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Biomedical subjects

M Pfister

Publications and source records attributed to M Pfister.

At least 55 records · Page 3Linked to original sources
PubMed1998

Cellular/molecular control of renal Na/Pi-cotransport.

A type II Na/Pi-cotransporter located in the brush border membrane is the rate limiting and physiologically regulated step in proximal tubular phosphate (Pi) reabsorption. In states of altered Pi-reabsorption [for example, in response to parathyroid hormone (PTH) and to altered dietary intake of Pi or as a consequence of genetic abnormalities], brush border expression of the type II Na/Pi-cotransporter is accordingly modified. PTH initiates a regulatory cascade leading to membrane retrieval, followed by lysosomal degradation of this transporter; recovery from inhibition requires its de novo synthesis. Pi-deprivation leads to an increased brush border expression of transporters that does not appear to require de novo synthesis in the short term. Pi-overload leads to membrane retrieval and degradation of transporters. Finally, in animals with genetically altered Pi-handling (Hyp; Gy) the brush border membrane expression of the type II Na/Pi-cotransporter is also reduced, suggesting that a genetically altered protein (such as PEX in Hyp) controls the expression of this transporter.

Animals↗
PubMed1998

[Painless, red-violet skin lesions during immunosuppression].

A patient with painless, bluish-red skin lesions under immunosuppressive treatment for kidney transplantation is presented. The clinical and histological diagnosis was Kaposi's sarcoma. This is a rare but serious complication in the immunocompromised patient. Human Herpes virus 8 (HHV 8) was recently found in the lesions from patients with Kaposi's sarcoma. This supports the important role of immunosuppression in the development of this tumor. Therapy consists of reduction or stopping of the immunosuppressive drugs which is usually followed by reduction in tumor mass. Local skin tumors can be treated with irradiation or laser therapy. In the case of lesions of visceral organs chemotherapeutic regimens consisting of vinicristine/bleomycin are indicated. New strategies aim to reduce the virus load with antiviral drugs or to inhibit the angiogenesis of this highly vascularized tumor.

Biopsy↗
PubMed1997

Mutation of amino acids 39-44 of human CD14 abrogates binding of lipopolysaccharide and Escherichia coli.

As a key receptor for lipopolysaccharide (LPS) on the surface of monocytes and macrophages, the CD14 molecule is primarily involved in non-specific host defense mechanisms against gram-negative bacteria. To delineate the structural basis of LPS binding, 23 mutants in the N-terminal 152 amino acids of human CD14 were generated and stably transfected into CHO cells. In each mutant, a block of five amino acids was substituted by alanine. Reactivity of the mutants with anti-CD14 mAbs, and their ability to interact with LPS and Escherichia coli were tested. 4 of 21 expressed CD14 mutants, ([Ala9-Ala13]CD14, [Ala39-Ala41, Ala43, Ala44]CD14, [Ala51-Ala55]CD14 and [Ala57, Ala59, Ala61-Ala63]CD14), are not recognized by anti-CD14 mAbs that interfere with the binding of LPS to human monocytes. However, only [Ala39-Ala41, Ala43, Ala44]CD14 is unable to react with fluorescein-isothiocyanate-labeled LPS or with FITC-labeled E. coli (055:B5). In addition, [Ala39-Ala4l, Ala43, Ala44]CD14 does not mediate LPS (E. coli 055:B5; 10 ng/ml)-induced translocation of nuclear factor kappaB in CHO-cell transfectants. The results indicate that the region between amino acids 39 and 44 forms an essential part of the LPS-binding site of human CD14.

Amino Acid Sequence↗
PubMed1997

Selective in vitro removal of anti-A antibodies by adsorption on encapsulated erythrocyte-ghosts.

