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Biomedical subjects

A Ludwig

Publications and source records attributed to A Ludwig.

At least 73 records · Page 4Linked to original sources
PubMed1999

Subunit expression of the cardiac L-type calcium channel is differentially regulated in diastolic heart failure of the cardiac allograft.

BACKGROUND: Left ventricular diastolic dysfunction is a major cause of cardiac allograft failure. Multimeric L-type calcium channels (alpha1-, alpha2/delta-, and beta-subunits) are essential for excitation/contraction coupling in the heart. Their gene expression was studied in allografts that developed diastolic heart failure. METHODS AND RESULTS: mRNA levels of calcium channel subunits were measured by competitive reverse transcriptase-polymerase chain reaction in microbiopsy samples from the interventricular septum. Size and tissue variabilities between biopsy samples were assessed by determination of cardiac calsequestrin mRNA levels. In the cardiac allografts studied, mRNA levels in microbiopsy samples were considered to represent left ventricular gene expression, because septal and left ventricular gene expression in Northern blots was equivalent, and left ventricles contracted homogeneously. Biopsy samples (n=72) were taken from allografts with normal left ventricular end-diastolic pressure (LVEDP; 8 to 13 mm Hg; n=30), moderately elevated LVEDP (14 to 18 mm Hg; n=26), and elevated LVEDP (19 to 28 mm Hg; n=16). Increased LVEDP was related to slowed diastolic relaxation determined by the time constant tau (r2=0.86), whereas systolic performance (dP/dt; ejection fraction) was preserved. With increasing LVEDP, mRNA levels of the pore-forming alpha1c-subunit (n=15) and of the regulatory alpha2/delta-subunit (n=17) remained unchanged but decreased exponentially (r2=-0.83) for the regulatory beta-subunit (n=40). Compared with cardiac allografts with normal LVEDP (n=15), beta-subunit mRNA level was reduced by 75% at elevated LVEDP (n=9; P=0.012). In an explanted, diastolically failing cardiac allograft, beta-subunit expression was reduced correspondingly by 72% and 76% on the mRNA level in septal and left ventricular myocardium and by 80% on the protein level. CONCLUSIONS: The downregulated expression of the calcium channel beta-subunit might contribute to altered calcium handling in diastolically failing cardiac allografts.

Adult↗
PubMed1999

Structural analysis of a plant sucrose carrier using monoclonal antibodies and bacteriophage lambda surface display.

Monoclonal antibodies were raised and selected against recombinant Plantago major PmSUC2 sucrose carrier protein. Epitopes of two monoclonal antibodies (PS2-1A2 and PS2-4D4) were mapped using N-terminally truncated PmSUC2 proteins and a lambda library displaying random PmSUC2 peptides. PS2-1A2 recognizes an octapeptide close to the N-terminus of PmSUC2, PS2-4D4 binds to a decapeptide at the very C-terminus. Analyses of antibody binding to yeast protoplasts with functionally active, tagged PmSUC2 protein revealed that both epitopes are located in cytoplasmic domains of PmSUC2. These results support a model for plant sucrose transporters containing 12 transmembrane helices with the N-terminus and the C-terminus on the cytoplasmic side of the plasma membrane.

Amino Acid Sequence↗
PubMed1999

Selective loss of cone function in mice lacking the cyclic nucleotide-gated channel CNG3.

Two types of photoreceptors, rods and cones, coexist in the vertebrate retina. An in-depth analysis of the retinal circuitry that transmits rod and cone signals has been hampered by the presence of intimate physical and functional connections between rod and cone pathways. By deleting the cyclic nucleotide-gated channel CNG3 we have generated a mouse lacking any cone-mediated photoresponse. In contrast, the rod pathway is completely intact in CNG3-deficient mice. The functional loss of cone function correlates with a progressive degeneration of cone photoreceptors but not of other retinal cell types. CNG3-deficient mice provide an animal model to dissect unequivocally the contribution of rod and cone pathways for normal retinal function.

Animals↗
PubMed1999

Two pacemaker channels from human heart with profoundly different activation kinetics.

