Biomedical subjects

A Schmid

Publications and source records attributed to A Schmid.

At least 127 records · Page 7Linked to original sources

PubMed1996

[Coronary circulation and metabolic function in endurance trained paraplegics].

OBJECTIVE: To determine the effect of physical activity on pulmonary, cardiovascular and metabolic activity in paraplegics. PATIENTS AND METHODS: Eight male paraplegics (average age 35.7 [range 25-47] years) had been selected from a pool of training members of the German Sport Union for the Disabled. They performed graded arm crank training for 8.3 +/- 3.1 h/week. Left ventricular volume (LVV), stroke volume (SV), wall thickness (WT), heart rate (HR) as well as serum lactate concentration were measured after different levels of the graded exercise. Results were compared with those obtained in 11 male sport students (average age 26.4 [23-30] years), who had similarly trained for 5.6 +/- 1.3 h/week. RESULTS: The paraplegics had a significantly smaller LVV than the controls (771 +/- 84 ml vs 976 +/- 84 ml) and smaller SV (83 +/- 13 ml vs 104 +/- 11ml), with comparable WT. Paraplegics achieved significantly lower maximal exercise (145 +/- 23.7 vs 160 +/- 28.2) and maximal HR (177 +/- 12 vs 170 +/- 9) were not significantly different at the various exercise steps. CONCLUSION: Paraplegia decreases cardiac dimensions and function. Long-term physical exercise achieves results comparable with those of untrained but not of trained healthy controls. Physically active paraplegics showed physiological cardiovascular and metabolic reactions to exercise.

Adult↗

PubMed1996

The effects of calcium and other polyvalent cations on channel formation by Escherichia coli alpha-hemolysin in red blood cells and lipid bilayer membranes.

Channel formation by Escherichia coli alpha-hemolysin (HlyA) was studied in lipid bilayer membranes and in erythrocytes as a function of the concentration of divalent and trivalent cations. Hemolysin showed full channel-forming activity in artificial lipid bilayers, even in the presence of 5 mM EDTA and when the E. coli cells were grown in calcium-depleted media (< 1 microM Ca2+). The addition of divalent cations decreased the single-channel conductance by about 50% with half-saturation constants of 5 mM and less, while the mean lifetime of the HlyA channel was not affected. The addition of trivalent cations, such as Fe3+ or La3+, had a similar effect on the channel conductance, but the half-saturation constant was 1 microM or below. These effects may be caused by the binding of the cations to negatively charged groups at the channel mouth and have probably nothing to do with the possible binding of these cations to the repeat domain of the toxin, which is essential for target cell recognition. When cells were grown in calcium-depleted media, the supernatants showed absolutely no hemolytic activity. Addition of small amounts of Ca2+ to the supernatant led to toxin-mediated hemolysis. Its half-saturation constant was 120 microM. Of the other earth alkaline cations only strontium (Sr2+), which has an ion radius similar to Ca2+, led to full activation of HlyA with a K(m) of 1.5 mM. Ba2+ induced only weak hemolytic activity, while Mg2+ and several heavy metal cations had no effect. These results led to the conclusion that the target cell recognition sites formed by the repeat region of HlyA have defined sizes and bind only ions with defined radii.

Bacterial Proteins↗

PubMed1996

Isolation of mitochondrial porin of the fly Protophormia: porin modification by the pesticide CGA 140'408 studied in lipid bilayer membranes.