Large volume plasma exchanges are used for the removal of anti-A or anti-B antibodies from the plasma of patients undergoing transplantation from donors with major ABO incompatibility. Previous works suggest that solid-phase immunoadsorption can be substituted for plasma exchange in situations where antigens can be purified and immobilized on columns through which plasma is percolated. However, the preparation of purified antigens of the ABO system is large quantities is laborious and requires the use of considerable blood volumes. Studies were therefore undertaken to determine the feasibility of an original immunoadsorbent based on porous microparticles prepared by a water/oil/water emulsification-solvent evaporation method, within which erythrocytes-ghosts carrying blood group antigens were entrapped. The decrease of the antibody hemagglutinating titre after adsorption onto encapsulated ghosts suggests that antibodies can cross the polymeric membrane and bind to the antigens. This original approach of using encapsulated antigens for the batchwise removal of antibodies could be extended to affinity chromatography, and immunoadsorption therapy with a chromatographic column linked to an extracorporeal circulation could be considered.

ABO Blood-Group System↗
PubMed1997

[In vivo cochleoscopy through the round window].

The overall aim of the present investigation was to develop a technique for endoscopic investigation of the cochlea. In the experiments reported here, the possible effect of the endoscope-called the "cochleoscope"-on the electrophysiology of the cochlea was investigated by recording the cochlear action potential (CAP) threshold tuning curve from (0.1-34 kHz). The dorsolateral bulla of anesthesized guinea pigs (with ketamine 60 mg/kg and Rompun 12 mg/kg) was opened, after which the cochleoscope was introduced under micromanipulator control through the round window membrane. Three cochleoscopes were used and had diameters of 0.29 mm, 0.7 mm and 0.89 mm, respectively, containing 2000, 3000 and 3000 fibers each. Experiments in 7 animals showed that the cochleoscope did not influence CAP thresholds. Although the present resolution of the endoscopes is limited, the basilar membrane can be clearly distinguished from the osseous spiral lamina. It is anticipated that improved resolution will allow the cochleoscope to be used for diagnostic purposes in cases of sensorineural hearing loss.

Animals↗
PubMed1996

[ACE-inhibitors in acute heart infarct].

The use of ACE-inhibitors in heart failure has been established over the past years. Their use is of uncertain value in the early phases of myocardial infarction, where they are supposed to prevent left ventricular dilatation. More recent studies (ISIS-4, GISSI-3) have tested early treatment by ACE-inhibitors in the acute phase of myocardial infarction. On one hand, it was possible to disprove reservations about risks (hypotension)n in a large cohort; on the other hand, a further reduction of mortality in hospitalized patients by 7% has been shown, corresponding to five patient lives saved for 1000 treated patients. Thus, after institution of the customary therapy of myocardial infarction (inhibitor of platelet aggregation, thrombolysis, beta-blocker) and after exclusion of specific contraindications (hypotension < 100 mmHg, renal failure) ACE-inhibitors could be administered in the acute phase of myocardial infarction. An analysis of the results from these large trials will show whether ACE-inhibitors may benefit groups of patients at particular risks (Killip > 1, age > 70 years, preceding renal failure) noticeably. ACE-inhibitors remain the treatment of choice in patients with developing left ventricular failure.

Acute Disease↗
PubMed1996

The myeloid differentiation antigen CD14 is N- and O-glycosylated. Contribution of N-linked glycosylation to different soluble CD14 isoforms.

The myeloid differentiation antigen CD14 acts as the major receptor for bacterial lipopolysaccharide (LPS). A soluble form of the protein (sCD14) is present in human serum which functions as a soluble LPS receptor. We have compared the isoform patterns of soluble CD14 derived from human serum and of the recombinant proteins produced by CHO cells transfected with either the wild-type CD14 gene or with a cDNA coding for a truncated protein which lacks the C-terminal 21 amino acids [sCD14-(1-335)-peptide]. Using SDS/PAGE, two dominant isoforms (53 and 50 kDa) and two minor forms (46 and 43 kDa) can be detected in serum as well as in the supernatants of both transfectants. sCD14 is a glycoprotein which carries N- and O-linked carbohydrates. The different isoforms of sCD14-(1-335)-peptide are due to differences in the content of N-linked sugars. However after the removal of N- and O-linked carbohydrates from serum- and CHO-derived wild-type proteins, two isoforms are still present. These results indicate that N-linked glycosylation contributes to but does not fully explain the different forms of soluble CD14. We further examined whether the mutation of individual N-linked glycosylation sites influences the expression of membrane-bound and soluble CD14 forms and the ability of the membrane-bound molecule to bind LPS. As with the wild-type proteins, the different isoforms of the soluble mutants are partially due to differences in N-linked glycosylation. A truncated mutant which lacks the two N-terminal glycosylation sites {[Asp18, Asp132]CD14-(1-335)peptide} does not give rise to multiple forms on SDS gels. Like CD14-(1-335)-peptide, this mutant is not expressed on the cell surface suggesting that a smaller isoform present in the wild-type preparations results from proteolytic cleavage of the membrane-bound molecule. N-linked carbohydrates do not seem to be important for the binding of LPS to membrane-bound CD14.

