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At least 1,693 records · Page 94Linked to original sources
PubMed1991

A magnetization transfer preparation scheme for snapshot FLASH imaging.

A rapid method of generating images whose contrast is dependent on the exchange of magnetization between the free and restricted proton pools is presented. The contrast obtained is similar to that obtained from T2-weighted spin-echo images. The rapid nature of the sequence means that the RF power deposition problems encountered when using magnetization transfer in conjunction with conventional imaging sequences are avoided.

Electromagnetic Phenomena↗
PubMed1988

Flash labelling of S-phase cells in short-term organ culture of normal and pathological human endometrium using bromodeoxyuridine and tritiated thymidine.

Normal hyperplastic and malignant endometrial specimens were labelled in vitro with bromodeoxyuridine (BrdU). S-phase cells were stained after DNA denaturation, using a monoclonal antibody to BrdU and an indirect immunoperoxidase method. Various conditions for BrdU uptake, DNA denaturation, and staining were tested. BrdU labelling was compared with autoradiography using tritiated thymidine, with good correlation. Glandular labelling indices of proliferative endometrium were significantly higher than both secretory and hyperplastic endometrium but were similar to carcinoma. Stromal labelling showed the same trend but the differences were not statistically significant.

Autoradiography↗
PubMed1996

Interaction of polycyclic aromatic hydrocarbons with human cytochrome P450 1A1: a CO flash photolysis study.

The kinetics of CO binding to human cytochrome P450 1A1 was used to probe the interaction of polycyclic aromatic hydrocarbons (PAHs) with the membrane-bound P450 expressed in baculovirus-infected SF9 insect cells. Biexponential kinetics was observed, indicating that P450 1A1 is composed of at least two kinetically distinguishable species. To define the substrate specificity of the individual species, we evaluated the effect of a series of PAHs of varying sizes and shapes on the CO binding kinetics of P450 1A1. The overall rate of CO binding was increased in the presence of the tricyclic PAHs phenanthrene and anthracene and the tetracyclic PAHs pyrene and 1,2-benzanthracene, but was decreased by the pentacyclic PAHs benzo[a]pyrene and 1,2:3,4-dibenzanthracene. A kinetic difference method was applied to kinetically define the individual P450 1A1 species. Two species differing in their PAH specificities were identified: a slowly reacting species sensitive to the smaller PAHs, and a rapidly reacting species responsive to larger PAHs. Upon PAH binding, CO binding to these species was accelerated and decelerated, respectively. The results furthermore suggest that the two species are interconvertable. In addition to PAHs, the interactions of P450 1A1 with 7-ethoxy- and 7-pentoxyresorufin were likewise examined for their effect on the CO binding kinetics. These compounds interacted with and decreased the rate of the rapidly and slowly reacting P450 1A1 species, respectively. The markedly variable effects of these PAHs and resorufins on the CO binding kinetics indicate differential modes of interaction with the two target P450 1A1 species, resulting in differential modulation of their conformations. These results demonstrate that multiple P450 1A1 species with distinct conformations and substrate recognition profiles coexist in a biological membrane and are resolvable using a rapid kinetic technique.

Animals↗
PubMed1996

Flow-flash kinetics of O2 binding to cytochrome c oxidase at elevated [O2]: observations using high pressure stopped flow for gaseous reactants.

A high-pressure stopped-flow apparatus developed in our laboratories provides the capability to use dissolved gaseous reactants at elevated concentrations in solution (in equilibrium with gas pressures up to ca. 30 atm) for measurement of reaction kinetics. We have used this apparatus to follow the reaction of dioxygen with bovine cytochrome c oxidase following photolysis of the fully reduced CO ligated enzyme up to a dioxygen concentration of 16 mM. The observed rate dependence on [02] follows saturation kinetics and was fit to a limiting rate of 1.0 X 10(6) s(-1). This value is approximately the same as that for the thermal loss of CO to solution from the transient CuB bound state formed upon photolysis of the heme-CO complex. Implications for the mechanism of O2 binding and reduction by the heme-copper oxidases are discussed.

Animals↗
PubMed1993

Effects of ionic strength on force transients induced by flash photolysis of caged ATP in covalently crosslinked rabbit psoas muscle fibers.

Single fibers from glycerinated rabbit psoas muscle were treated with 1-ethyl-3[3-(dimethylamino) propyl] carbodiimide (EDC), after rigor was induced, to crosslink myosin heads to actin. The optimally pre-stretched (approximately 1.8%), partially crosslinked fibers produce a large force when MgATP is depleted, and this force is abolished when MgATP is reintroduced, even in high ionic strength solution of 0.5 M (Tawada et al. 1989). We investigated the rate of force decay in the crosslinked, force-producing fibers using pulse photolysis of caged ATP (Goldman et al. 1984). The decay of force was fast, the rate of which depending both on the ionic strength and on the amount of ATP released (0.2-2.2 mM) with the second-order rate constant of 0.5-1 x 10(5) M-1s-1 at the ionic strength of 0.5 M. At high ionic strength (1-2M) force decayed at lower rate. At low ionic strength (0.1-0.2 M), however, force decayed more rapidly, but force redeveloped subsequently, which is probably caused by uncrosslinked myosin heads.

Adenosine Triphosphate↗
PubMed1990

The effect of electrode position on flash visual evoked potentials in the newborn.