Mitochondrial porin from the fly Protophormia was solubilized with detergent from whole mitochondria and purified by chromatography across a hydroxyapatite (HPT) column. The purified protein had an apparent molecular mass of about 30 kDa on SDS-PAGE. Partial sequencing of the protein confirmed that it is porin. When reconstituted in planar lipid bilayer membranes, porin formed ion-permeable channels with single-channel conductances of 2.4 and 4.5 nS in 1 M KCl. At low voltage, Protophormia porin displayed the properties of a general diffusion pore and had a small selectivity for anions over cations. At transmembrane potentials starting with about 20-30 mV, the channel switched in closed state, which is still ion-permeable. Our results suggest that Protophormia porin possesses functional properties similar to those of other mitochondrial porins. Porin was also isolated and purified from mitochondria, which were treated with the carbodiimide CGA 140'408 It represents the active derivative of diafenthiuron a new acaricide and insecticide. This carbodiimide labels both a F0-component of the inner membrane ATPase and outer membrane porin in a similar way as N,N'-dicyclohexylcarbodiimide (DCCD). Reconstitution experiments with the CGA 140'408-modified porin showed no significant effect of the modification on the single-channel conductance, suggesting that CGA 140'408 binds outside the channel. The voltage-dependence of the CGA 140'408-modified porin was changed with respect to the unmodified form. The closed configuration of the pesticide-modified channel was reached at smaller transmembrane potentials, suggesting a shift of the open to the closed state of Protophormia porin by pesticide binding. A possible contribution of this effect to the pesticide action is discussed.

Amino Acid Sequence↗

PubMed1996

Involvement of Gs and Gi proteins in dual coupling of the luteinizing hormone receptor to adenylyl cyclase and phospholipase C.

Binding of lutropin/choriogonadotropin to its cognate receptor results in the activation of adenylyl cyclase and phospholipase C. The mechanism underlying the generation of this bifurcating signal is presently not known. To analyze the coupling mechanism of the LH receptor, activated G proteins were labeled with [alpha-32P]GTP azidoanilide and identified by selective immunoprecipitation. In membranes of bovine corpora lutea and of L cells stably expressing the murine LH receptor (LHR cells), human chorionic gonadotropin (hCG) led to incorporation of the label into alphas and alphai2. Stimulation of LHR cells or of L cells expressing the M5 muscarinic receptor (LM5 cells) with the respective agonist resulted in activation of phospholipase C in both cell lines. However, alphaq and alpha11 were only labeled upon stimulation of the M5 muscarinic receptor. Agonist-induced Ca2+ mobilization and inositol phosphate accumulation were partially sensitive to pertussis toxin, and the expression of the betagamma-stimulable phospholipase C isoforms beta2 and beta3 could be demonstrated in LHR cells. Overexpression of phospholipase C-beta2 led to increased hCG-stimulated inositol phosphate accumulation, and expression of a beta-ARK1 C-terminal polypeptide effectively suppressed hCG-mediated phosphatidylinositol hydrolysis. Thus, the LH receptor couples to both Gs and Gi, and betagamma-subunits released from either G protein contribute to the stimulation of phospholipase C-beta isoforms.

Adenylyl Cyclases↗

PubMed1996

Pleasure-attenuation of startle is disrupted by lesions of the nucleus accumbens.

The nucleus accumbens (NAC) and the amygdala have been implicated in processes by which reinforcers control instrumental behaviour. Reinforcement has both motivational and motor components, and it is necessary to differentiate between these two aspects. The acoustic startle response (ASR) is attenuated in the presence of a secondary reinforcer. In contrast to other paradigms used for investigating mechanisms of reward, the "pleasure-attenuated startle" (PAS) paradigm indicates the rewarding properties of a treatment by an attenuation rather than by reinforcement of a response, thus allowing determination of the motivational impact of a treatment independent from its motor stimulating effects. Here, we report that the ASR was attenuated in the presence of a positive conditioned stimulus in shamoperated animals and in rats with lesions of the amygdala, but not in animals bearing 6-hydroxydopamine lesions of the NAC. These findings suggest that the catecholaminergic innervation of the NAC is important for behavioural control by conditioned reward.

Acoustic Stimulation↗

PubMed1996

Modulation of Neisseria porin (PorB) by cytosolic ATP/GTP of target cells: parallels between pathogen accommodation and mitochondrial endosymbiosis.

PorB of the pathogenic Neisseria species belongs to the large family of pore-forming proteins (porins) produced by gram-negative bacteria. PorB is exceptional in that it is capable of translocating vectorially into membranes of infected target cells and functions in the infection process. Here we report on an unexpected similarity between Neisserial PorB and mitochondrial porins. Both porin classes interact with purine nucleoside triphosphates, which down-regulate pore size and cause a shift in voltage dependence and ion selectivity. Patch-clamp analyses indicate that PorB channel activity is tightly regulated in intact epithelial cells. In light of recent findings on the pivotal role of PorB in virulence and the prevention of phagosome lysosome fusion, these data provide important mechanistic clues on the intracellular pathogen accommodation reminiscent of mitochondrial endosymbiosis.