Animals↗
PubMed1996

Extracellular adenosine levels in neostriatum and hippocampus during rest and activity periods of rats.

Adenosine is an inhibitory modulator in the mammalian brain with a possible role in sleep regulation, which is mainly indicated by pharmacological studies showing that adenosine or its analogs can induce sedation and sleep, whereas adenosine antagonists, like caffeine and theophylline, are potent behavioral and neuronal stimulants. In contrast to these pharmacological findings, data on endogenous adenosine in relation to sleep and waking are sparse. Therefore, we have now used in vivo microdialysis to investigate the extracellular levels of adenosine in the neostriatum and hippocampus of freely moving rats. Adenosine was monitored over a time course of 24 h, during which the animals were exposed to a 12 h day/night rhythm with lights-off from 19.00 to 07.00. In this lights-off period, i.e. the rats' active period, the maximal levels of neostriatal and hippocampal extracellular adenosine were higher than during the lights-on period. In contrast to the neostriatum, extracellular levels of hippocampal adenosine tended to increase towards the end of the lights-off period, reaching its maximal level at 07.00, and decreasing again within the following hour. The changes of hippocampal adenosine levels were related to behavior, since significant increases in "sleep-like" behavior, as well as decreases in overall movements and consummatory behavior, were observed when adenosine levels had reached their maxima in the hippocampus; no such relationship was found with respect to the neostriatum. These results are in keeping with a role of endogenous adenosine in the regulation of sleep and wakefulness, and point to a specific role of adenosine in the hippocampus. They also raise the possibility that adenosine may be involved in different behavioral processes dependent on the area of the brain, as well as the type of adenosine receptor involved. Finally, given the known evidence for neuroprotective actions of adenosine, its accumulation in the hippocampus as a function of behavioral activity may serve to prevent or repair the neural degenerative consequences of such activity. It is proposed that adenosine's sleep-promoting effects result from its signalling to cease behavioral activity in order to prevent excessive activity-related changes, and thus allow other restorative sleep-related processes to take over.

Adenosine↗
PubMed1996

Tissue homeostatic role of naturally occurring anti-band 3 antibodies.

Self antigens exposed to the immune system constitutively or in the process of tissue homeostasis may stimulate a TH2 type immunity giving rise to low titer, low affinity naturally occurring antibodies which are involved in actively maintaining peripheral tolerance to self and in tissue homeostatic clearance processes. In reviewing the tissue homeostatic aspect of naturally occurring antibodies to band 3 protein of the human erythrocyte membrane, we address crucial issues of how these and other types of naturally occurring antibodies (NAb) (eg. anti-spectrin NAb) gain functionality and how this can induce opsonization by complement C3b under physiological conditions. Exoplasmic, chemical cross-linking of band 3 protein is sufficient to increase specific anti-band 3 binding under physiological conditions. Formation of oligomers following this non-oxidative cross-linking protocol disfavors a recognition mechanism involving exposure of a neoantigen. New data on NAb binding to erythrocytes further demonstrates that specific binding of any low affinity NAb can only be determined in the presence of whole human IgG and physiological ionic strength, where competition of the predominantly positively charged NAb for binding to the negatively charged cell surface is high. Hence, specific and physiologically relevant binding of low affinity NAb is gained by bivalent binding and suppression of exclusive charge-charge interactions by other NAb sharing the range of pl values. Therefore, many investigations on NAb/cell interactions which have been carried out in the absence of whole IgG have yielded controversial data.