Cardiac pacemaking is produced by the slow diastolic depolarization phase of the action potential. The hyperpolarization-activated cation current (If) forms an important part of the pacemaker depolarization and consists of two kinetic components (fast and slow). Recently, three full-length cDNAs encoding hyperpolarization-activated and cyclic nucleotide-gated cation channels (HCN1-3) have been cloned from mouse brain. To elucidate the molecular identity of cardiac pacemaker channels, we screened a human heart cDNA library using a highly conserved neuronal HCN channel segment and identified two cDNAs encoding HCN channels. The hHCN2 cDNA codes for a protein of 889 amino acids. The HCN2 gene is localized on human chromosome 19p13.3 and contains eight exons spanning approximately 27 kb. The second cDNA, designated hHCN4, codes for a protein of 1203 amino acids. Northern blot and PCR analyses showed that both hHCN2 and hHCN4 are expressed in heart ventricle and atrium. When expressed in HEK 293 cells, either cDNA gives rise to hyperpolarization-activated cation currents with the hallmark features of native If. hHCN2 and hHCN4 currents differ profoundly from each other in their activation kinetics, being fast and slow, respectively. We thus conclude that hHCN2 and hHCN4 may underlie the fast and slow component of cardiac If, respectively.

Biological Clocks↗
PubMed1999

[Roentgenologic, endoscopic and ultrasound evaluation of the maxillary sinus after sinus lift with simultaneous endosseous implantation].

X-ray, ultrasound, and endoscopy were used in follow-up after sinus floor augmentation. In 23 out of 63 patients, healing was uneventful. Water's view revealed opacification of the maxillary sinus 1 week postoperatively in 40 patients, and opacification persisted in four patients. In these patients, endoscopy showed inflammatory reactions of the mucosa. Ultrasound proved to be a valuable tool in follow-up. Sinusitis occurred in three patients and was due to migration of bone chips in two of these. Out of 132 inserted implants, eight were lost during the healing period and three more during the loading period.

Alveolar Bone Loss↗
PubMed1999

NH4+ conductance in Xenopus laevis oocytes.II. Effect Of hypoosmolality.

Superfusing Xenopus laevis oocytes with NH4Cl (10 mmol/l, pH 7.5) resulted in an inward current at a clamp potential of -70 mV. In paired experiments (n=22), the NH4Cl-induced peak current was -293+/-94 nA, under control conditions (osmolality: 240 mosmol/kg), and rose to -523+/-196 nA when osmolality was reduced to 144 mosmol/kg. In parallel with the rise in NH4Cl-induced inward current, membrane conductance at -70 mV doubled and the zero-current potential changed from +3.3+/-9.4 mV to -22.0+/-8.0 mV (n=22) in the presence of NH4Cl during exposure to a hypoosmolar solution. In the absence of NH4Cl, oocytes responded to hypoosmolality with a shift in zero-current potential to more negative values and an increased conductance which became partially sensitive to isosorbiddinitrate (ISDN), suggesting the activation of a volume-sensitive K+ channel. Membrane conductance in the presence of NH4Cl was decreased by ISDN to similar extents under isoosmolal and hypoosmolal conditions, indicating that NH4+ enters the oocytes through a volume-sensitive conductance separate from the ISDN-sensitive K+ channel.

Ammonium Chloride↗
PubMed1999

Influence of the physico-chemical properties of ophthalmic viscolysers on the weight of drops dispensed from a flexible dropper bottle.

The present study investigated the influence of the rheological behaviour, the viscoelasticity and surface tension of various viscolysers on the weight of drops dispensed from a commercially available flexible dropper bottle. Furthermore, the effect of the concentration and molecular weight of some viscolysers and the angle at which the dropper bottle is held, were studied. Up to a value of 25 mPa x s, the viscosity and the rheological behaviour of the solution had no significant influence on the drop weight under conditions simulating patient manipulation. The lower the dynamic surface tension of the solution, however, the lower the weight of drops delivered. The dispensing angle (90 or 45 degrees) of the dropper bottle, on the other hand, had an impact on the weight of drops dispensed.

Chemical Phenomena↗
PubMed1999

Characterization of the C-terminal domain essential for toxic activity of adenylate cyclase toxin.

Adenylate cyclase toxin (CyaA) of Bordetella pertussis belongs to the RTX family of toxins. These toxins are characterized by a series of glycine- and aspartaterich nonapeptide repeats located at the C-terminal half of the toxin molecules. For activity, RTX toxins require Ca2+, which is bound through the repeat region. Here, we identified a stretch of 15 amino acids (block A) that is located C-terminally to the repeat and is essential for the toxic activity of CyaA. Block A is required for the insertion of CyaA into the plasma membranes of host cells. Mixing of a short polypeptide composed of block A and eight Ca2+ binding repeats with a mutant of CyaA lacking block A restores toxic activity fully. This in vitro interpolypeptide complementation is achieved only when block A is present together with the Ca2+ binding repeats on the same polypeptide. Neither a short polypeptide composed of block A only nor a polypeptide consisting of eight Ca2+ binding repeats, or a mixture of these two polypeptides, complement toxic activity. It is suggested that functional complementation occurs because of binding between the Ca2+ binding repeats of the short C-terminal polypeptide and the Ca2+ binding repeats of the CyaA mutant lacking block A.

