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At least 55 records · Page 3Linked to original sources
PubMed2003

Effects of in vivo freezing and mannitol in intestinal ischaemia-reperfusion injury.

PURPOSE: The main purpose of this study was to investigate whether in vivo freezing and mannitol administration can protect the small intestine against ischaemia-reperfusion (I-R) injury. METHODS: Fifty male Sprague-Dawley rats (200-225 g) were divided into 5 groups each containing 10 rats; group SO, sham operation group; group I, mesenteric ischaemia group; group R, ischaemia-reperfusion (I-R); group FR, I-R plus in vivo freezing; group MR, I-R plus mannitol treatment. Intestinal ischaemia for 30 min and reperfusion for 60 min were applied. Ileum specimens were obtained to determine the tissue levels of malondialdehyde (MDA) and histological changes. RESULTS: The mucosal injury scores of group R were significantly higher than those of the group I (P<0.0001). The mucosal injury scores in the groups FR and MR were significantly lower than the group R (P<0.0001 and P<0.0001, respectively). In the group FR, mucosal injury scores were not significantly different from those of group I (P=0.123). However, mucosal injury scores of group MR were significantly less when compared to those of group I (P=0.01). Mean MDA levels of group R were significantly higher than those of the group I (P<0.0001). Mean MDA levels of groups FR and MR were significantly lower than those of group R (P<0.0001 and P<0.0001, respectively). In addition, MDA levels of group FR were significantly higher than those of group MR (P<0.0001). CONCLUSION: In conclusion, these observations suggest that the in vivo freezing of SMA and the pre-treatment with mannitol before reperfusion period may be useful in preventing intestinal reperfusion injury.

Animals↗
PubMed1999

Quantitative analysis of abducens neuron discharge dynamics during saccadic and slow eye movements.

The mechanics of the eyeball and its surrounding tissues, which together form the oculomotor plant, have been shown to be the same for smooth pursuit and saccadic eye movements. Hence it was postulated that similar signals would be carried by motoneurons during slow and rapid eye movements. In the present study, we directly addressed this proposal by determining which eye movement-based models best describe the discharge dynamics of primate abducens neurons during a variety of eye movement behaviors. We first characterized abducens neuron spike trains, as has been classically done, during fixation and sinusoidal smooth pursuit. We then systematically analyzed the discharge dynamics of abducens neurons during and following saccades, during step-ramp pursuit and during high velocity slow-phase vestibular nystagmus. We found that the commonly utilized first-order description of abducens neuron firing rates (FR = b + kE + r, where FR is firing rate, E and are eye position and velocity, respectively, and b, k, and r are constants) provided an adequate model of neuronal activity during saccades, smooth pursuit, and slow phase vestibular nystagmus. However, the use of a second-order model, which included an exponentially decaying term or "slide" (FR = b + kE + r + uE - c), notably improved our ability to describe neuronal activity when the eye was moving and also enabled us to model abducens neuron discharges during the postsaccadic interval. We also found that, for a given model, a single set of parameters could not be used to describe neuronal firing rates during both slow and rapid eye movements. Specifically, the eye velocity and position coefficients (r and k in the above models, respectively) consistently decreased as a function of the mean (and peak) eye velocity that was generated. In contrast, the bias (b, firing rate when looking straight ahead) invariably increased with eye velocity. Although these trends are likely to reflect, in part, nonlinearities that are intrinsic to the extraocular muscles, we propose that these results can also be explained by considering the time-varying resistance to movement that is generated by the antagonist muscle. We conclude that to create realistic and meaningful models of the neural control of horizontal eye movements, it is essential to consider the activation of the antagonist, as well as agonist motoneuron pools.

Abducens Nerve↗
PubMed1988

Fluence-response curves and action spectra for the very low fluence and the low fluence response for the induction of kalanchoë seed germination.