Adenosine Triphosphate↗

PubMed1996

Glutathione depletion potentiates MPTP and MPP+ toxicity in nigral dopaminergic neurones.

Glutathione levels are decreased in the substantia nigra of patients with Parkinson's disease. We studied whether glutathione depletion contributes to dopaminergic cell death using a specific inhibitor of glutathione biosynthesis, L-buthionine sulfoximine (BSO). We found no significant reduction of tyrosine hydroxylase-positive cells in the substantia nigra pars compacta (SNpc) when BSO was administered systemically to preweanling mice or locally to the SNpc of adult rats. However, the combination of BSO with MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) in preweanling mice and the combination of nigral injections of BSO with intrastriatal injections of MPP+ (1-methyl-4-phenylpyridinium), the active metabolite of MPTP in adult rats, potentiated the toxic effects of MPTP and MPP+ on nigral neurones. Our data show that glutathione depletion can result in cell death if the nigrostriatal system is metabolically compromised.

1-Methyl-4-phenylpyridinium↗

PubMed1996

Folding and membrane insertion of the trimeric beta-barrel protein OmpF.

We have studied folding and membrane insertion of the porin OmpF and compared it to OmpA. Both are beta-barrel membrane proteins from the outer membrane of Escherichia coli, OmpF forming trimers and OmpA monomers. Each of them can be unfolded in solubilized form in a water/urea mixture. Refolding is initiated by dilution into a dispersion of lipid vesicles or lipid/detergent vesicles, whereupon OmpF and OmpA refold and insert into the membranes. Folding and insertion of the monomers proceed in a similar way for the two proteins, but native OmpF appears more slowly and with a lower yield than native OmpA because of trimerization of OmpF. The dependence of the yield of refolding, membrane insertion, and trimerization on pH, lipid concentration, and the presence of detergent was investigated. Trimerization of OmpF is shown to take place at or in the membrane and a membrane-inserted dimer is detected as an intermediate of this process.

Bacterial Outer Membrane Proteins↗

PubMed1996

X-ray crystallographic and mass spectrometric structure determination and functional characterization of succinylated porin from Rhodobacter capsulatus: implications for ion selectivity and single-channel conductance.

The role of charges near the pore mouth has been discussed in theoretical work about ion channels. To introduce new negative charges in a channel protein, amino groups of porin from Rhodobacter capsulatus 37b4 were succinylated with succinic anhydride, and the precise extent and sites of succinylations and structures of the succinylporins determined by mass spectrometry and X-ray crystallography. Molecular weight and peptide mapping analyses using matrix-assisted laser desorption-ionization mass spectrometry identified selective succinylation of three lysine-epsilon-amino groups (Lys-46, Lys-298, Lys-300) and the N-terminal alpha-amino group. The structure of a tetra-succinylated porin (TS-porin) was determined to 2.4 A and was generally found unchanged in comparison to native porin to form a trimeric complex. All succinylated amino groups found in a mono/di-succinylated porin (MS-porin) and a TS-porin are localized at the inner channel surface and are solvent-accessible: Lys-46 is located at the channel constriction site, whereas Lys-298, Lys-300, and the N-terminus are all near the periplasmic entrance of the channel. The Lys-46 residue at the central constriction loop was modeled as succinyl-lysine from the electron density data and shown to bend toward the periplasmic pore mouth. The electrical properties of the MS-and TS-porins were determined by reconstitution into black lipid membranes, and showed a negative charge effect on ion transport and an increased cation selectivity through the porin channel. The properties of a typical general diffusion porin changed to those of a channel that contains point charges near the pore mouth. The single-channel conductance was no longer a linear function of the bulk aqueous salt concentration. The substantially higher cation selectivity of the succinylated porins compared with the native protein is consistent with the increase of negatively charged groups introduced. These results show tertiary structure-selective modification of charged residues as an efficient approach in the structure-function evaluation of ion channels, and X-ray crystallography and mass spectrometry as complementary analytical tools for defining precisely the chemically modified structures.

