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Biomedical subjects

S Richter

Publications and source records attributed to S Richter.

At least 109 records · Page 6Linked to original sources
PubMed1997

The monovalent cation "leak" transport in human erythrocytes: an electroneutral exchange process.

The mechanism of the "ground permeability" of the human erythrocyte membrane for K+ and Na+ was investigated with respect to a possible involvement of a previously unidentified specific transport pathway, because earlier studies showed that it cannot be explained on the basis of simple electrodiffusion. In particular, we analyzed and described the increase in the (ouabain+bumetanide+EGTA)-insensitive unidirectional K+ and Na+ influxes as well as effluxes (defined as "leak" fluxes) observed in erythrocytes suspended in low-ionic-strength media. Using a carrier-type model and taking into account the influence of the ionic strength on the outer surface potential according to the Gouy-Chapman theory (i.e., the ion concentration near the membrane surface), we are able to describe the altered "leak" fluxes as an electroneutral process. In addition, we can show indirectly that this electroneutral flux is due to an exchange of monovalent cations with protons. This pathway is different from the amiloride-sensitive Na+/H+ exchanger present in the human red blood cell membrane and can be characterized as a K+(Na+)/H+ exchanger.

Binding Sites↗
PubMed1997

Liver ischemia/reperfusion induces an increase of microvascular leukocyte flux, but not heterogeneity of leukocyte trafficking.

Leukocytic response plays a major role in the manifestation of hepatic ischemia/reperfusion (I/R) injury. To clarify whether post-ischemic hepatic leukocyte accumulation is based on increased leukocyte flux to the hepatic tissue due to systemic inflammation or chemoattractant activities or whether it represents solely a local tissue response without changing overall leukocyte flux and trafficking characteristics through the microvasculature, we studied acinar and sinusoidal leukocyte flux and distribution in rat livers in vivo both under normal (sham, n = 8) and post-ischemic (60' ischemia/75' reperfusion) conditions (I/R, n = 8), using fluorescence epi-illumination microscopy (rhodamine-6G). Hepatic ischemia/reperfusion significantly (p < 0.05) increased acinar leukocyte flux (58.4 +/- 20.9 cells/min vs 36.4 +/- 12.8 cells/min in sham controls); however, it did not exhibit increased heterogeneity of acinar leukocyte distribution, as indicated by the unchanged coefficient of variance (CV) of 0.36 +/- 0.16 (sham controls: 0.31 +/- 0.14). In parallel, analysis of individual sinusoidal leukocyte flux demonstrated significantly (p < 0.05) higher values (8.9 +/- 3.7 cells/min) after ischemia/reperfusion when compared with sham controls (5.7 +/- 1.9 cells/min), which, however, was not associated with increased heterogeneity of sinusoidal leukocyte trafficking (CV: 0.85 +/- 0.15 vs 0.85 +/- 0.16 in sham controls) and manifestation of preferential pathways. Analysis of blood cell count did not demonstrate an overall increase of total blood leukocyte count; however, an increased (p < 0.01) fraction of polymorphonuclear leukocytes (65.2 +/- 11.2%) and stab cells (9.5 +/- 7.9%) during post-ischemic reperfusion when compared with sham controls (8.8 +/- 3.5% and 0.2 +/- 0.4%) was demonstrated. Thus, the increase of hepatic leukocyte flux after ischemia/reperfusion may be the result of both the manifestation of a systemic inflammatory response and the increase of local chemoattractant activities, such as the production and release of the cytokine-induced neutrophil chemoattractant of the IL-8 family.

Animals↗
PubMed1997

The ggtA gene encodes a subunit of the transport system for the osmoprotective compound glucosylglycerol in Synechocystis sp. strain PCC 6803.

