Search PubMed⌕ Search

Biomedical subjects

H Klein

Publications and source records attributed to H Klein.

At least 37 records · Page 2Linked to original sources
PubMed2001

Characterization and crystallization of a novel Sarcocystis muris lectin, SML-2.

A novel lectin (SML-2) consisting of 138 amino acids was isolated from cyst merozoites of Sarcocystis muris and sequenced by Edman degradation and mass spectrometry. All 12 cysteinyl residues are involved in disulfide bridges, four of which are attributed to a characteristic pattern of cysteines as found in the so-called PAN-module superfamily. Crystals of SML-2 diffracting to 2.1 A resolution at a synchrotron were grown by the hanging-drop vapour-diffusion technique. They belong to the space group P2(1)2(1)2(1), with unit-cell parameters a = 53.6, b = 128.8, c = 158.2 A and eight molecules in the asymmetric unit. SML-2 cocrystallized with Au galactose results in two different crystal forms. The first form is isomorphous with the native crystals and the second form adopts space group C222(1), with unit-cell parameters a = 74.7, b = 82.0, c = 131.0 A, and diffracts to 2.4 A at a rotating-anode X-ray generator.

Amino Acid Sequence↗
PubMed2001

Activation of an ATP-dependent K(+) conductance in Xenopus oocytes by expression of adenylate kinase cloned from renal proximal tubules.

In rabbit proximal convoluted tubules, an ATP-sensitive K(+) (K(ATP)) channel has been shown to be involved in membrane cross-talk, i.e. the coupling (most likely mediated through intracellular ATP) between transepithelial Na(+) transport and basolateral K(+) conductance. This K(+) conductance is inhibited by taurine. We sought to isolate this K(+) channel by expression cloning in Xenopus oocytes. Injection of renal cortex mRNA into oocytes induced a K(+) conductance, largely inhibited by extracellular Ba(2+) and intracellular taurine. Using this functional test, we isolated from our proximal tubule cDNA library a unique clone, which induced a large K(+) current which was Ba(2+)-, taurine- and glibenclamide-sensitive. Surprisingly, this clone is not a K(+) channel but an adenylate kinase protein (AK3), known to convert NTP+AMP into NDP+ADP (N could be G, I or A). AK3 expression resulted in a large ATP decrease and activation of the whole-cell currents including a previously unknown, endogenous K(+) current. To verify whether ATP decrease was responsible for the current activation, we demonstrated that inhibition of glycolysis greatly reduces oocyte ATP levels and increases an inwardly rectifying K(+) current. The possible involvement of AK in the K(ATP) channel's regulation provides a means of explaining their observed activity in cytosolic environments characterized by high ATP concentrations.

Adenosine Triphosphate↗
PubMed2001

[Pacing therapies for congestive heart failure considering the results of the PATH-CHF study].

Optimized uni- or biventricular pacing therapy improves left ventricular function in 80% of patients (responders) with wide QRS in surface ECG. Immediate improvement could be shown by an increase of LV dP/dt up to 28% and aortic pulse pressure up to 16%. Chronic improvement was documented by prolongation of the 6-minute-walk-test by 60 meters, an improvement of O2 uptake by 23% at exercise, and improvement of quality of life score and NYHA classification. This controlled study has shown for the first time a significant clinical improvement of congestive heart failure by pacing therapy in a selected group of patients. Conventional right ventricular stimulation is insufficient in this group of patients characterized by LBBB. These results support the hypothesis that optimized ventricular stimulation is an effective chronic therapy of congestive heart failure by improvement of left ventricular hemodynamics. Epicardial placement of the left ventricular electrodes in 50 patients was possible without operative and with low (2%) early mortality.

Aged↗
PubMed2001

Mutational analysis of TSC1 and TSC2 genes in gangliogliomas.