Adenylate Cyclase Toxin↗
PubMed1999

Analysis of the SlyA-controlled expression, subcellular localization and pore-forming activity of a 34 kDa haemolysin (ClyA) from Escherichia coli K-12.

Escherichia coli K-12 harbours a chromosomal gene, clyA (sheA, hlyE), that encodes a haemolytic 34 kDa protein. Recombinant E. coli overexpressing the cloned clyA gene accumulated this haemolysin in the periplasm and released only very small amounts of it into the external medium. The secretion of ClyA was confined to the log phase and paralleled by the partial release of several other periplasmic proteins. Sequencing of ClyA revealed the translational start point of the clyA gene and demonstrated that the clyA gene product is not N-terminally processed during transport. The transcription of clyA from its native promoter region was positively controlled by SlyA, a regulatory protein found in E. coli, Salmonella typhimurium and other Enterobacteriaceae. SlyA-controlled transcription started predominantly 72 bp upstream from clyA, as shown by primer extension. The corresponding putative promoter contains an unusual -10 sequence (TATGAAT) that is separated from a conventional -35 sequence by a GC-rich spacer. Site-directed deletion of the G in the -10 sequence abrogated the SlyA requirement for strong ClyA production, whereas a reduction in the G + C content of the spacer diminished the capability of SlyA to activate the clyA expression. Osmotic protection assays and lipid bilayer experiments suggested that ClyA forms stable, moderately cation-selective transmembrane pores that have a diameter of about 2.5-3 nm.

Bacterial Proteins↗
PubMed1999

[Treatment outcome after surgical arthrodesis].

Different results are reported following total wrist fusion. We performed 64 total wrist fusions due to posttraumatic or degenerative arthrosis of the wrist including Kienböck's disease. Clinical outcome was evaluated using the DASH-questionnaire. The mean DASH-function/symptom score was 45.6 points (0 points representing the best possible results and 100 points representing the worst possible result). In addition, 35 patients of this group were reexamined clinically and radiologically using a modified traditional wrist score. The preliminary results of the traditional wrist score and the DASH-score demonstrated a significant correlation (r = -0.71; p < 0.001) indicating the validity of the DASH-score. In conclusion, this study shows that wrist fusion results in significant pain reduction and improvement of function. However, complete pain relief cannot be expected for the majority of patients. The new AO wrist fusion plate is used in our standard technique of wrist fusion. In a further study, we will investigate the outcome of total wrist fusion in comparison with limited wrist fusion using the DASH-questionnaire and the wrist score.

Adult↗
PubMed1999

Structure and function of cardiac pacemaker channels.

Cardiac pacemaking is controlled by a mixed Na(+)/K(+) current named I(f), which is activated by hyperpolarized membrane potentials. Recently, a family of hyperpolarization-activated cyclic nucleotide-gated cation (HCN) channels has been cloned. The members of this family exhibit the general features of I(f) channels. This review describes the molecular diversity of the HCN channel family and the structural determinants of channel function including activation by voltage, modulation by cyclic nucleotides and ion permeation. The relationships between cloned HCN channel types and native cardiac I(f) currents are explored.

Amino Acid Sequence↗
PubMed1998

Bacteriophage lambda surface display of a bacterial biotin acceptor domain reveals the minimal peptide size required for biotinylation.

Phage display is a powerful technique for identifying specific ligands to a given target. In this work random peptides derived from the biotin accepting domain of the Klebsiella pneumoniae oxaloacetate decarboxylase were displayed on bacteriophage lambda heads to determine the minimal sequence length that is necessary to effect biotinylation in vivo. Phages with a functional biotinylation domain were identified after affinity purification with immobilised avidin. All biotinylated phages isolated this way were found to have a sequence of 66 amino acids from the parental protein in common. This minimal biotinylation domain is fully functional as a biotin acceptor and more resistant to proteolytic attack compared to domains of larger size derived from the same protein. The data present the first example of a posttranslational protein modification analysed in a phage display system. Moreover, a biotin domain of reduced size and improved stability was identified, that should be superior to the larger parental protein as a tag to generate biotinylated fusion proteins.