The ggtA gene was sequenced during the analysis of a mutant of Synechocystis sp. strain PCC 6803 with impaired salt tolerance. It showed striking sequence similarities to ATP-binding proteins of binding-protein-dependent transport systems (ABC transporters). Mutants of ggtA and three neighboring reading frames were constructed by inserting an aphII gene cassette and were physiologically and genetically characterized. The ggtA insertion mutant lost its glucosylglycerol (GG) uptake ability, but its salt tolerance did not change. Therefore, it was concluded that active transport of the osmoprotective compound GG in Synechocystis is mediated by an ABC transporter. The genes for the GG-specific ABC transporter are not organized in an operon as usually found for comparable transporters, since the other insertion mutants showed normal GG transport activity. After cultivation of the ggtA mutant at high salt concentrations, significant amounts of GG were found in the cultivation medium, indicating that GG transport is mainly necessary for recovery of GG leaked through the cytoplasmic membrane. The Northern blot technique revealed increased transcription of the ggtA gene in cells adapted to higher salt concentrations, whereas in cells from basal medium, its transcription was weak.

ATP-Binding Cassette Transporters↗
PubMed1997

Leukocyte migration in acute colonic inflammatory bowel disease: comparison of histological assessment and Tc-99m-HMPAO labeled leukocyte scan.

UNLABELLED: Noninvasive leukocyte scintigraphy for assessment of localization, extent, and degree of active inflammation in acute colonic inflammatory bowel disease have been shown to correlate well with endoscopy. This study compared findings of mucosal leukocyte migration assessed histologically with those of technetium 99m hexamethylpropylene-amineoxime-labeled leukocyte scintigraphy. PATIENTS AND METHODS: Twenty-one patients hospitalized because of a first attack or a relapse of known inflammatory bowel disease were investigated using leukocyte scintigraphy followed by total colonoscopy with multiple biopsies within 24 h. Histological interpretation focused on the degree of segmental mucosal leukocyte infiltration. RESULTS: Fourteen patients with ulcerative colitis (UC) and seven with colonic Crohn's disease (CD) were included. With the use of histology as the reference method, maximal proximal disease extent was correctly assessed by the leukocyte scan in 11 patients (8 with UC, 3 with CD), although the rectal involvement was not visualized in 5. In seven patients, the extent assessments almost matched (+/- one segment), and in the remaining three patients (two UC, one CD) the scan grossly misinterpreted active histological inflammation (> or = +/- two segments). In patients with UC, the sensitivity, specificity, and diagnostic accuracy concerning the extent of inflammation were 0.84, 0.79, and 0.83, respectively. In patients with CD, the sensitivity was 0.79, and the diagnostic accuracy was 0.78. The relative leukocyte scan activity score was less concordant with the degree of mucosal leukocyte infiltration but still significantly correlated (r = 0.616, p < 0.0001 in UC patients and r = 0.441, p < 0.003 in CD patients). CONCLUSION: Images created by the technetium 99m hexamethylpropylene-amineoxime-labeled leukocyte scan in acute colonic inflammatory bowel disease correlate to mucosal leukocyte migration in terms of proximal disease extent and, to a lesser degree, also to the intensity of mucosal inflammatory infiltration.

Acute Disease↗
PubMed1996

Instant technetium 99m hexamethyl propylenamine oxime-labeled leukocyte scan compared with colonoscopy in early assessment of disease extent and activity in acute colitis.

AIM: This study was undertaken to evaluate technetium 99m (Tc 99m) hexamethyl propylenamine oxime (HMPAO)-labeled leukocyte scintigraphy for assessment of disease extent and activity in acute colitis. PATIENTS AND METHODS: Twenty-seven patients, hospitalized because of acute watery and/or bloody diarrhea, were investigated using both total colonoscopy and Tc 99m HMPAO-labeled leukocyte scintigraphy within 48 hours after admittance. RESULTS: Final diagnoses were ulcerative colitis in 14 patients, Crohn's disease in 7 patients, and infectious colitis in 6 patients. Using colonoscopy as the reference method, the maximum extent of colitis was correctly assessed by the leukocyte scan in 18 patients (67 percent), although rectal engagement was not visualized in 5 (19 percent). In six additional patients, there was almost complete agreement between the two methods. One other patient, with leftsided ulcerative colitis, was erroneously assessed as having total extent. Two other patients (one with Crohn's colitis and one with infectious colitis) had different segments incorrectly assessed. Sensitivity, specificity, and diagnostic accuracy of scintigraphy in detecting active inflammatory segments were 0.85, 0.83, and 0.85, respectively. Intensity of inflammatory activity assessed by the leukocyte scan correlated significantly with colonoscopic assessment (r = 0.719; P < 0.0001). CONCLUSION: Information regarding extent, localization, and disease activity in patients with acute colitis of inflammatory or infectious origin may be satisfactorily obtained using Tc 99m HMPAO-labeled leukocyte scanning. The noninvasive nature of the method makes it an attractive early alternative to other investigational procedures such as total colonoscopy or barium examination, particularly in cases with an established diagnosis of inflammatory bowel disease.