Gangliogliomas constitute the most frequent tumour entity in patients with temporal lobe epilepsy. The characteristic histopathological admixture of glial and neuronal elements, the focal nature and their differentiated phenotype and benign biological behaviour suggest an origin from a developmentally compromised or dysplastic precursor lesion. The present study analysed TSC1 and TSC2 genes as potential candidates involved in the pathogenesis of this intriguing neoplasm. Recent data suggest that both genes play a role in cortical differentiation and growth control. DNA sequence analysis of TSC1 and TSC2 was studied in 20 patients with gangliogliomas. Fifteen of these tumours (75%) carried polymorphisms in the TSC2 gene. The frequency of these polymorphisms was significantly increased in intron 4 (12.5%) and exon 41 (15%) compared to control individuals (8.1 and 6.5%, respectively, n = 100). A somatic mutation in intron 32 of the TSC2 gene was encountered in one patient. In the TSC1 gene, seven polymorphisms occurred as a combination of base exchanges in exon 14 and intron 13. No mutations were observed in this gene. Laser microdissection and harvesting of individual neuronal and glial elements identified the intron 32 mutation within the glial portion but not in dysplastic neurones of the tumour. The data demonstrate numerous polymorphisms as well as a novel TSC2 mutation in gangliogliomas from patients with chronic epilepsies. The selective detection of the TSC2 mutation within the glial component of a ganglioglioma suggests that the glioma portion has undergone clonal evolution in this case.

Brain Neoplasms↗
PubMed2001

Isolation of Helicobacter cinaedi from the colon, liver, and mesenteric lymph node of a rhesus monkey with chronic colitis and hepatitis.

On the basis of biochemical, phenotypic, and 16S rRNA analyses, Helicobacter cinaedi was isolated from the colon, liver, and mesenteric lymph nodes of a 2-year-old rhesus monkey with chronic diarrhea. Histologically, the liver had mild to moderate biliary hyperplasia and hypertrophy with periportal inflammation and fibrosis. Colonic and cecal lesions consisted of diffuse chronic inflammation and glandular hyperplasia extending the length of the crypts. This is the first observation of H. cinaedi associated with active hepatitis and colitis in a nonhuman primate.

Animals↗
PubMed2001

Genetic requirements for RAD51- and RAD54-independent break-induced replication repair of a chromosomal double-strand break.

Broken chromosomes can be repaired by several homologous recombination mechanisms, including gene conversion and break-induced replication (BIR). In Saccharomyces cerevisiae, an HO endonuclease-induced double-strand break (DSB) is normally repaired by gene conversion. Previously, we have shown that in the absence of RAD52, repair is nearly absent and diploid cells lose the broken chromosome; however, in cells lacking RAD51, gene conversion is absent but cells can repair the DSB by BIR. We now report that gene conversion is also abolished when RAD54, RAD55, and RAD57 are deleted but BIR occurs, as with rad51Delta cells. DSB-induced gene conversion is not significantly affected when RAD50, RAD59, TID1 (RDH54), SRS2, or SGS1 is deleted. Various double mutations largely eliminate both gene conversion and BIR, including rad51Delta rad50Delta, rad51Delta rad59Delta, and rad54Delta tid1Delta. These results demonstrate that there is a RAD51- and RAD54-independent BIR pathway that requires RAD59, TID1, RAD50, and presumably MRE11 and XRS2. The similar genetic requirements for BIR and telomere maintenance in the absence of telomerase also suggest that these two processes proceed by similar mechanisms.

Chromosomes, Fungal↗
PubMed2001

Left atrial appendage flow in nonrheumatic atrial fibrillation : relationship with pulmonary venous flow and ECG fibrillatory wave amplitude.

OBJECTIVE: This study was conducted (1) to examine the relationship between left atrial appendage (LAA) flow velocity and pulmonary venous flow (PVF) variables during nonrheumatic atrial fibrillation (AF), and (2) to determine whether a reduction in LAA flow is reflected by the fibrillatory wave amplitude on the surface ECG. BACKGROUND: Although LAA Doppler echocardiographic signals provide information regarding the velocity and direction of flow only for a localized narrow sample, systolic PVF represents in part the global left atrial function, mainly relaxation. Controversy exists about whether the amplitude of fibrillatory waves recorded on the surface ECG correlates with LAA flow velocity during AF. MEASUREMENTS AND RESULTS: Thirty-three patients (20 men, 13 women; mean [+/- SD] age, 61 +/- 11 years) with nonrheumatic AF undergoing transthoracic and transesophageal echocardiography were studied. A correlation between LAA flow velocity and systolic PVF variables (peak systolic velocity, R: = 0.450, p = 0.009; velocity-time integral of systolic flow, R = 0.491, p = 0.004; systolic fraction of PVF, R: = 0.627, p < 0.0001) was observed. Patients with a low LAA flow profile (< 25 cm/s) had a reduced systolic PVF. Longer AF duration and the occurrence of moderate mitral regurgitation were related to reduced LAA flow. AF was subdivided into coarse (peak-to-peak fibrillatory amplitude > or = 1 mm) or fine (< 1 mm) in standard ECG lead V1. There was no association between the coarseness of AF and the LAA flow profile. CONCLUSION: In patients with nonrheumatic AF, a reduction in LAA flow velocity correlates with a reduction in systolic PVF. These hemodynamic changes are not reflected by the ECG fibrillatory wave amplitude.