Amino Acid Sequence↗
PubMed1998

A family of hyperpolarization-activated mammalian cation channels.

Pacemaker activity of spontaneously active neurons and heart cells is controlled by a depolarizing, mixed Na+/K+ current, named Ih (or I(f) in the sinoatrial node of the heart). This current is activated on hyperpolarization of the plasma membrane. In addition to depolarizing pacemaker cells, Ih is involved in determining the resting membrane potential of neurons and provides a mechanism to limit hyperpolarizing currents in these cells. Hormones and neurotransmitters that induce a rise in cyclic AMP levels increase Ih by a mechanism that is independent of protein phosphorylation, and which involves direct binding of the cyclic nucleotide to the channel that mediates Ih. Here we report the molecular cloning and functional expression of the gene encoding a hyperpolarization-activated cation channel (HAC1) that is present in brain and heart. This channel exhibits the general properties of Ih channels. We have also identified full-length sequences of two related channels, HAC2 and HAC3, that are specifically expressed in the brain, indicating the existence of a family of hyperpolarization-activated cation channels.

Amino Acid Sequence↗
PubMed1998

Cyclic nucleotide-gated channels--mediators of NO:cGMP-regulated processes.

Cyclic nucleotide-gated (CNG) channels represent one of the three known cellular receptor classes for cGMP. Activation of CNG channels by binding of cyclic nucleotides to a site in the C-terminus results in opening of the channel pore, entry of Ca2+ into the cell and subsequent induction of Ca2+-dependent processes. In this review we will summarize new data on the complex molecular structure and the activation mechanism of CNG channels. In addition, we will discuss the role of CNG channels as mediators of NO:cGMP-dependent cellular processes.

Animals↗
PubMed1998

New perspectives in head and neck sonography by signal-enhanced color Doppler sonography.

Ultrasound contrast agent is used in color Doppler flow imaging for signal enhancement in perfused vessels. We present our experience with its use in the head and neck area and the results obtained. Up until now, 30 patients with carcinomas of the oral cavity or the maxillary sinus, tumors of the mandible and metastatic or inflammatory lymph nodes have been examined. Conventional B-scan sonography was supplemented by non-contrast color Doppler flow imaging. Depending on the indication, 2.5 g Levovist in bolus or 4 g fractionated was injected intravenously in a concentration of 300 or 400 mg/ml. The administration of the contrast agent was tolerated by all patients without any side effects and in all cases led to a remarkable enhancement of the Doppler signals. About 15 to 30 s after injection, an enhancement in perfused vessels was detected. The fractioned injection of 4 g led to a lengthening of signal enhancement up to more than 10 min and to the possibility of examining more parts with a single application of contrast agent. In 64% of the lymph nodes, vessels could only be identified with the administration of Levovist. The general vessel topography could be better evaluated in 83% of the cases. The lymph-node-supplying vessels were identified in 8 of 11 patients after the injection of contrast media. Additional information, which was gained in 17 patients, increased the certainty of diagnosis or of the therapeutic concept. In three cases, the examinations with the signal enhancer resulted in a change in therapy. By applying signal enhancer in color Doppler sonography the fields of examination in the head and neck areas can be expanded.

Blood Flow Velocity↗
PubMed1998

The influence of penetration enhancers on the volume instilled of eye drops.

The influence of the physicochemical properties of various penetration enhancers on the weight of drops dispensed from flexible plastic dropper bottles was examined. Two dropper tips with a different design were compared and the dropper bottle was held in the upright position (90 degrees angle) or at a 45 degrees angle. These two angles were chosen to simulate the manipulation of an eye dropper bottle by the patient. The surface tension of the penetration enhancer solutions was determined using the dynamic drop volume method. The dynamic surface tension values ranged from 65 to 30 mN/m. The lower the surface tension of the solution, the lower the weight of the drop delivered. Both the design of the dropper tip and the manipulation technique of the dropper bottle had a moderate to important influence on the drop weight. The relationship between the surface tension of the penetration enhancer solution instilled and the comfort of the patient was evaluated by an acceptability test based on answering a questionnaire. Penetration enhancers can be used to reduce the drop size of conventional ophthalmic solutions on condition that they do not elicit local irritation.

Chemistry, Pharmaceutical↗