Amino Acid Sequence↗

PubMed1996

Localization of the angiotensin II receptor subtypes in the human atrium.

Angiotensin II has two major receptor subtypes, designated AT1 and AT2. Both have been detected in the heart of several species, but most of the known functions of angiotensin II seem to be mediated through the AT1 receptor. The major objective of this study was to specify the cell type on which the AT2 receptor is located in the atrium of human heart. Right atrial biopsies from patients with coronary artery disease were tested in membrane binding assays and found to contain high levels of angiotensin II receptor (820 +/- 175 fmol/mg), 82 +/- 2% of which was of the AT2 subtype. Cryostat sections of these biopsies were incubated with 125I-[Sar1,Ile8] angiotensin II in the presence of selective concentrations of the cold ligands losartan and CGP 42112A to detect the subtypes using microscopic autoradiography. High local densities of the AT2 receptor were observed. Comparison of the labelling patterns thus obtained with adjacent sections stained for vimentin, collagen, neurofilaments or acetylcholinesterase revealed that the high densities of AT2 receptor were always associated with fibrous tissue. However, the AT1 receptor was in general evenly distributed over the tissue at low concentrations. Higher local concentrations of this receptor subtype were observed on nervous tissue. The present finding of high densities of the AT2 receptor on fibroblasts at sites of fibrosis may have important clinical implications. Further studies to elucidate the function of this receptor subtype in the heart are therefore essential and the clinical consequences of the use of AT1 antagonists on post-infarction remodelling should be investigated.

Aged↗

PubMed1996

The role of sterols in the functional reconstitution of water-soluble mitochondrial porins from plants.

Water-soluble porins were prepared from native mitochondrial porins isolated from different plants (pea and corn). In the water-soluble form the porins have lost their channel-forming properties. The water-soluble porins were investigated for the influence of different sterols on their membrane activity and their channel-forming properties in lipid bilayer membranes. Our experiments demonstrated that the water-soluble porins regained channel forming activity when the protein was preincubated with different sterols in the presence of a detergent. The channels formed in lipid bilayer membranes after this procedure regain in many but not all cases the original properties of the native mitochondrial porins. Preincubation with other sterols led to a change in the single-channel conductance or to a complete loss of the voltage dependence. The sterols had also a strong influence on the channel-forming activity of the porins. Preincubation of water-soluble pea porin with the plant sterol beta-sitosterol resulted in a considerable higher channel-forming activity than with all the other sterols used for preincubation. The role of the sterols in the channel-forming complex is discussed.

Electric Conductivity↗

PubMed1996

Different time courses of GTP[gamma-S]-induced exocytosis and current oscillations in isolated mouse pancreatic acinar cells.

Exocytosis in isolated mouse pancreatic acinar cells was investigated using the dual-frequency method for measuring membrane capacitance and ionic conductances. Under control conditions, single exo- and endocytotic events could be resolved. The total cell capacitance slightly decreased to 98.7 +/- 0.9% of the initial cell capacitance within 10 min after establishing the whole-cell configuration. When guanosine 5'-O-(3-thiophosphate) (GTP[gamma-S] was added to the patch pipette, stepwise elevations in membrane capacitance occurred and the cell capacitance increased to 106.7 +/- 1.6% within 10 min. Exocytosis was also stimulated by GTP[gamma-S] when a Ca2+-free pipette solution supplemented with 1 to 10 mM ethylenebis(oxonitrilo) tetraacetate (EGTA) was used. Measurement of the DC current component in parallel with AC current analysis was used to isolate components of the Ca2+-dependent Cl- and monovalent cation conductances from the whole-cell conductance. These experiments demonstrate that in GTP[gamma-S]-stimulated pancreatic acinar cells: (1) activation of Cl- currents precedes that of cation currents, and (2) fusion of the zymogen granule membrane with the plasma membrane does not lead to incorporation of active Cl- or nonselective cation channels (>/= 10 pS).

Animals↗

PubMed1996

Leucokinin-like immunoreactive neurones in the central nervous system of the spider Cupiennius salei.