Aged↗
PubMed2000

pH and external Ca(2+) regulation of a small conductance Cl(-) channel in kidney distal tubule.

A single channel characterization of the Cl(-) channels in distal nephron was undertaken using vesicles prepared from plasma membranes of isolated rabbit distal tubules. The presence in this vesicle preparation of ClC-K type Cl(-) channels was first established by immunodetection using an antibody raised against ClC-K isoforms. A ClC-K1 based functional characterization was next performed by investigating the pH and external Ca(2+) regulation of a small conductance Cl(-) channel which we identified previously by channel incorporation experiments. Acidification of the cis (external) solution from pH 7.4 to 6.5 led to a dose-dependent inhibition of the channel open probability P(O). Similarly, changing the trans pH from 7.4 to 6.8 resulted in a 4-fold decrease of the channel P(O) with no effect on the channel conductance. Channel activity also appeared to be regulated by cis (external) Ca(2+) concentration, with a dose-dependent increase in channel activity as a function of the cis Ca(2+) concentration. It is concluded on the basis of these results that the small conductance Cl(-) channel present in rabbit distal tubules is functionally equivalent to the ClC-K1 channel in the rat. In addition, the present work constitutes the first single channel evidence for a chloride channel regulated by external Ca(2+).

Animals↗
PubMed2000

Promotion of Rad51-dependent D-loop formation by yeast recombination factor Rdh54/Tid1.

The first DNA joint formed in homologous recombination processes is a D-loop. Saccharomyces cerevisiae RDH54/TID1-encoded product, a Swi2/Snf2-like factor involved in recombination, is shown here to promote D-loop formation with Rad51 recombinase. Physical interaction between Rdh54 and Rad51 is functionally important because Rdh54 does not enhance the recombinase activity of the Escherichia coli RecA protein. Robust dsDNA-activated ATPase activity in Rdh54 generates unconstrained negative and positive supercoils in DNA. Efficient D-loop formation occurs with even topologically relaxed DNA, suggesting that via specific protein-protein interactions, the negative supercoils produced by Rdh54 are used by Rad51 for making DNA joints.

Adenosine Triphosphatases↗
PubMed2000

Requirement for the SRS2 DNA helicase gene in non-homologous end joining in yeast.

Mitotic cells experience double-strand breaks (DSBs) from both exogenous and endogenous sources. Since unrepaired DSBs can result in genome rearrangements or cell death, cells mobilize multiple pathways to repair the DNA damage. In the yeast Saccharomyces cerevisiae, mitotic cells preferentially use a homologous recombination repair pathway. However, when no significant homology to the DSB ends is available, cells utilize a repair process called non-homologous end joining (NHEJ), which can join ends with no homology through resection to uncover microhomologies of a few nucleotides. Although components of the homologous recombination repair system are also involved in NHEJ, the rejoining does not involve all of the homologous recombination repair genes. The SRS2 DNA helicase has been shown to be required for DSB repair when the homologous single-stranded regions are short. Here it is shown that SRS2 is also required for NHEJ, regardless of the cell mating type. Efficient NHEJ of sticky ends requires the Ku70 and Ku80 proteins and the silencing genes SIR2, SIR3 and SIR4. However, NHEJ of blunt ends, while very inefficient, is not further reduced by mutations in YKU70, SIR2, SIR3, SIR4 or SRS2, suggesting that this rejoining process occurs by a different mechanism.