Anion Exchange Protein 1, Erythrocyte↗
PubMed1995

Immunoadsorption procedure as a potential method for the specific beta 2-microglobulin removal from plasma of patients with chronic renal failure.

beta 2-Microglobulin (beta 2-M), which accumulates in the plasma of patients undergoing long-term dialysis, has been identified as the principal precursor protein of amyloid fibrils in dialysis-related amyloidosis. As no specific treatment for this affection has been yet established, an extracorporeal immunoadsorption procedure appears to be an attractive therapeutic approach to remove beta 2-M. Several murine monoclonal antibodies to human beta 2-M were developed and compared as affinity ligands. One of them was selected on the basis of its specificity and adsorption capacity. In order to achieve maximum efficiency in protein removal, different parameters of the procedure were studied and optimized: effect of antibody coupling density, determination of maximum adsorption capacity of the immunoadsorbents and influence of antigen concentration and of flow-rate on antigen capture efficiency. The conditions of regeneration of immunoaffinity sorbents were also investigated to allow their multiple use without loss of adsorption capacity. The results show the validity of the proposed technique in removing beta-M from plasma of patients with chronic renal failure.

Antibodies, Monoclonal↗
PubMed1995

HPLC analysis of tonka bean extracts.

Based on the results of GC-MS analysis, an HPLC procedure was developed for the determination of coumarin, dihydrocoumarin, melilotic acid (o-dihydrocoumaric acid), methyl melilotate, ethyl melilotate, 5-hydroxymethylfurfural and o-coumaric acid which are characteristic compounds of tonka beans. The presence of melilotic acid and ethyl melilotate in tonka beans has not been reported previously. Following HPLC analysis of tonka bean extracts produced in the laboratory and one sample of commercially available tonka bean absolute, evidence was provided that solvents used for production are decisive for the kind and amount of the compounds detected.

Chromatography, High Pressure Liquid↗
PubMed1994

Substance P decreases extracellular concentrations of acetylcholine in neostriatum and nucleus accumbens in vivo: possible relevance for the central processing of reward and aversion.

It has been shown that peripherally administered substance P has reinforcing effects and can promote functional recovery after unilateral partial lesion of the nigrostriatal system. Furthermore, peripheral injection of substance P induces an increase in extracellular striatal dopamine. To obtain further information about the central mechanisms of these properties we used the in vivo microdialysis technique to investigate changes in the extracellular concentrations of acetylcholine in neostriatum and nucleus accumbens after intraperitoneal (i.p.) administration of substance P or vehicle in freely moving rats. The i.p. administration of 50 micrograms/kg substance P induced a steady, long-lasting decrease in the extracellular concentrations of acetylcholine in neostriatum, while no changes were observed in the nucleus accumbens. In comparison, substance P in a dose of 250 micrograms/kg i.p. acutely decreased the extracellular levels of acetylcholine in both nuclei. Interestingly, after the administration of vehicle, an acute increase in acetylcholine levels was observed in the nucleus accumbens, but not in the neostriatum. This effect did not occur after the injection of substance P indicating that the neurokinin blocked the increase in acetylcholine levels induced by the vehicle injection. These effects of substance P on striatal acetylcholine are discussed with respect to their relationship with dopamine and endogenous opiates, and with respect to the functional role of substance P, such as in reward, aversion, motor activity, and functional recovery.

Acetylcholine↗
PubMed1994

Frequency response of mature guinea-pig outer hair cells to stereociliary displacement.

Outer hair cells (OHC) were isolated from the apical two turns of the guinea-pig cochlea and their hair-bundle stimulated mechanically by a glass probe. In accordance with in vivo data (Dallos, 1985), the resting membrane potential was typically -64 mV (N = 200). The maximum amplitudes of the receptor potentials were between 0.4 and 5.2 mV peak-to-peak, with mean of 1.5 mV +/- 0.9 mV (N = 81). The sensitivity was 0.015 mV/nm or 2 mV/deg. The frequency response of the receptor potential followed a first order low-pass filter characteristic with a corner frequency of about 63 Hz. For frequencies up to at least 1.6 kHz, the frequency response of mechanoelectrical transduction was dominated by the electrical input impedance of the cell. The presence of a single time constant in the voltage response to stereociliary deflection implies that the frequency response of mechanoelectrical transduction far exceeds that of the electrical input impedance of the cell; its time constant must be faster than 100 microseconds. Under in vivo conditions, OHC should be capable of providing a sufficiently large receptor potential to supply enough energy for electromechanical feedback.