Acute Disease↗
PubMed1996

Characterization of a glucosylglycerol-phosphate-accumulating, salt-sensitive mutant of the cyanobacterium Synechocystis sp. strain PCC 6803.

Salt-sensitive mutants of Synechocystis were obtained by random cartridge mutagenesis, and one mutant (mutant 4) was characterized in detail. The salt tolerance of mutant 4 was reduced to about 20% of that of the wild-type. This was caused by a defect in the biosynthetic pathway of the osmoprotective compound glucosylglycerol (GG). Salt-treated cells of mutant 4 accumulated the intermediate glucosylglycerol-phosphate (GG-P). Only low levels of phosphate-free GG were detected. The phosphorylated form of GG was not osmoprotective and seemed to be toxic. In vitro enzyme assays revealed that GG-P-phosphatase activity was completely absent in mutant 4, while GG-P-synthase remained unchanged. The integration site of the aphII cartridge in mutant 4 and the corresponding wild-type region was cloned and sequenced. Mutant 4 was complemented to salt resistance after transformation by the cloned wild-type region. The integration of the cartridge led to a deletion of about 1.1 kb of the chromosomal DNA. This affected two of the identified putative protein coding regions, orfII and stpA. The ORFII protein shows a high degree of similarity to the receiver domain of response regulator proteins. Related sequences were not found for StpA. We assume that in mutant 4, regulatory genes necessary for the process of salt adaptation in Synechocystis are impaired.

Amino Acid Sequence↗
PubMed1996

A comprehensive set of DnaA-box mutations in the replication origin, oriC, of Escherichia coli.

We probed the complex between the replication origin, oriC, and the initiator protein DnaA using different types of mutations in the five binding sites for DnaA, DnaA boxes R1-R4 and M: (i) point mutations in individual DnaA boxes and combinations of them; (ii) replacement of the DnaA boxes by a scrambled 9 bp non-box motif; (iii) positional exchange; and (iv) inversion of the DnaA boxes. For each of the five DnaA boxes we found at least one type of mutation that resulted in a phenotype. This demonstrates that all DnaA boxes in oriC have a function in the initiation process. Most mutants with point mutations retained some origin activity, and the in vitro DnaA-binding capacity of these origins correlated well with their replication proficiency. Inversion or scrambling of DnaA boxes R1 or M inactivated oriC-dependent replication of joint replicons or minichromosomes under all conditions, demonstrating the importance of these sites. In contrast, mutants with inverted or scrambled DnaA boxes R2 or R4 could not replicate in wild-type hosts but gave transformants in host strains with deleted or compromised chromosomal oriC at elevated DnaA concentrations. We conclude that these origins require more DnaA per origin for initiation than does wild-type oriC. Mutants in DnaA box R3 behaved essentially like wild-type oriC, except for those in which the low-affinity box R3 was replaced by the high-affinity box R1. Apparently, initiation is possible without DnaA binding to box R3, but high-affinity DnaA binding to DnaA box R3 upsets the regulation. Taken together, these results demonstrate that there are finely tuned DnaA binding requirements for each of the individual DnaA boxes for optimal build-up of the initiation complex and replication initiation in vivo.

Bacterial Proteins↗
PubMed1996

Leukocyte stasis in hepatic sinusoids.