Adenosine Triphosphatases↗
PubMed2000

Frequency and intensity of crack use as predictors of women's involvement in HIV-related sexual risk behaviors.

Recent trends in the progression of the AIDS epidemic in the United States indicate that women's rates of acquiring HIV are escalating more rapidly than are men's. Consequently, there has been both an increasing interest in and a need for research targeting substance-abusing women's involvement in HIV risk behaviors. In recent years, strong suggestive evidence has arisen to suggest that women who use crack cocaine are at an elevated risk for acquiring HIV, probably as a result of their involvement in high-risk sexual behaviors. The present study is based on a sample of 1723 women from 22 locales around the United States who used crack cocaine at least once during the previous 30 days but who reported never having injected drugs at any point in their lifetime. Women were divided into four groups based on their frequency and intensity of using crack. In subsequent analyses, this grouping was used to predict the extent to which female crack users engage in five sexual risk behavior measures (number of sexual partners, number of drug-injecting sexual partners, number of times having sexual relations while high on alcohol and/or other drugs, number of times trading sex for drugs and/or money, and proportion of all sexual acts involving the use of protection). The data revealed that the women who used crack with the greatest frequency and the greatest intensity were the most heavily involved in risky sexual behaviors. They differed quite sharply from their lower-intensity and/or lower-frequency crack-using counterparts in terms of their HIV risk behavior involvement and in terms of their actual HIV seroprevalence rates.

Acquired Immunodeficiency Syndrome↗
PubMed2000

Arrhythmias in Heart Failure.

Cardiac arrhythmias are very common in the setting of heart failure, with atrial and ventricular arrhythmias often present in the same patient. The risk and the benefit of antiarrhythmic therapies are still a matter of debate. Class I antiarrhythmic drugs should be avoided in patients with heart failure, cardiac ischemia, or previous myocardial infarction. Beta-blocker agents reduce morbidity and decrease mortality in patients suffering from moderate to severe heart failure. Amiodarone may be beneficial in patients with advanced heart failure and increased resting heart rates. This class III drug may be effective to suppress episodes of atrial fibrillation but can also be beneficial in reducing ventricular response by slowing atrioventricular conduction during chronic atrial fibrillation. Implantable cardioverter-defibrillators (ICDs) markedly reduce sudden cardiac death in patients with ventricular tachycardia or ventricular fibrillation. In patients with advanced heart failure, however, the ICD may not markedly extend survival. Recently analyzed data from the Canadian Implantable Defibrillator Study (CIDS), Antiarrhythmics Versus Implantable Defibrillators (AVID) registry, Multicenter Unsustained Tachycardia Trial (MUSTT), and Multicenter Automatic Defibrillator Implantation Trial (MADIT) have consistently shown that it is the sickest patient who benefits the most from ICD therapy. Patients with markedly depressed ejection fraction (<30%), poor New York Heart Association functional class, and advanced age have been identified as those who really need ICD therapy. Studies of implantable cardioverter-defibrillators in patients with moderate to severe heart failure have been launched and will provide necessary answers to the question of whether a reduction in sudden death will translate into a reduction of all-cause mortality. For patients resuscitated from sustained ventricular tachycardia or ventricular fibrillation, an ICD or, in some cases, amiodarone should be considered. Catheter or surgical ablation can be considered for selected patients with ventricular tachycardia.

Journal Article↗
PubMed2000

Age-related differences in the expression of receptors for TGF-beta in human osteoblast-like cells in vitro.

The cell surface expression of receptors for TGF-beta was studied in human osteoblasts derived from femoral trabecular bone of a total of 19 patients aged 2-83 years. All cell populations investigated showed a similar profile of expression of TGF-beta receptors (TbetaR) I, II and III (betaglycan). There were no significant differences in cell differentiation or proliferative behaviour between the age groups. The TGF-beta receptor number per cell significantly increased with age, while the receptor affinity tended to decrease. IGF-I did not influence TbetaR expression in vitro. The results indicate an age-dependent and IGF-I independent increase of osteoblastic TGF-beta receptors in human osteoblast-like cells in vitro.

Adolescent↗