Germination of Kalanchoë blossfeldiana Poelln. seeds is absolutely light-requiring. Germination of one seed is the result of one out of three reactions, viz. the very low fluence response (VLFR), the low fluence response (LFR) and the high fluence response/high irradiance response. In order to demonstrate the involvement of phytochrome for both photoresponses, i.e. VLFR and LFR, action spectra for induction were determined. Fluence-response data are analyzed by means of probit analysis in order to calculate the seed population parameters, with special attention to mu, or the fluence for half-maximal induction, and B, the slope in the probit diagram. Laser light was used between 620 and 800 nanometers to analyze the VLFR. Phytochrome is responsible for both photoresponses: the VLFR action spectrum demonstrates an exponential decrease in apparent photoconversion cross-section (P(r) --> P(fr)) up to about 800 nanometers. Assuming that P(r):P(fr)-X and P(fr):P(fr)-X are the effectors for the VLFR and the LFR, respectively, we estimate an average induction threshold of about 0.003% P(r):P(fr) for the VLFR and about 1% P(fr):P(fr) for the LFR among individuals of the seed population.

Journal Article↗
PubMed1996

Phytochrome A enhances the promotion of hypocotyl growth caused by reductions in levels of phytochrome B in its far-red-light-absorbing form in light-grown Arabidopsis thaliana.

We sought to determine if phytochrome B (phyB)-mediated responses to the red light (R)/far-red light (FR) ratio are affected by phytochrome A (phyA) activity in light-grown seedlings of Arabidopsis thaliana. Pulses of FR delayed into the dark period were less effective than end-of-day (EOD) FR in promoting hypocotyl growth over a given period in darkness. White light minus blue light interposed instead of darkness between the end of the white-light photoperiod and the FR pulse was sufficient to maintain responsivity to the decrease in phyB in FR-light-absorbing form in wild-type (WT) seedlings, but not in the phyA mutant. Compared with EOD R, hourly R+FR pulses provided throughout the night caused a stronger promotion of stem growth than a single EOD R+FR pulse in WT Arabidopsis, cucumber, mustard, sunflower, tobacco, and tomato, but not in phyA Arabidopsis or in the aurea mutant of tomato. WT seedlings of Arabidopsis responded to a range of high EOD R/FR ratios, whereas the phyA mutant required stronger reductions in the EOD R/FR ratio. In sunlight, phyA seedlings of Arabidopsis showed no response to the "early warning" signals of neighboring vegetation, and hypocotyl-growth promotion occurred at higher plant densities than in the WT. Thus, under a series of light conditions, the sensitivity or responsivity to reductions in the R/FR ratio were larger in WT than in phyA seedlings. A product of phyA is therefore proposed to enhance the hypocotyl-growth response to decreases in phyB in FR-light-absorbing form in light grown seedlings.

Arabidopsis↗
PubMed2003

Understory light and root ginsenosides in forest-grown Panax quinquefolius.

The objective of this study was to determine the relationship between light levels in the understory of a broadleaf forest and the content of six ginsenosides (Rg(1), Re, Rb(1), Rc, Rb(2,) and Rd) in 1- and 2-year-old American ginseng (Panax quinquefolius L.) roots. Our results revealed that ginsenoside contents in 1- and 2 year-old roots collected in September were significantly related to direct and total light levels, and duration of sunflecks. At this time, the effect of light levels accounted for up to 48 and 62% of the variation in ginsenoside contents of 1- and 2-year-old American ginseng roots. Also, red (R) and far red (FR) light, and the R:FR ratio significantly affected Rd, Rc, and Rg(1) contents in 2-year-old roots, accounting for up to 40% of the variation in ginsenoside contents.

Ginsenosides↗
PubMed1991

The spectral distribution of biologically active solar radiation at Miami, Florida, USA.

The spectral distribution of solar radiation was studied under different sky conditions during a 15-month period in Miami, Florida (USA), and over a latitudinal gradient at solar maximum. Spectroradiometric scans were characterized for total irradiance (300-3000 nm) and the relative energetic and photon contributions of the following wavelength regions: UV-B (300-320 nm); UV-A (320-400 nm); B (400-500 nm); PAR (400-700 nm); R (600-700 nm); and FR (728-732 nm). Notable results include: (i) significantly higher UV-A energy fluxes than currently in use for laboratory experiments involving the biological effects of this bandwidth (values ranged from 33.6 to 55.4 W/m2 in Miami over the year); (ii) marked diurnal shifts in B:R and R:FR, with elevated R:FR values in early morning: (iii) a strong correlation between R:FR and atmospheric water content; and (iv) unusually high PAR values under direct sunlight with cloudy skies (2484 mumol/2 per s).