There is ongoing debate on the significance of capillary leukostasis for the manifestation of ischemia-reperfusion (I/R)-induced capillary "no-reflow". Using intravital fluorescence microscopy, we studied leukocyte trafficking through the hepatic microvasculature and the relevance of sinusoidal leukostasis for nutritive perfusion failure in rats after hepatic I/R (n = 8). Sham-operated animals (n = 8) served as controls. Hepatic reperfusion was characterized by perfusion failure of individual sinusoids and a significant increase of sinusoidal leukostasis. However, in both nonischemic and postischemic livers, the major fraction of sinusoids presenting with stagnant leukocytes were found perfused (97 +/- 1 and 73 +/- 5%, respectively), whereas only 3 +/- 1 and 27 +/- 5% failed to conduct flow. Analysis of leukocyte trafficking in sinusoids with leukostasis revealed a marked reduction of leukocyte velocity and leukocyte flux in nonischemic and postischemic livers compared with sinusoids without leukostasis. Thus stagnant leukocytes retard cellular passage through hepatic sinusoids, probably due to an increase of flow resistance. However, the fact that during postischemic reperfusion > 70% of the sinusoids accommodating stagnant leukocytes are still perfused indicates that sinusoidal leukostasis per se does not necessarily determine perfusion failure ("no-reflow") after I/R of the liver.

Animals↗
PubMed1996

Zebrafish mutations affecting retinotectal axon pathfinding.

We have isolated mutants in the zebrafish Danio rerio that have defects in axonal connectivity between the retina and tectum. 5-day-old fish larvae were screened by labeling retinal ganglion cells with DiI and DiO and observing their axonal projections to and on the tectum. 82 mutations, representing 13 complementation groups and 6 single allele loci, were found that have defects in retinal ganglion cell axon pathfinding to the tectum. These pathfinding genes fall into five classes, based on the location of pathfinding errors between eye and tectum. In Class I mutant larvae (belladonna, detour, you-too, iguana, umleitung, blowout) axons grow directly to the ipsilateral tectal lobe after leaving the eye. Class II mutant larvae (chameleon, bashful) have ipsilaterally projecting axons and, in addition, pathfinding mistakes are seen within the eye. In Class III mutant larvae (esrom, tilsit, tofu) fewer axons than normal cross the midline, but some axons do reach the contralateral tectal lobe. Class IV mutant larvae (boxer, dackel, pinscher) have defects in axon sorting after the midline and retinal axons occasionally make further pathfinding errors upon reaching the contralateral tectal lobe. Finally, Class V mutant larvae (bashful, grumpy, sleepy, cyclops, astray) have anterior-posterior axon trajectory defects at or after the midline. The analysis of these mutants supports several conclusions about the mechanisms of retinal axon pathfinding from eye to tectum. A series of sequential cues seems to guide retinal axons to the contralateral tectal lobe. Pre-existing axon tracts seem not to be necessary to guide axons across the midline. The midline itself seems to play a central role in guiding retinal axons. Axons in nearby regions of the brain seem to use different cues to cross the ventral midline. Mutant effects are not all-or-none, as misrouted axons may reach their target, and if they do, they project normally on the tectum. The retinotectal pathfinding mutants reveal important choice points encountered by neuronal growth cones as they navigate between eye and tectum.

Animals↗
PubMed1996

Mutations disrupting the ordering and topographic mapping of axons in the retinotectal projection of the zebrafish, Danio rerio.

Retinal ganglion cells connect to their target organ, the rectum, in a highly ordered fashion. We performed a large-scale screen for mutations affecting the retinotectal projection of the zebrafish, which resulted in the identification of 114 mutations. 44 of these mutations disturb either the order of RGC axons in the optic nerve and tract, the establishment of a topographic map on the tectum, or the formation of proper termination fields. Mutations in three genes, boxer, dackel and pinscher, disrupt the sorting of axons in the optic tract but do not affect mapping on the tectum. In these mutants, axons from the dorsal retina grow along both the ventral and the dorsal branch of the optic tract. Mutations in two genes, nevermind and who-cares, affect the dorsoventral patterning of the projection. In embryos homozygous for either of these mutations, axons from dorsal retinal ganglion cells terminate ventrally and dorsally in the tectum. In nevermind, the retinotopic order of axons along the optic nerve and tract is changed in a characteristic way as well, while it appears to be unaffected in who-cares. Two mutations in two complementation groups, gnarled and macho, affect the anteroposterior patterning of the projection. In these mutants, nasodorsal axons branch and terminate too soon in the anterior tectum. In 27 mutants belonging to six complementation groups, retinal axons do not form normal termination fields. Some implications for models concerning the formation of topographic projections are discussed.

