H) transplants.

RESULTS

L-type Ca2+ currents, [Ca2+]i transient amplitudes, and fractional shortening did not differ between nonrejecting, syngenic and rejecting, allogenic transplants. Catecholamine responsiveness as analyzed by the change in the peak [Ca2+]i transient induced by 100 nM isoproterenol was also similar. Superfusion with l-arginine, an NOS substrate, caused decreased shortening with no change in [Ca2+]i transients in allogenic myocytes, but had no effect in syngenic myocytes.

CONCLUSIONS

Depressed contractile function of rejecting allogenic heart transplants in vivo appears to be caused in part by an NOS-dependent decrease in myofilament Ca2+ sensitivity.

Early growth response-1 gene: potential radiation response gene marker in prostate cancer

This study was undertaken to determine whether the transcription factor EGR-1 expression: (1) in the primary tumor, correlates with radiation response in terms of complete local tumor control with no evidence of disease or recurrence and no evidence of metastasis; (2) in the postirradiated biopsies correlates with residual tumor; and (3) correlates with the expression of Egr-1 target genes such as TP53, pRB, and Bax. The authors analyzed: (1) 25 pretreated surgically resected paraffin-embedded primary adenocarcinomas of the prostate for the presence of EGR-1 expression and mutation, and correlated this with clinical endpoints such as serum prostate-specific antigen levels and current clinical status; (2) 27 postirradiated biopsies of prostate for the presence of EGR-1 expression, and correlated these findings to the residual tumor status; and (3) 12 prospective prostate tumor specimens for EGR-1 expression and its target genes. EGR-1 expression was determined by immunohistochemistry and mutations were screened in two regions of the Egr-1 gene (trinucleotide AGC repeats in transactivation domain [TD] and poly A tract in 3'UTR) by polymerase chain reaction-single strand conformational polymorphism analysis. Of 25 patients, 18 patients showed expression of EGR-1. EGR-1 overexpression correlated with treatment failure. No correlation with EGR-1 overexpression and its target genes was found, which may indirectly suggest that overexpressed EGR-1 may lack transactivation function. In summary, EGR-1 overexpression in the mutant form may provide an indication of clinical failure (local recurrence or metastasis).

Functional importance and caffeine sensitivity of ryanodine receptors in primary lymphocytes

Calcium signaling patterns are important for the specific regulation of activation and effector function in lymphocytes. Studies of [Ca2+]i regulation in lymphocytes, including the involvement of ryanodine receptors (RyR) and the importance of caffeine-sensitive pools, have been carried out mainly in lymphocyte cell lines and the presence and functional importance of these pools in primary lymphocytes has not been addressed. Here we show by confocal microscopy that caffeine caused a prompt but transitory increase of [Ca2+]i in primary lymphocytes, an effect that was inhibited by pre-treatment with ryanodine. Furthermore, the increase of [Ca2+]i in CD4+ and CD8+ MLR T lymphocytes stimulated by 5 microg/ml concanavalin A was significantly inhibited by pretreatment with caffeine. In functional studies, caffeine decreased cytotoxicity against myocyte target cells which is probably related to an altered calcium signaling in CD8+ MLR lymphocytes. Caffeine also terminated spontaneous Ca2+ oscillations and induced a rise in [Ca2+]i in CD4- and CD8- MLR lymphocytes probably of B cell origin. These results demonstrate that caffeine alters Ca2+ signaling in primary lymphocytes, and suggest that RyR, probably the skeletal muscle receptor (RyR-1) and brain receptor (RyR-3), are involved in mediating this effect. It is also possible that blocking of inositol-1,4,5-triphosphate (IP3) receptors is involved in the effects of caffeine on lymphocyte activation.

[Possibilities and limits of outpatient antibiotic therapy of infective endocarditis]

BACKGROUND

Infective endocarditis has a high morbidity and lethality. Therefore antibiotic treatment has to be intravenous to achieve high blood levels and has to last several weeks without an interruption of treatment at the weekends.

PATIENT SELECTION FOR OUTPATIENT THERAPY

It is therefore crucial to select the patient group that is suited for an outpatient, antibiotic therapy very carefully. In general only hemodynamically stable patients without complications in whom the responsible organism has been identified should be considered.