Cosmic Radiation↗
PubMed2003

Dimerization and inter-chromophore distance of Cph1 phytochrome from Synechocystis, as monitored by fluorescence homo and hetero energy transfer.

We investigated the dimerization of phytochrome Cph1 from the cyanobacterium Synechocystis by fluorescence resonance energy transfer (FRET). As donor we used the chromophore analogue phycoerythrobilin (PEB) and as acceptor either the natural chromophore phycocyanobilin (PCB; hetero transfer) or PEB (homo transfer). Both chromophores bind in a 1:1 stoichiometry to apo-monomers expressed in Escherichia coli. Energy transfer was characterized by time-resolved fluorescence intensity and anisotropy decay after excitation of PEB by picosecond pulses from a tunable Ti-sapphire laser system. ApoCph1 was first assembled with PEB at a low stoichiometry of 0.1. The remaining sites were then sequentially titrated with PCB. In the course of this titration, the mean lifetime of PEB decreased from 3.33 to 1.25 ns in the P(r) form of Cph1, whereas the anisotropy decay was unaffected. In the P(fr)/P(r) photoequilibrium (about 65% P(fr)), the mean lifetime decreased significantly less, to 1.67 ns. These observations provide strong support for inter-chromophore hetero energy transfer in mixed PEB/PCB dimers. The reduced energy transfer in P(fr) may be due to a structural difference but is at least in part due to the difference in spectral overlap, which was 4.1 x 10(-13) and 1.6 x 10(-13) cm(3) M(-1) in P(r) and P(fr), respectively. From the changes in the mean lifetime, rates of hetero energy transfer of 0.68 and 0.37 ns(-1) were calculated for the P(r) form and the P(fr)/P(r) photoequilibrium, respectively. Sequential titration of apo Cph1 with PEB alone to full occupancy did not affect the intensity decay but led to a substantial increase in depolarization. This is the experimental signature of homo energy transfer. Values for the rate of energy transfer k(HT) (0.47 ns(-1)) and the angle 2theta between the transition dipole moment directions (2theta = 45 +/- 5 degrees) were determined from an analysis of the concentration dependence of the anisotropy at five different PEB/Cph1 stoichiometries. The independently determined rates of hetero and homo energy transfer are thus of comparable magnitude and consistent with the energy transfer interpretation. Using these results and exploiting the 2-fold symmetry of the dimer, the chromophore-chromophore distance R(DA) was calculated and found to be in the range 49 A < R(DA) < 63 A. Further evidence for energy transfer in Cph1 dimers was obtained from dilution experiments with PEB/PEB dimers: the lifetime was unchanged, but the anisotropy increased as the dimers dissociated with increasing dilution. These experiments allowed a rough estimate of 5 +/- 3 microM for the dimer dissociation constant. With the deletion mutant Cph1Delta2 that lacks the carboxy terminal histidine kinase domain less energy transfer was observed suggesting that in this mutant dimerization is much weaker. The carboxy terminal domain of Cph1 that is involved in intersubunit trans-phosphorylation and signal transduction thus plays a dominant role in the dimerization. The FRET method provides a sensitive assay to monitor the association of Cph1 monomers.

Bacterial Proteins↗
PubMed1981

Phytochrome Control of Maize Coleoptile Section Elongation : A RAPID LOSS OF PHOTOREVERSIBILITY.

A rapid loss of far red light (FR) reversibility of red-light (R) stimulated elongation of maize coleoptile sections was observed. Reversal was not possible when the interval between R and FR treatment was greater than 45 seconds. Most of the R-stimulated elongation occurred during the first 15 hours after irradiation.Exogenous gibberellic acid did not alter the time course of R/FR reversibility loss. These results are interpreted as indicating independence of R- and gibberellic acid-stimulated elongation in this system.