Leucokinin is a member of the myokinin peptide family. These myotropic peptides are widely distributed in arthropods. A specific antiserum immunoreactive to the neuroactive octapeptide leucokinin I (LKI) has been used to map neurones within the central nervous system of the central American wandering spider Cupiennius salei. The antiserum labels nine pairs of cell bodies and their axons. The somata are grouped near the joint of the optic lobes in the dorsal part of the supraoesophageal ganglion. The axons descend in a bundle, pass the oesophagus and divide to innervate the suboesophageal ganglion at three levels. In the dorsal-most layer, five small parallel fibres travel within the medio-central tract towards the opisthosomal neuromeres and give off small varicose projections into all leg neuromeres. In the middle layer, two neurones in the sensory-longitudinal tract 3 project into each leg neuromere. In the ventral layer, the two largest fibres (about 8 microm) run in the medio-ventral tract, each giving off a branch into all leg neuromeres. These first order arborizations have small second order arborizations in the ventral part of the leg neuromere and ascend to the five dorsal fibres in the medio-ventral tract where they form varicosities. The second order arborizations form extensive varicosities in the ventral part of the leg neuromere. These neurones may play a role in the intercellular communication between the sensory input and the motor output system, because they are represented in the dorsal sensory and the ventral motor neuropile. The ventral fibres resemble intersegmental interneurones and may function as modulators for leg motor neurones.

Animals↗

PubMed1996

Color vision in the manatee (Trichechus manatus).

Four manatees were trained to discriminate between a colored stimulus and a shade of gray in a two-fold simultaneous choice situation. The colors blue, green, red and blue-green were tested against shades of gray varying from low to high relative brightness. The animals distinguished both blue and green from a series of grays but failed to discriminate red and blue-green from certain steps of grays. The manatees could not discriminate between a UV-reflecting white target and an UV-absorbing white target. The results indicate that manatees possess color vision which is most likely dichromatic.

Animals↗

PubMed1996

Effect of physical exercise and vitamin C on absorption of ferric sodium citrate.

The effect of physical exercise and vitamin C on iron absorption after oral iron administration was investigated. Eight healthy male subjects without iron deficiency were studied after administration of 100 mg ferric sodium citrate complex, 100 mg ferric sodium citrate complex with 200 mg ascorbic acid, and without iron intake, both under resting conditions and after a 1-h bicycle ergometer test at moderate exercise. Serum concentrations for iron, transferrin, and ferritin were measured before and 30 min, and 1, 2, and 4 h after each administration. Under resting conditions administration of 100 mg ferric sodium citrate led to a significant increase in serum iron concentrations. When ferric sodium citrate was administered with vitamin C, iron values increased significantly further. Ingestion of iron together with physical exercise resulted in a higher serum iron concentration than under resting conditions. The maximum increase, reached after 4 h, was 48.2% with exercise and 8.3% without. In combination with exercise, the addition of 200 mg vitamin C did not further increase serum iron concentration. In conclusion, 1 h of moderate exercise enhanced the rate of iron absorption. Under resting conditions the combination of ferric sodium citrate with vitamin C led to significantly increased postabsorption serum iron concentrations compared with iron administration without vitamin C.

Adult↗

PubMed1996

G proteins of the Gq family couple the H2 histamine receptor to phospholipase C.

In several cell systems histamine has been shown to stimulate both adenylyl cyclase and phospholipase C through activation of a G protein-coupled H2 receptor. To analyze the bifurcating signal emanating from the activated H2 receptor and to identify the G proteins involved, H1 and H2 histamine receptors were functionally expressed in baculovirus-infected insect cells. Histamine challenge lead to concentration-dependent cAMP formation and Ca2+ mobilization in Sf9 cells infected with a virus encoding the H2 receptor, whereas H1 receptor stimulation only resulted in pronounced phospholipase C activation. To analyze the G protein coupling pattern of histamine receptors, activated G proteins were labeled with [alpha-32P]GTP azidoanilide and identified by selective immunoprecipitation. In insect cell membranes expressing H1 histamine receptors, histamine led to incorporation of the label into alpha q-like proteins, whereas activation of the H2 receptor resulted in labeling of alpha q- and alpha s-like G protein alpha-subunits. In COS cells transfected with H2 receptor complementary DNA, histamine caused concentration-dependent accumulation of cAMP and inositol phosphates; the latter effect was insensitive to pertussis toxin treatment. Histamine stimulation led to a pronounced increase in inositol phosphate production when complementary DNAs coding for alpha q, alpha 11, alpha 14, or alpha 15 G protein alpha-subunits were cotransfected. This increase was specific for Gq family members, as overexpression of alpha 12 or alpha s did not enhance histamine-stimulated phospholipase C activation. In membranes of guinea pig heart, addition of [alpha-32P]GTP azidoanilide resulted in labeling of alpha q and alpha 11 via the activated H1 and also via H2 receptors. These data demonstrate that dual signaling of the activated H2 histamine receptor is mediated by coupling of the receptor to Gs and Gq family members.