TREATMENT

From a pharmacological point of view intravenous or intramuscular application for the complete duration of therapy is obligatory. Endocarditis caused by penicillin-susceptible streptococci, the biggest group of organisms responsible for endocarditis, can be treated with Ceftriaxon once daily for 4 weeks. For other organisms there are at present no data available which support the feasibility of an outpatient therapy. In particular antibiotic therapy with a complex regimen for those organisms is not practicable for outpatient usage. Possibly, in the near future computer controlled pumps might overcome this disadvantage.

LIMITS

Every outpatient therapy should be initiated under inpatient conditions and only after an initial response to the antibiotic therapy continued in an outpatient setting. Today reliable outpatient therapy and follow-up 7 days a week under the given outpatient infrastructure is problematic and remains an exception. However, considering cost-effectiveness outpatient as compared to inpatient antibiotic therapy could be an interesting economically advantageous alternative.

Inhibin, activin, and follistatin in human fetal pituitary and gonadal physiology

BACKGROUND

Activin has been previously demonstrated to directly stimulate the synthesis of gonadotropin-releasing hormone (GnRH) receptors and to increase follicle-stimulating hormone (FSH) secretion in nonhuman pituitary cell cultures (PCCs). Currently, knowledge of the physiological role of these peptides in primates is still far from complete. Moreover, several results in macaque monkeys failed to support an unequivocal role for inhibin in FSH suppression. Whereas the bioactivity of inhibin and activin has been demonstrated in rat PCCs, no data exist on human pituitary response to these peptides either in vivo or in vitro.

METHODS

We studied the secretion of FSH and luteinizing hormone (LH) by dispersed human fetal pituitary cells from midtrimester abortions in response to recombinant human (rh-) activin-A, inhibin-A, and other secretagogues. After mechanical and enzymatic dispersion, the human fetal pituitary cells were cultured on an extracellular matrixlike-material-coated 24-well plate. After 3 days' incubation in serum-containing medium, the PCCs were washed and preincubated for 90 min in serum-free medium and incubated with activin-A, inhibin-A, TGF-beta, follistatin, sex steroids, and GnRH, in quadruplicate.

RESULTS

Activin-A was a potent secretagogue for FSH secretion. GnRH (20 ng/ml) was more potent than rh-activin-A for LH secretion. Nevertheless, a significant increase in LH secretion into the medium was brought about by rh-activin-A. Inhibin decreased FSH and LH secretion, but the LH response to inhibin was less prominent than that of FSH. GnRH opposed the inhibitory effect of inhibin on LH secretion. In dynamic, short-term, repetitive exposure of fetal pituitary fragments to rh-activin-A (superfusion), we could not receive a similar increase in LH and FSH as in static incubations, as opposed to a short GnRH exposure. In addition to their endocrine, paracrine, and autocrine effects, and in addition to their role as possible markers, the TGF-beta superfamily members may affect embryogenesis and possibly immunomodulation of the embryo and fetus. The role of activin and inhibin as intragonadal regulators is hypothesized. The pro-alphaC inhibin precursor may act as an FSH receptor antagonist.

CONCLUSIONS

Human fetal PCCs express the previously reported physiologic responses to activin and inhibin generated in nonhuman experiments on gonadotropin secretion in vitro and may serve as a physiologic model for studying human gonadotrope responses to the TGF-beta family of peptides.

Determination of protein-protein interactions of ICIn by the yeast two-hybrid system

ICln is a ubiquitously expressed eukaryotic protein. Expression of the protein in Xenopus laevis oocytes, the knocking-down of the protein in fibroblasts, or the reconstitution of the protein in lipid bilayer led to the assumption that this protein is an ionic channel or a significant part thereof. However, other possible roles for ICln in potential regulatory mechanisms have been postulated, as diverse as regulator of cell morphology by interacting with the Skb1 protein and/or interaction with core spliceosomal proteins. Here we show that ICln is able to interact with SnRNP core proteins SmD1, SmD2, SmD3, SmX5 and SmB/B'.