Journal Article↗
PubMed1970

Immunochemical and spectroscopic evidence for protein conformational changes in phytochrome transformations.

Phytochrome was examined by immunochemical and spectroscopic techniques to detect differences between the protein moieties of red- and far red-absorbing phytochrome (P(r) and P(fr)). No differences in the reaction of P(r) and P(fr) with phytochrome antibody were discernible on Ouchterlony double diffusion plates. However, the microcomplement fixation assay showed a greater degree of antibody reaction with P(fr) than with P(r), indicating some difference in the surface characteristics of the two forms. Circular dichroism spectroscopy between 300 and 200 nanometers revealed differences between P(r) and P(fr) which may reflect differences in the protein conformation. The circular dichroism spectrum of P(r) showed a negative band at 285 nanometers which was not present in the spectrum of P(fr), and the large negative circular dichroism band at 222 nanometers with P(fr), associated with the alpha-helical content, was shifted 2 nanometers to shorter wave length with P(r) although there was no change of magnitude of this band. The absorbancy of P(r) and P(fr) is very nearly the same in the 280 nanometer spectral region, but sensitive difference spectra between P(r) and P(fr) did reveal spectra which were similar to solvent perturbation spectra obtained by others with different proteins. In total, the experiments indicate that there are conformational differences between the protein moieties of P(r) and P(fr) but that these differences are rather slight from a standpoint of gross structure.

Journal Article↗
PubMed1985

Mode of coaction between blue/UV light and light absorbed by phytochrome in light-mediated anthocyanin formation in the milo (Sorghum vulgare Pers.) seedling.

Anthocyanin formation in milo (Sorghum vulgare Pers.) seedlings (coleoptile, mesocotyl, taproot) occurs only in white light and blue/UV light (BL/UV), while red light (RL) and far-RL are totally ineffective. However, after a BL/UV pretreatment, the participation of phytochrome can be demonstrated. With a short-wavelength light source [peak emission in longwave UV (UV-A)], the mode of coaction between BL/UV and light absorbed by phytochrome (RL) was studied with the following principal results. (i) As soon as the seedling becomes competent to respond to UV-A (with regard to anthocyanin formation), the involvement of phytochrome can be detected. (ii) A 5-min pulse of UV-A has a strong effect on the anthocyanin synthesis in the milo mesocotyl. This effect is fully reversible if a long-wavelength far-RL pulse (RG9 light) is given immediately after the UV-A light pulse. (iii) When seedlings treated with 5 min of UV-A and 5 min of RG9 light are kept in darkness for 3 hr and then transferred to RL, anthocyanin appears. (iv) In continuous UV-A treatment, anthocyanin accumulation starts after a lag phase of 3.5 hr (25 degrees C). A RL pretreatment prior to the onset of UV-A treatment strongly increases anthocyanin accumulation in UV-A, though the lag phase is not affected. Moreover, a RL pretreatment does not affect the time course for escape from reversibility in UV-A. It is concluded from these data that BL/UV cannot mediate induction of anthocyanin synthesis in the absence of P(fr), the active form of phytochrome that absorbs maximally in the far-red. Rather, the action of BL/UV must be considered to establish responsiveness of the anthocyanin-producing mechanism to P(fr). P(fr) operates in this system via two different channels. As the effector of the terminal response, it sets in motion the signal-response chain that eventually leads to the appearance of anthocyanin. This is a slow process with a lag phase of the order of 3.5 hr. The second function of P(fr) is to determine the responsiveness to the effector P(fr) in mediating anthocyanin synthesis. This is a very fast and highly sensitive phytochrome action that can be detected readily within 1 min. However, as long as the plant has not received BL/UV, the strong effect of RL on the effectiveness of P(fr) remains cryptic. The effect of a RL pretreatment and the effect of a UV-A pretreatment on responsiveness towards P(fr) (or, effectiveness of P(fr)) were found to be totally independent of each other, even though it is the UV-A that permits operation of P(fr).

Journal Article↗
PubMed1991

Resolution and characterization of pro-B and pre-pro-B cell stages in normal mouse bone marrow.

