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W Sigurdson

Publications and source records attributed to W Sigurdson.

8 recordsLinked to original sources
PubMed2005

Synergy between Tannerella forsythia and Fusobacterium nucleatum in biofilm formation.

During dental plaque formation, the interaction of different organisms is important in the development of complex communities. Fusobacterium nucleatum is considered a 'bridge-organism' that facilitates colonization of other bacteria by coaggregation-mediated mechanisms and possibly by making the environment conducive for oxygen intolerant anaerobes. These studies were carried out to determine whether coaggregation between F. nucleatum and Tannerella forsythia is important in the formation of mixed species biofilms. Further, the role of BspA protein, a surface adhesin of T. forsythia, in coaggregation and biofilm formation was investigated. The results showed the development of synergistic mixed biofilms of F. nucleatum and T. forsythia when these bacteria were cocultured. The BspA protein was not involved in biofilm formation. Though BspA plays a role in coaggregation with F. nucleatum, presumably other adhesins are also involved. The synergistic biofilm formation between the two species was dependent on cell-cell contact and soluble components of the bacteria were not required. This study demonstrates that there is a positive synergy between F. nucleatum and T. forsythia in the development of mixed biofilms and that the cell-cell interaction is essential for this phenomenon.

Adhesins, Bacterial↗
PubMed2000

Mechanically induced calcium movements in astrocytes, bovine aortic endothelial cells and C6 glioma cells.

Forces applied to resting primary astrocytes, bovine aortic endothelial cells and C6 glioma cells with collagen-coated magnetite particles produce a fast transient change of intracellular Ca(2+). It peaks in the micromolar range as measured by Fura-2. This mechanical response adapts within seconds so that repeated stimulation causes smaller responses requiring >10 min for recovery. When cytoplasmic Ca(2+) is high after treating with ATP, cyclopiazonic acid and thapsigargin, stimulation causes a transient decrease in Ca(2+). In these three cell types, no influx of ions is required for Ca(2+) elevation showing the response is not caused by activation of plasmalemmal mechanosensitive channels. Approximately half the cells tested showed similar behavior, while the other half, such as fibroblasts, required extracellular Ca(2+). The Ca(2+) response is not temperature sensitive suggesting the possible involvement of intracellular mechanosensitive channels. We tested a number of second messenger reagents and were only able to block the response in BAECs, but not C6 glioma cells, with Xestospongin C, a blocker of IP(3)-activated channels. Despite the lack of a causal involvement of plasmalemmal mechanosensitive channels, mechanical stimulation immediately activates a persistent Mn(2+) influx pathway. This Mn(2+) pathway may be mechanosensitive channels, Ca(2+)-activated cation channels or depletion-activated Ca(2+) channels.

Adenosine Triphosphate↗
PubMed2000

Visual loss after spine surgery: a survey.

OBJECTIVE: To survey a large number of neurosurgical spine surgeons for data regarding the presence of risk factors in patients experiencing visual loss after spine surgery. METHODS: A survey was sent to current members (as of 1997) of the American Association of Neurological Surgeons/Congress of Neurological Surgeons, Section on Disorders of the Spine and Peripheral Nerves, with questions focusing on intraoperative factors that may predispose patients to perioperative visual loss. RESULTS: Two hundred ninety surveys were returned, and 24 patients with visual loss after spine surgery were reported by 22 surgeons. Although many of these patients had probable causative factors for visual loss after surgery (e.g., hypotension, low hematocrit level, coexisting disease), some did not (n = 8). CONCLUSION: These results suggest the necessity of a high index of suspicion for evolving perioperative visual loss even in the absence of risk factors.

Adolescent↗
PubMed1997

Storing analog data in a video record.

We have designed a simple device that will encode, in machine readable form, multiple analog data in a video record. The analog data is visible to the user within the video frame permitting visual correlation of these signals with activity observed in the image. By superimposition of both analog and video data sets, the two are tightly synchronized and remain so in all copies of the data. The analog data can be separated from the image following digitization by a frame grabber. The bandwidth for each of the five analog channels is approximately 5 kHz. The device, which is essentially an eight channel video multiplexor, includes a video channel, a field counter, an amplitude calibration signal and five analog data channels. The amplitude calibrator allows corrections for gain errors that are particularly prevalent when data is stored on video tape.

Calibration↗
PubMed1996

Voltage dependence of mouse acetylcholine receptor gating: different charge movements in di-, mono- and unliganded receptors.

1. The voltage dependence of binding and gating in wild-type and mutant recombinant mouse nicotinic acetylcholine receptors (AChRs) was examined at the single-channel level. 2. The closing rate constant of diliganded receptors decreased e-fold with approximately 66 mV hyperpolarization in both wild-type (adult and embryonic) and mutant receptors. The opening rate constant of a mutant receptor (alpha Y93F) was not voltage dependent. 3. The voltage dependence of closing in monoliganded receptors was examined in several receptors having a mutation in the binding site (alpha G153S) or pore region (alpha L251C and epsilon T264P). The closing rate constant of these monoliganded receptors decreased e-fold with approximately 124 mV hyperpolarization. 4. The voltage dependence of closing and opening in unliganded receptors was examined in two receptors having a mutation in the pore region (alpha L251C and epsilon T264P). Neither the closing nor the opening rate constants of unliganded receptors were voltage dependent. 5. If z if the amount of charge that moves during channel closure and delta is the distance (as a fraction of the electric field) that the charge moves, we conclude that z delta = 0.4 in diliganded receptors, 0.2 in monoliganded receptors, and 0.0 in unliganded receptors. It is likely that charges on the protein, rather than the agonist molecule, move z delta = 0.2 after each ACh molecule has bound. 6. The results suggest that unliganded openings arise from a local, concerted change in the structure of the pore (channel opening) that does not involve the net movement of charged residues. We speculate that as a consequence of agonist binding, charged moieties in the protein change their disposition so that they move with respect to the electric field when the channel gates. The results are consistent with the idea that there is semi-independent movement of distinct domains during AChR gating.

Acetylcholine↗
PubMed1992

Calcium imaging of mechanically induced fluxes in tissue-cultured chick heart: role of stretch-activated ion channels.

Heart rate and contractility are sensitive to stretch. To better understand the origin of these effects, we have studied the effect of mechanical stimuli on a model system of tissue-cultured heart cells. Gently prodding cells with a pipette produced a Ca2+ influx that often led to waves of calcium-induced calcium release (CICR) spreading from the site of stimulation. Ca2+ release could also be produced by pulling on neighboring cells. The response was blocked by removing extracellular Ca2+ or by adding 20 microM Gd3+ to normal saline. The mechanical sensitivity probably arose from stretch-activated ion channels (SACs) based on several lines of evidence. Chick heart cells contain nonselective cation SACs that pass Ca2+ as well as Na+ and K+. Both the SACs and the fluorescence response are blocked by 20 microM Gd3+. Removal of Ca2+ from the extracellular medium blocked the fluorescent response. Cultures without SACs (grown in the absence of embryo extract) had no mechanically induced fluxes. These data contradict the recent claim that SAC activity is a patch-clamp artifact (C.E. Morris and R. Horn, Science Wash. DC 256: 1246-1249, 1991). The SACs had a density of approximately 1/micron 2 and were expected to pass less than 20 fA of Ca2+ current under physiological conditions. The change in intracellular concentration of Ca2+ ([Ca2+]i) resulting from activation of SACs may be too small to induce CICR unless the channels pass current into a restricted space (N. LeBlanc and J.R. Hume, Science Wash. DC 248: 372, 1990).(ABSTRACT TRUNCATED AT 250 WORDS)

Aniline Compounds↗