Na(+)/H(+)exchangers: linking osmotic dysequilibrium to modified cell function

The Na(+)/H(+) exchangers (NHEs) are among the major ion transporters involved in cell volume regulation. NHE activation leads to a cellular influx of Na(+) ions and extrusion of H(+) ions, which are readily replenished from intracellular buffers. This will result in a net import of Na(+). In many systems NHE operates in parallel to Cl(-)/ HCO3(-) exchange, resulting in cellular uptake of NaCl. The influx of osmotically obliged water will consequently lead to cell swelling. This makes NHEs suitable to serve as powerful mechanisms for increasing cell volume (CV). The low volume threshold for NHE activation enables the cells to respond to very minute reductions of the CV. By the coupling to the export of H(+) ions cell volume regulatory NHE activation may lead to changes in intracellular pH. On the other hand NHEs are activated by a broad variety of ligands and by intracellular acidosis, which, in turn, may consequently lead to cell swelling. In addition, NHEs are linked to other intracellular proteins and structures, like e.g. the cytoskeleton, which themelves are involved in the regulation of numerous cellular processes. Therefore NHEs link CV regulation to a diversity of cellular functions, both in physiological and pathophysiological conditions. Six isoforms of the Na(+)/H(+) exchanger, termed NHE1--6, have been cloned so far. NHE 1--5 are located in the plasma membrane, whereas NHE6 is sorted to the mitochondrial membrane. NHE1 and NHE6 are the ubiquitously expressed isoforms. The expression of the isoforms NHE2 to NHE5 is restricted to specific tissues and the pattern of their expression, as well as their subcellular localization indicate that they fulfill specialized functions. Cell shrinkage induced activation has been shown for NHE1,2 and 4. In contrast, NHE3 is inhibited by cell shrinkage. In many cells several isoforms are present and assigned to specific membrane domains where they may serve a functional crosstalk between the different ion transporters.

Is alpha/beta for prostate tumors really low?

PURPOSE

Brenner and Hall's 1999 paper estimating an alpha/beta value of 1.5 Gy for prostate tumors has stimulated much interest in the question of whether this ratio (of intrinsic radiosensitivity to repair capacity) is much lower in prostate tumors than in other types of tumors that proliferate faster. The implications for possibly treating prostatic cancer using fewer and larger fractions are important. In this paper we review updated clinical data and present somewhat different calculations to estimate alpha/beta.

METHODS AND MATERIALS

Seventeen clinical papers published from 1995 to 2000 were reviewed to obtain estimates of biochemical control from radiotherapy alone using external beam, I-125 implants, or Pd-103 implants. The focus was on intermediate risk patients. Three methods of estimating alpha/beta were employed. First, a simple two-step graphical comparison of isoeffective doses from external beam and implant modalities was made, to see which value of alpha/beta predicted the observed identity of biologic effect. Second, the same data were subjected to Direct Analysis (maximum likelihood estimation), from which an estimate of alpha/beta and also of the T(12) of repair of sublethal damage in the tumors (both with confidence intervals) were obtained. Third, preliminary clinical data comparing two different sizes of high-dose boost doses were analyzed in which significantly different bNED was observed at 2 years.

RESULTS

The second method gave the definitive result of alpha/beta = 1.49 Gy (95% CI 1.25-1.76) and T(12) = 1.90 h (95% CI 1.42-2.86 h). The first method gave a range from 1.4 to 1.9 Gy and showed that if mean or median dose were used instead of prescribed dose, the estimate of alpha/beta would be substantially below 1 Gy. The third method, although based on early follow-up, was consistent with low values of alpha/beta in the region of 2 Gy or below. The estimate for T(12) is the first value reported for prostate tumors in situ.

CONCLUSIONS

All the estimates point toward low values of alpha/beta, at least as low as the estimates of Brenner and Hall, and possibly lower than the expected values of about 3 Gy for late complications. Hypofractionation trials for intermediate-risk prostatic cancer appear to be indicated.