We examined how changes in electrode position affected the visual evoked potential in 74 high-risk newborns using a multiple electrode technique. The variation in the visual evoked potential across the occiput was documented. Visual evoked potentials that were visible at one occipital electrode position were absent at a different electrode position in 21 of 87 recordings (24%). Changes of greater than 20 msec between electrodes in latency of waves P1 or N2 occurred in 34% and 29% of recordings, respectively. The amplitude of response varied by a factor of 2.36 between mid occipital and lateral occipital electrodes. The results demonstrated that large changes in morphologic characteristics, latency, and amplitude in the visual evoked potential of the newborn result from small changes in the position of recording electrodes. These findings underscored the importance of electrode position and accurate electrode placement. Our observations also indicated that recordings from a single electrode are inadequate in providing an accurate representation of the neonatal visual evoked potential.

Evoked Potentials, Visual↗
PubMed1993

Flash photolysis studies of relaxation and cross-bridge detachment: higher sensitivity of tonic than phasic smooth muscle to MgADP.

The effects of MgADP and inorganic phosphate (Pi) on cross-bridge detachment were determined in tonic (rabbit femoral artery) and phasic (rabbit bladder and guinea pig portal vein) smooth muscles permeabilized with staphylococcal alpha-toxin. Relaxation from rigor was induced by photolysis of ATP (1.2-1.5 mM) from caged ATP. The initial one second of relaxation from rigor was resolved into two exponential components: a rapid component with normalized amplitudes, Af, of 8, 15 and 26% and rate constants, kf (in s-1) of 26, 36 and 30 in rabbit femoral artery, guinea pig portal vein, and rabbit bladder; the respective rate constants of the second, slower component, ks, were 0.07, 0.2 and 0.1. Removal of residual endogenous ADP with apyrase treatment increased the amplitude Af and accelerated ks; addition of MgADP reduced Af. The combination of these effects (increases in Af and ks) decreased the t1/2 of relaxation from control values by factors of 2.6 (femoral artery), 6.7 (portal vein) and 10 (bladder). Pi (30 mM) further increased the amplitudes Af. The affinity of MgADP for myosin cross-bridges, estimated as the reduction of the relative amplitude of the rapid component, Af, was significantly higher in tonic than in phasic smooth muscle: the KD of MgADP was 1.1 +/- 0.3 microM in rabbit femoral artery and 4.9 +/- 1.0 microM in rabbit bladder. The higher affinity of tonic smooth muscle myosin for MgADP correlated with its relatively high LC17b isoform content (58 +/- 4.2%) in contrast to the lower affinity of the phasic, bladder detrusor smooth muscle that contained only the LC17a isoform.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Diphosphate↗
PubMed1977

Nystagmus induced by intermittent photic stimulation (flash induced nystagmus (FIN).

In man, as has been shown previously in rabbits and monkeys, a nystagmus can be elicited by monocular intermittent photic stimulation. The direction of nystagmus (FIN) is always towards the stimulated eye. This nystagmus strongly resembles latent nystagmus. Here the fast phase is always directed towards the 'non-occluded' eye. The FIN may, therefore, be used as a model for the study of mechanisms underlying these pathological conditions. For further elucidation of FIN, studies were made in rabbits.

Animals↗
PubMed1991

A model for the variability of maintained discharges and responses to flashes of light.

Previous studies of the variability of firing of retinal ganglion cells have led to apparently contradictory conclusions. To a first approximation, maintained discharges derive their variability from a noise source that is linearly added to the signal setting the mean firing rate. On the other hand, the variability of responses to abrupt changes in lighting seems to result from a nonlinear interaction between signal and noise. In both the cat and the goldfish retinae, the variance of rate is a fractional power function of the mean response amplitude (impulses/s). The exponent of that power function depends on the duration of the period in which the response is sampled after each transition in luminance; longer durations have a larger exponent. These results are difficult to explain with any simple model. The variability of the maintained discharges also deviates from the predictions of simple additivity. We propose a model for the variability of responses to abrupt changes in lighting that incorporates variability of the form observed for maintained discharges. The parameters of our model that provide the best fits to the variability of responses also provide a reasonable fit to the variability of maintained discharges. Thus, a single explanation can account for the variability of maintained discharges and responses of ganglion cells.

Animals↗
PubMed1987

10-Hz flash visual evoked potentials predict post-cataract extraction visual acuity.

Cataract patients suspected of having disease which might interfere with good postoperative visual function were referred for evaluation. Monocular steady-state luminance visual evoked potentials (VEPs) were elicited with closed eyes at a stimulus rate of 10 flashes/sec. VEPs were rated as either normal or abnormal. Patients with normal VEPs were predicted to have an acuity of 6/15 (20/50) or better. Patients with abnormal VEPs were predicted to have acuities of 6/18 (20/60) or worse. Postoperative acuities were determined for all patients who underwent surgery and who had no intraoperative or early postoperative complications. The association of preoperative VEPs and observed postoperative acuities were quantitatively compared by a 2 x 2 contingency table for the 59 eyes which met these criteria. The chi-square was significant (p less than 0.001). The overall accuracy of prediction was 76%. Accuracy was 80% for patients with a preoperative acuity of 6/60 (20/200) or better and 75% for those whose postoperative acuity was 6/120 (20/400) or worse. This difference was not statistically significant.

Cataract Extraction↗