We have resolved B220+ IgM- B-lineage cells in mouse bone marrow into four fractions based on differential cell surface expression of determinants recognized by S7 (leukosialin, CD43), BP-1, and 30F1 (heat stable antigen). Functional differences among these fractions can be correlated with Ig gene rearrangement status. The largest fraction, lacking S7, consists of pre-B cells whereas the others, expressing S7, include B lineage cells before pre-B. These S7+ fractions, provisionally termed Fr. A, Fr. B, and Fr. C, can differentiate in a stromal layer culture system. Phenotypic alteration during such culture suggests an ordering of these stages from Fr. A to Fr. B to Fr. C and thence to S7- pre-B cells. Using polymerase chain reaction amplification with pairs of oligonucleotide primers for regions 5' of JH1, DFL16.1, and Jk1, we find that the Ig genes of Fr. A are in germline configuration, whereas Fr. B and C are pro-B cell stages with increasing D-J rearrangement, but no V-D-J. Finally, functional analysis demonstrates that the proliferative response to IL-7, an early B lineage growth factor, is restricted to S7+ stages and, furthermore, that an additional, cell contact-mediated signal is essential for survival of Fr. A.

Animals↗
PubMed1968

Phytochrome and Seed Germination. IV. Action of Light Sources With Different Spectral Energy Distribution on the Germination of Tomato Seeds.

Germination of tomato seeds exposed to a single, saturating irradiation from light sources of different spectral energy distribution seems to be dependent upon the photostationary P(FR)/P(R) ratio established by the irradiation. Germination of tomato seeds exposed to prolonged irradiations from the same light sources does not seem to be controlled solely by the P(FR)/P(R) ratio induced and maintained by the irradiation.

Journal Article↗
PubMed2001

Light-induced proton release and proton uptake reactions in the cyanobacterial phytochrome Cph1.

The P(r) to P(fr) transition of recombinant Synechocystis PCC 6803 phytochrome Cph1 and its N-terminal sensor domain Cph1Delta2 is accompanied by net acidification in unbuffered solution. The extent of this net photoreversible proton release was measured with a conventional pH electrode and increased from less than 0.1 proton released per P(fr) formed at pH 9 to between 0.6 (Cph1) and 1.1 (Cph1Delta2) H(+)/P(fr) at pH 6. The kinetics of the proton release were monitored at pH 7 and pH 8 using flash-induced transient absorption measurements with the pH indicator dye fluorescein. Proton release occurs with time constants of approximately 4 and approximately 20 ms that were also observed in parallel measurements of the photocycle (tau(3) and tau(4)). The number of transiently released protons per P(fr) formed is about one. This H(+) release phase is followed by a proton uptake phase of a smaller amplitude that has a time constant of approximately 270 ms (tau(5)) and is synchronous with the formation of P(fr). The acidification observed in the P(r) to P(fr) transition with pH electrodes is the net effect of these two sequential protonation changes. Flash-induced transient absorption measurements were carried out with Cph1 and Cph1Delta2 at pH 7 and pH 8. Global analysis indicated the presence of five kinetic components (tau(1)-tau(5): 5 and 300 micros and 3, 30, and 300 ms). Whereas the time constants were approximately pH independent, the corresponding amplitude spectra (B(1), B(3), and B(5)) showed significant pH dependence. Measurements of the P(r)/P(fr) photoequilibrium indicated that it is pH independent in the range of 6.5-9.0. Analysis of the pH dependence of the absorption spectra from 6.5 to 9.0 suggested that the phycocyanobilin chromophore deprotonates at alkaline pH in both P(r) and P(fr) with an approximate pK(a) of 9.5. The protonation state of the chromophore at neutral pH is therefore the same in both P(r) and P(fr). The light-induced deprotonation and reprotonation of Cph1 at neutral pH are thus due to pK(a) changes in the protein moiety, which are linked to conformational transitions occurring around 4 and 270 ms after photoexcitation. These transient structural changes may be relevant for signal transduction by this cyanobacterial phytochrome.

Bacterial Proteins↗