Effects of deletion of muscle LIM protein on myocyte function

Muscle LIM protein (MLP) may serve as a scaffold protein on the actin-based cytoskeleton, and mice deficient in this protein (MLPKO) have been recently reported to develop dilated cardiomyopathy. To determine the causes of depressed contractility in this model, we measured intracellular Ca2+ concentration ([Ca2+]i) transients (fluo 3), cell shortening, L-type Ca2+ channel current ( I Ca,L), Na/Ca exchanger current ( I Na/Ca), and sarcoplasmic reticulum (SR) Ca content in left ventricular MLPKO myocytes. I Ca,L-voltage relationships, I Na/Ca density, and membrane capacitance did not differ between wild-type (WT) and MLPKO myocytes. The peak systolic [Ca2+]i was significantly increased in MLPKO myocytes (603 ± 54 vs. 349 ± 18 nM in WT myocytes). The decline of [Ca2+]i transients was accelerated in MLPKO myocytes, and SR Ca2+ content was increased by 21%, indicating that SR Ca2+-ATPase function is normal or enhanced in MLPKO myocytes. Confocal imaging of actin filaments stained with tetramethylrhodamine isothiocyanate-labeled phalloidin showed disorganization of myofibrils and abnormal alignment of Z bands, and fractional shortening was significantly diminished in MLPKO myocytes compared with that in WT myocytes at comparable peak [Ca2+]i. Thus a reduced [Ca2+]-induced shortening may be involved in the pathogenesis of myocardial dysfunction in this genetic model of heart failure.

Adipophilin is a sensitive marker for lipid loading in human blood monocytes

Adipophilin, a marker of lipid accumulation initially described in adipocytes, was recently shown to be induced in macrophage foam cells. We found that even freshly isolated blood monocytes express adipophilin and that the amount of adipophilin protein is variable in monocytes from different healthy individuals. However, the physiological expression of adipophilin does not correlate with the levels of free fatty acids, cholesterylesters or free cholesterol. Enzymatically modified low-density lipoprotein (E-LDL) induces rapid foam cell formation in monocytes and upregulates adipophilin mRNA and protein within 2 h of incubation. This rapid induction of adipophilin is accompanied by a significant increase of free fatty acids in monocytes incubated with E-LDL. Adipophilin facilitates the uptake of free fatty acids, and here we demonstrate that free fatty acids increase is related to the early upregulation of adipophilin expression in blood monocytes. Fatty acids are ligands for peroxisome proliferator-activated receptor-gamma (PPARgamma), and the upregulation of adipophilin mRNA by PPARgamma agonists like 15d-PGJ(2) and ciglitazone indicates that PPARgamma may mediate the induction of adipophilin expression in human blood monocytes.

ATP-binding cassette transporter A1 (ABCA1) affects total body sterol metabolism

BACKGROUND AND AIMS

Members of the family of ABC transporters are involved in different processes of sterol metabolism, and ABCA1 was recently identified as a key regulator of high-density lipoprotein (HDL) metabolism. Our aim was to further analyze the role of ABCA1 in cholesterol metabolism.

METHODS

ABCA1-deficient mice (ABCA1-/-) and wild-type mice were compared for different aspects of sterol metabolism. Intestinal cholesterol absorption was determined by a dual stable isotope technique, and analysis of fecal, plasma, and tissue sterols was performed by gas chromatography/mass spectrometry. Key regulators of sterol metabolism were investigated by Northern and Western blot analyses or enzyme activity assays.

RESULTS

ABCA1-disrupted sv129/C57BL/6 hybrid mice showed a significant reduction in intestinal cholesterol absorption. The decrease in cholesterol absorption was followed by an enhanced fecal loss of neutral sterols, whereas fecal bile acid excretion was not affected. Total body cholesterol synthesis was significantly increased, with enhanced 3-hydroxy-3-methyglutaryl-coenzyme A (HMG-CoA) reductase observed in adrenals and spleen. In addition, ABCA1-/- mice showed markedly increased concentrations of cholesterol precursors in the plasma, lung, intestine, and feces. Reduced HMG-CoA reductase messenger RNA and enzyme activity in the liver suggest that enhanced cholesterol synthesis in ABCA1-/- mice occurs in peripheral tissues rather than the liver.

CONCLUSIONS

The metabolism of cholesterol and cholesterol precursors is markedly affected by a lack of ABCA1 function.