Adenylate Cyclase Toxin↗

PubMed1996

Mechanism and possible behavioural relevance of retinal movements in the ctenid spider Cupiennius salei

Like most spiders, the nocturnal hunting spider Cupiennius salei is able to move the retinae of its antero-median (AM) eyes. In the present study, the morphological and physiological properties of the eye muscles and the mechanism and behavioural relevance of retinal movements are investigated. The retinal movements are brought about by two forces: (i) contractions of the dorsal and ventral eye muscles, and (ii) the passive elastic restoring force of the eye tube and eye muscles (the presumed counteracting force). The dorsal eye muscle consists of 1518 striated fibres and is 600 µm long. The ventral eye muscle is longer (650 µm) and consists of 2022 striated fibres. The direction of the gaze of the retinae brought about by the eye muscles (active retinal movements) depends on the contraction states of the two eye muscles. The medially directed action of both eye muscles does not allow active movements of the eye tube in any lateral direction. Thus, the direction of gaze cannot actively be shifted medially. After active displacement of the retina, the elasticity of the eye tube and eye muscles passively moves the eye tube back to its resting position. There are two types of retinal movements. (i) Spontaneous microsaccades (duration 80 ms; excursion 3 °) are caused by the spontaneous contraction of only the dorsal eye muscle. They are ideally suited for preventing the adaptation of the sensory cells since their mean excursion (3 °) perfectly fits the inter-receptor angle (2.9 °) in the AM eye of Cupiennius salei. (ii) Induced movements (duration 100500 ms; excursions 415 °) are caused by the contraction of both eye muscles and occur only after mechanical stimulation. Induced movements were elicited by stimulating the mechanosensory organs (trichobothria and slit sense organs) of the spider's legs. A stimulus on one side of the spider induces movements of the ipsilateral retina only. We therefore suggest that induced retinal movements are saccades shifting the gaze of the spider laterally towards the site of mechanical stimulation. According to behavioural experiments, the ability of a spider to locate an immobile target is highly impaired after blinding its AM eyes. We suggest that the motility of the AM eyes is required to locate stationary objects.

Journal Article↗

PubMed1996

Ultrastructural aspects of the neuroendocrine complex in the stomach in patients with either pernicious anemia or the Zollinger-Ellison syndrome.

The neuroendocrine complex of the gastrointestinal tract is defined as the presence of neuroendocrine cells in the lamina propria and in direct contact with nerve fibres of Meissner's plexus. The entire complex is separated from the interstitium by a basement membrane. To date, only a few studies have been published on the neuroendocrine complex. In this prospective electron microscopic study, we investigated the neuroendocrine complex of the stomach in 21 patients with pernicious anemia, and in eight patients with the Zollinger-Ellison syndrome. For each patient, six step biopsies obtained from the stomach at endoscopy were investigated. 16 out of the 21 patients with pernicious anemia, and four of the eight patients with the Zollinger-Ellison syndrome were found to have neuroendocrine complexes in the gastric mucosa. In patients with pernicious anemia who had neuroendocrine complexes more neuroendocrine complex-positive biopsies were found, on average, per patient, and more and larger neuroendocrine complexes, on average, per biopsy, than was the case in patients with the Zollinger-Ellison syndrome. These results show that in the gastric mucosa of patients with pernicious anemia, more marked proliferation of neuroendocrine complexes occur than in patients with Zollinger-Ellison syndrome.

Adult↗