Acoustic Stimulation↗
PubMed1994

Different effects of scopolamine on extracellular acetylcholine levels in neostriatum and nucleus accumbens measured in vivo: possible interaction with aversive stimulation.

The in vivo microdialysis technique was used to measure extracellular concentrations of acetylcholine (ACh) in the neostriatum (NS) and nucleus accumbens (NAc) of freely moving rats after intraperitoneal administration of the muscarinic receptor antagonist scopolamine (0.5 mg/kg) or vehicle. Simultaneously, behavior was monitored. The administration of scopolamine induced an increase in extracellular ACh levels in the NS, which reached a maximum of about 185% within one hour after injection and returned to baseline values about three hours after injection. In the NAc, an increase of similar time-course was observed; however, this increase reached a maximum of 250%, which was significantly higher than the one observed in NS. These changes in ACh levels were accompanied by enhanced locomotion, rearing and grooming; however, the behavioral changes were of shorter time-course than those of extracellular ACh. The injection of vehicle did not affect ACh levels in NS, but induced a significant increase (60%) in the NAc. The levels of behavioral activity after vehicle injection did not differ from pre-injection levels. These results suggest, that the cholinergic systems in the NAc and NS are differently affected by peripheral administration of both scopolamine and vehicle. The differential effects of scopolamine in NS and NAc could reflect pharmacodynamic differences between these two striatal brain areas, perhaps due to a higher density of cholinergic interneurons or muscarinic autoreceptors in the NAc in comparison to the NS. However, the increase of extracellular ACh observed after vehicle injection suggests that factors such as aversive stimulation through the injection procedure can increase ACh release in the NAc and that such a mechanism can interact within the action of scopolamine. Thus, the stronger action of scopolamine on extracellular ACh in the NAc might be an additive effect of the drug with that of the injection procedure.

Acetylcholine↗
PubMed1993

[Mechanical stimulation of isolated outer hair cells as a test system. Inhibition of transduction by streptomycin treatment].

Deflection of the hair bundle of isolated outer hair cells from the guinea pig cochlea can induce a receptor potential. Outer hair cells from the third and fourth turns of the guinea pig cochlea were isolated according to the method described by Zenner et al. Cells were maintained in Hank's balanced salt solution at room temperature. The whole cell potential was measured by the patch-clamp technique with soda glass capillaries (resistance 3-5 M omega) filled with KCl-Ringer solution. After compensation for the junction potential the stable resting potential of 46 cells was -63 mV +/- 5 mV. The hair bundle was deflected sinusoidally, with amplitudes ranging from 6 degrees to a maximum of 31 degrees in the positive direction (i.e., in the direction of the longest stereocilium). The stimulus was a piezo-driven glass capillary with an opening diameter of 5 microns. This mechanical stimulation induced in 33% of all stimulated cells (n = 46) a receptor potential response of 2.1 +/- 1.4 mV (maximally 5.5 mV). Deflection of the hair bundle in the opposite direction led to no change in the membrane potential, i.e. the cells were not hyperpolarized (minimal resolution 0.5 mV). Since the resting potential of the cells was more positive than the potassium equilibrium potential under our experimental conditions, the receptor current was most likely mediated by an influx of Na+ ions into the cell. The receptor potential response could be completely and reversibly blocked by the addition of dihydro-streptomycin.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Monoclonal antibodies against human plasma protein C and their uses for immunoaffinity chromatography.

Human protein C, isolated by conventional multistep methods, was used for immunization of mice. Monoclonal antibodies were prepared and screening of antibodies to human protein C was achieved using an immunoblotting technique. Five monoclonal anti-protein C antibodies were compared as affinity ligands. Different parameters were studied (adsorption capacity, specificity of adsorption, possibility of desorption under mild conditions) and two antibodies were selected. One antibody allows preparation of highly purified protein C in a single-step procedure from a fraction of plasma containing high levels of coagulation factors whereas the other can be used for preparation of protein C deficient plasma.

Antibodies, Monoclonal↗