Animals↗
PubMed1996

Correction of congenital or acquired penile curvature through a simple corporoplication technique.

Sexual dysfunction resulting from penile deformity is amenable to surgical correction. Thirty-five cases of penile deformity either 29 congenital or six secondary to Peyronie's disease were treated by simple plication of the tunica albuginea with non-absorbable sutures through a small skin incision made on the convex side of the curved penis. Postoperative complications such as impaired erection or loss of sensitivity of the glans were not reported. After an average follow-up of 36 months (range 12-60 months) all patients have straight erections and retain normal erectile function.

Adolescent↗
PubMed1996

Cancer screening in primary care: strategies for your office. A program of the Connecticut Division of the American Cancer Society.

Primary-care physicians' compliance with cancer screening guidelines has been in general unsatisfactory. Mailings have not had the desired effect upon these busy physicians who are preoccupied with many other issues. The Ohio Division of the American Cancer Society developed a program of in-office cancer screening education of primary-care physicians which resulted in a significant improvement in compliance to cancer screening guidelines. The Connecticut Division of the American Cancer Society has pursued this concept with their own program of visits targeted at physicians and their office staffs. A description of this program, which is still in its initial phases, is presented. The impact will be evaluated in due time, however additional volunteers to conduct these visits are needed.

Connecticut↗
PubMed1995

Application of the API YeastIdent system in determining the enzymatic profiles of Nocardia asteroides isolates.

Glucose represses production of ammonium in many clinical isolates of Nocardia asteroides growing on bromcresolpurple casein glucose agar. Strains exhibiting this property are designated as group A, while group B represents isolates showing a high degree of proteolytic activity and a resulting rapid increase in pH. Twenty isolates of N. asteroides were characterized as group A or B. Enzymatic profiles obtained using the API YeastIdent system showed significant enzymatic variation between 12 group B and 8 group A isolates. Proteolytic enzymes which most varied in activity between groups were glycine aminopeptidase, histidine aminopeptidase and leucyl glycine aminopeptidase. As some of the N. asteroides isolates were isolated from asymptomatic patients, it is of interest to consider the possibility of one group being of low virulence while the other is more strongly associated with infection.

Bacterial Typing Techniques↗
PubMed1995

Beta-endorphin, but not substance-P, is increased by acute stress in humans.

The role of neuropeptides in the psychoneuroendocrinological stress response is largely unknown. In this study the effect of acute psychological stress on beta-endorphin and substance-P plasma concentrations was investigated and further the effect of different anxiety levels or control attributions on beta-endorphin or substance-P levels were determined. Blood samples were obtained from 47 inexperienced tandem-parachutists 2 h before, immediately after, and 1 h after a parachute jump and plasma concentrations of beta-endorphin and substance-P were analysed. Anxiety levels and control attributions were assessed by psychometric scales. Whereas substance-P concentrations seemed to be unaffected by the jump stress, there was a transient but significant increase in beta-endorphin levels immediately after jumping. However, subjects higher in state-anxiety at the point of jumping (exit) displayed higher substance-P values at all three time points compared to the "low-anxiety" jumpers. In addition, stress-induced beta-endorphin secretion was dependent on subjective control attributions.

Adult↗
PubMed1995

Genetic structure of the dnaA region of the cyanobacterium Synechocystis sp. strain PCC6803.

We have cloned and sequenced the dnaA region of Synechocystis sp. strain PCC6803, a bacterium with a light-dependent cell cycle. The dnaA gene product, DnaA, is the central factor for replication initiation in bacteria. The deduced amino acid sequence of the protein encoded by the cyanobacterial dnaA gene is 45% identical to DnaA of Bacillus subtilis and fits very well into the homology pattern of the known eubacterial DnaA proteins. The genetic environment of the Synechocystis sp. strain PCC6803 dnaA gene is completely different from the one in other eubacteria. An open reading frame of unknown function, orf134, was detected upstream of dnaA. The purT gene homolog encoding the glycinamide ribonucleotide transformylase T starts about 200 bp away from this open reading frame in the opposite direction. Downstream of the dnaA gene we detected the start of the psbDC operon, which codes for the photosystem II reaction center proteins D2 and CP43 that are involved in the positioning of chlorophyll a.

Acyltransferases↗