Interaction of CD163 with the regulatory subunit of casein kinase II (CKII) and dependence of CD163 signaling on CKII and protein kinase C

CD163 is a recently identified member of the scavenger receptor cysteine-rich superfamily, which is expressed on peripheral blood monocytes and most tissue macrophages and is thought to play an important role in the regulation of the inflammatory response of these cells. Cross-linking of CD163 on glucocorticoid-stimulated macrophages results in the secretion of several proinflammatory cytokines, but the precise mechanism of CD163 mediated signal transduction is not understood. The existence of several CD163 isoforms, which differ in the structure of their cytoplasmic domains and putative phosphorylation sites, suggests that these isoforms also differ in their signaling mechanism. Using the Yeast Two-Hybrid system and further in vitro and in vivo studies, we identified the regulatory beta-subunit of casein kinase II (CKII), which specifically binds to the cytoplasmic domain of CD163 and its isoforms. We also found, that in vitro the CD163 isoforms differ in their association with the CKII holoenzyme and in the phosphorylation by CKII. Furthermore, we demonstrated that the cytoplasmic domains of CD163 variants are phosphorylated by PKC-alpha in vitro. Inhibition studies using specific kinase inhibitors reveal that both CKII and PKC are involved in the CD163 signaling mechanism resulting in the secretion of proinflammatory cytokines.

Cell volume in the regulation of cell proliferation and apoptotic cell death

Cell proliferation must - at some time point - lead to increase of cell volume and one of the hallmarks of apoptosis is cell shrinkage. At constant extracellular osmolarity those alterations of cell volume must reflect respective changes of cellular osmolarity which are hardly possible without the participation of cell volume regulatory mechanisms. Indeed, as shown for ras oncogene expressing 3T3 fibroblasts, cell proliferation is paralleled by activation of Na(+)/H(+) exchange and Na(+),K(+),2Cl(-) cotransport, the major transport systems accomplishing regulatory cell volume increase. Conversely, as evident from CD95-induced apoptotic cell death, apoptosis is paralleled by inhibition of Na(+)/H(+) exchanger and by activation of Cl(-) channels and release of the organic osmolyte taurine, major components of regulatory cell volume decrease. However, ras oncogene activation leads to activation and CD95 receptor triggering to inhibition of K(+) channels. The effects counteract the respective cell volume changes. Presumably, they serve to regulate cell membrane potential, which is decisive for Ca(++) entry through I(CRAC) and the generation of cytosolic Ca(++) oscillations in proliferating cells. As a matter of fact I(CRAC) is activated in ras oncogene expressing cells and inhibited in CD95-triggered cells. Activation of K(+) channels and Na(+)/H(+) exchanger as well as Ca(++) oscillations have been observed in a wide variety of cells upon exposure to diverse mitogenic factors. Conversely, diverse apoptotic factors have been shown to activate Cl(-) channels and organic osmolyte release. Inhibition of K(+) channels is apparently, however, not a constant phenomenon paralleling apoptosis which in some cells may even require the operation of K(+) channels. Moreover, cell proliferation may at some point require activation of Cl(-) channels. In any case, the alterations of cell volume are obviously important for the outcome, as cell shrinkage impedes cell proliferation and apoptosis can be elicited by increase of extracellular osmolarity. At this stage little is known about the interplay of cell volume regulatory mechanisms and the cellular machinery leading to mitosis or death of the cell. Thus, considerable further experimental effort is required in this exciting area of cell physiology.

Structure and function of the ion channel ICln

Normal function of organs and cells is tightly linked to the cytoarchitecture. Control of the cell volume is therefore vital for the organism. A widely established strategy of cells to counteract swelling is the activation of chloride and potassium channels, which leads to a net efflux of salt followed by water - a process termed regulatory volume decrease. Since there is evidence for swelling-dependent chloride channels (IClswell) being activated also during pathological processes, the identification of the molecular entity underlying IClswell is of utmost importance. Several proteins are discussed as the channel forming IClswell, i.e. phospholemman, p-glycoprotein, CLC-3 and ICln. In this review we would like to focus on the properties of ICln, a protein cloned from a Madin Darby canine kidney (MDCK) cell library whose expression in Xenopus laevis oocytes resulted in a nucleotide sensitive outwardly rectifying chloride current closely resembling the biophysical properties of IClswell.