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Biomedical subjects

J Barber

Publications and source records attributed to J Barber.

At least 253 records · Page 14Linked to original sources
PubMed1977

Picosecond laser study of fluorescence lifetimes in spinach chloroplast photosytem I and photosystem II preparations.

Fractions enriched in either Photosystem I or Photosystem II have been prepared from chloroplasts with digitonin. A more detailed analysis of the decay kinetics of fluorescence excited by a picosecond laser pulse has been possible compared to experiments with unfractionated systems. The Photosystem I fractions show a very short component (less than or equal to 100 ps) at room temperature which is apparently independent of pulse intensity over the range of photon densities used (5 - 10(13)--1 - 10(16) photons cm-2). The Photosystem II fraction has a short initial lifetime at room temperature which is strongly intensity-dependent approaching 500 ps at low photon densities, but decreasing to close to 150 ps at the highest photon densities. All of these room temperature decays appear to be non-exponential, and may possibly be fitted by at t1/2 expression, expected from a random diffusion of excitations via Förster energy transfer. On cooling to 77K, lifetimes of both Photosystem I and Photosytem II increase, the lengthening with Photosystem I being more striking. The Photosystem I decays become intensity dependent like the Photosystem II, and at the lowest photon densities decays which are more nearly exponential within the experimental error give initial lifetimes of about 2 ns. The non-exponential decays seen at high photon densities appear to fit a t1/2 expression.

Chloroplasts↗
PubMed1977

Psychological, physiological, and pharmacological management of pain.

It has been the intent of the authors to impress upon the clinician the multifaceted nature of the human pain experience. We have sought to create an understanding of the emotional nature of pain. The treatment of pain as a pure sensation without directing attention to its behavioral and psychological aspects will generally lead to failure in understanding and ultimately in treating this ubiquitous problem in our profession. The use of drugs alone will have only a minor effect on the treatment of pain. Knowledge of environmental control and an understanding and empathetic approach to the patient in pain or in stress will carry the dentist a long way toward his goal of dental treatment without pain or emotional upset.

Age Factors↗
PubMed1977

Hypnosis and suggestion for fitting contact lenses.

Language is important in the creation of a painful or non-painful context for fitting contact lenses. This article discusses two types of language use and demonstrates the consequent experience each creates for the patient. The authors also emphasize the importance of acceptance and utilization of responses offered by the patient to further the goals of a comfortable fitting experience. Finally, this article provides an example of a reliable and successful technique for rapidly inducing hypnosis for the purpose of obtaining a comfortable lens fitting.

Communication↗
PubMed1976

Fluorescence lifetimes of Chlorella pyrenoidosa.

The flucrescence decay of Chlorella pyrenoidosa has been investigated under a variety of conditions in the picosecond and nanosecond time regions. Most of the fluorescence is accounted for by an expression of the form I(t) = I0exp-(At+Bt1/2) though an additional exponential term is required to include a weak component of lifetime 32 ps observable only at the higher pulse intensities. This interpretation reconciles earlier and apparently conflicting data. The weak 32 ps component may be associated with Photosystem I, although the possibility that it is an artefact of the high intensity pulses used cannot be excluded at present. The main fluorescence, described by the equation above is attributed to the antenna chlorophyll and is of the form which would be expected from a single light harvesting array with trapping at randomly distributed sites.

Chlorella↗
PubMed1976

Cation control of chlorophyll a fluorescence yield in chloroplasts. Location of cation sensitive sites.

We have compared the effect of various cations on the fluorescence yield of chloroplasts under several different conditions in vitro. 1. In the absence of a high energy state but in the presence of low (10 mM) concentrations of monovalent cations, divalent metal cations increase steady state chlorophyll a fluorescence yield in a manner which does not involve transport of these cations across the thylakoid membranes. 2. The kinetics of this cation-induced fluorescence rise are relatively slow, and seem to reflect cation binding (or subsequent conformational changes) to sites on the outer surface of the thylakoid membrane. 3. In the absence of monovalent cations, the apparent binding constant for Mg2+ to sites on the outer side of the membrane is low. Addition of low concentrations of monovalent cations (10 mM) competitively inhibits divalent cation binding. 4. Control of fluorescence yield is also exerted by the high energy state, and seems to involve proton/metal cation exchange at sites on the inner side of the thylakoid. 5. When isolated chloroplasts are washed and resuspended in a medium containing no added cations, the initial fluorescence level is high, but is quenched on addition of monovalent cations, sodium EDTA being much more effective than sodium chloride. It is argued that when isolated under these conditions, chloroplasts retain sufficient divalent cations to saturate external negative sites, and that the fluorescence lowering is due to their removal. 6. Some other cations, such as poly(L-lysine), can displace divalent cations from their external sites in an irreversible manner, resulting in a fixed low fluorescence yield.

Binding, Competitive↗
PubMed1976

Enhancement studies on algae and isolated chloroplasts. Part II. Enhancement of oxygen evolution in intact chloroplasts.

Intact isolated chloroplasts were shown to exhibit a characteristic three-phase pattern of development of oxygen evolution activity. The first phase, Phase I, appeared to be an equilibration phase in which the isolated chloroplasts adapted to the conditions on the electrode surface. It was characterised by a rapidly increasing rate of oxygen evolution accompanied by decreasing enhancement signals. The second phase, Phase II, was an intermediate phase in which the rate of oxygen evolution was maximal and no enhancement was observed. In the last phase, Phase III, the rate of oxygen fell again, normal enhancement was still missing, but the samples appeared to undergo slow adaptive changes closely related to the State I-State II changes previously reported for whole cell systems. The concentrations of Mg2+ within the chloroplast were shown to play an important role in the control of the development of both the oxygen evolution and enhancement signals. It was shown how these signals could be explained in terms of a model that was consistent with that developed in Part I of this investigation to account for the variability of enhancement of the alga Chlorella pyrenoidosa.

Chlorella↗
PubMed1976

The pharmacokinetics of chlormethiazole following intravenous administration in the aged.

Eight healthy aged subjects were administered 1.2 g of chlormethiazole by constant-rate intravenous infusion. The disposition of the drug was found to be multi-exponential in character. Fits of plasma level-time data to two- and three-compartment open models were assessed with the aid of statistical tests. For three of the subjects the experimental data were adequately fitted to a two-compartment pharmakcokinetic model, however a three-compartment model was necessary to fit the data observed for a further four subjects. An anomalous chlormethiazole plasma concentration-time curve was obtained for the remaining subject. The disposition half-life of chlormethiazole was 8.49 +/- 3.28 h and the plasma clearance was 16.14 +/- 5.00 ml/min/kg. These values were significantly different to those reported earlier for young adult subjects and the clinical implications have been discussed. The blood/plasma concentration ratio of chlormethiazole was found to be approximately one with some evidence for concentration dependence.

Aged↗
PubMed1975

Availability of monovalent and divalent cations within intact chloroplasts for the action of ionophores nigericin and A23187.

1. A23187 will uncouple electron transport by broken chloroplasts in a divalent cation dependent manner provided that they have been treated with a low concentration of EDTA. 2. A23187 stimulates oxaloacetate-dependent oxygen evolution and inhibits phosphoglycerate reduction by intact chloroplasts isolated in a cation-free medium whereas the full effect of nigericin was dependent on the presence of external K+. 3. Uncoupling of oxaloacetate reduction by A23187 in intact chloroplasts is inhibited by EDTA and this effect is overcome by excess Mg2+. 4. The results suggest that divalent and not monovalent cations are available for collapsing the light-induced H+ gradient within the intact organelle.

Anti-Bacterial Agents↗