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PubMed1978

The double flash ERG during adaptation to the dark.

Electroretinogram (ERG) of albino rabbits and rheusus monkeys were recorded in a dark room applying the double flash stimuli after a sufficient adaptation to light. The stimulus intervals of the flashes were varied. The per cent amplitudes of the ERGs for the first flashes (B1) and those of the second flashes (B2) were plotted against time, as was (B1-B2)/B1 (=K). 1. B1 was independent of the stimulus interval in both species, and increased with lapse of time to reach a plateau. 2. B2 was quite dependent on the stimulus interval, and the ERG dark adaptation curves of the two species were quite different. 3. The time course of (B1-B2)/B1 was specific for the two species. In the rabbit, Ks were almonst equal for three stimulus intervals during states of adaptation to complete darkness, and in the monkey, Ks were different for the three intervals under all conditions.

Animals↗

PubMed1979

LH, FSH and skin temperaure during the menopausal hot flash.

Six postmenopausal women, who were experiencing frequent hot flashes, had an 8 h continuous recording of skin temperature over the dorsum of the finger as an objective index of hot flashes. Frequent blood samples were obtained during the time of the recording for the measurement of serum luteinizing hormone (LH) and follicle-stimulating hormone (FSH) levels. During the 48 h of recording 34 significant temperature elevations were recorded and 32 were associated with a subjective hot flash. 3l pulses of LH release were also observed with 26 occurring simultaneously with the temperature rises. Correlation analysis of simultaneous skin temperature and circulating LH levels showed a significant positive correlation (p less than 0.01). FSH levels showed no consistent relationship with skin temperature. These data suggest that LH or the factors that trigger its pulsatile release are related to the mechanism responsible for the initiation of hot flashes.

Climacteric↗

PubMedDate not supplied

Responses of barnacle photoreceptors to high energy flashes of short duration.

In chromatic adapted barnacle median and lateral photoreceptors the two stable states of the photopigment (rhodopsin R and metarhodopsin M) were interconverted with intense, colored light flashes of 1 ms duration. Only after conversion of the red adapted photoreceptor in K+-Ringer solution with an intense flash the negative early receptor potential, ERP (of R) gradually appeared detected with an indicator flash. For the opposite conversion (blue adapted, R leads M) the gradual appearance of the positive ERP (M) was not measurable in the same time span. In artificial seawater all flash stimuli yielded--irrespective of color--the transient component of the late receptor potential (LRP). ERP results for the lateral photoreceptor are discussed in view of an existing kinetic model and an attempt is made to give an explanation which covers the new LRP transient and ERP results for both types of photoreceptor (appendix).

Animals↗

PubMed1975

Effect of preconditioning visual stimulus duration on visual-evoked responses to a subsequent test flash in Down's syndrome and nonretarded individuals.

Visual-evoked responses to a visual test flash preceded by three different durations of a visual conditioning flash having the same intensity and form were recorded from 8 Down's syndrome subjects and 9 nonretarded CA-matched control subjects. Both groups showed a significant decrease in visual-evoked response perimeters to the test flash as the duration of the visual conditioning flash increased from 1 to 100 msec. For the 1000-msec condition, perimeters of Down's syndrome subjects showed a significant increase, and this was significantly greater than the nonretarded group. These results suggest that Down's syndrome individuals have deficits in their neural processing of sensory information.?23Author

Adolescent↗

PubMed1979

Pattern and flash visual evoked responses in multiple sclerosis.

In multiple sclerosis (MS), increase of delay may be important, but the earlier change is the behavior of the wave shape; amplitude is always lower even in MS patients without visual subjective symptomatology, provided not only flash but also pattern stimulation is performed. Normal amplitude with pattern stimulation does not necessarily mean normal with flash. Combining both stimulation methods, we obtained lowering of amplitude and change of wave shape in 100% of cases while latency was increased in only 77% of cases. Sectorial ischemic neuropathy, and open angle glaucoma patients show the same findings, which emphasizes that the method is not specific for demyelinating diseases, nor selective for papillomacular bundle involvement, but that VER, considering only its first components, reflects axonal damage somewhere in the visual pathway. Flash and pattern VER might be even more pathognomonic in MS than oligoclonal gammaglobulin fractionation on agar, positive in 75% of cases. It is suggested that subclinical MS cases should be submitted to full electro-ophthalmographic investigation.

Form Perception↗

PubMed1978

Flash photolysis of rhodopsin in rabbit.

Flash photolysis of rhodopsin in rabbit's retina has been analysed theoretically, and the results are found to be in good agreement with the experimental results of Hagins (1957). We have also obtained the variation of relative concentrations of rhodopsin, lumirhodopsin, isorhodopsin and metarhodopsin I during the period of the flash corresponding to two different intensities of the flash. It has been found that the quantum efficiencies of conversion of lumirhodopsin into rhodopsin and isorhodopsin will lie in the range 0.24--0.45 and 0.20--0.44 respectively; quantum efficiency of conversion of metarhodopsin I into rhodopsin and isorhodopsin are found to have values greater than 0.52 and 0.45 respectively and the quantum efficiency of conversion of isorhodopsin into lumirhodopsin has been found to be approximately 0.865. Also the maximum value of the rate constant of the reaction metarhodopsin I leads to metarhodopsin II at 37 degrees C has been determined in decerebrated eye and it has been found that it is of the same order as found by Pugh (1975) in the case of human eye.

Animals↗

PubMed1979

Elevations in skin temperature of the finger as an objective index of postmenopausal hot flashes: standardization of the technique.

The present study was designed to validate and standardize a technique of continuous recording of skin temperature of the finger as an objective index of hot flashes. Significant skin temperature rises (greater than 1 degree C) were recorded in close temporal relationship to 69% of subjective hot flashes experienced by seven postmenopausal women. The temperature elevations occurred at an interval of 54 +/- 10 minutes (mean +/- standard error) and lasted an average of 31 minutes. The mean increase was 2.7 degrees +/- 0.2 degrees C. The extent of the temperature elevations found in the postmenopausal subjects was significantly greater than in premenopausal control subjects (P less than 0.05) and was reduced by estrogen treatment (P less than 0.02). This study substantiates that the recording of skin temperature changes of the finger provides an objective index of hot flashes. This should assist in the investigation of the underlying disturbance and provide more accurate evaluation of modes of therapy.

Adult↗

PubMed1975

Electrical potential changes, H+ translocation and phosphorylation induced by short flash excitation in Rhodopseudomonas sphaeroides chromatophores.

1. The basal decay of the carotenoid shift of chromatophores from photosynthetic bacteria following short flash excitation is approximately biphasic. The decay indicates the dissipation of the transmembrane electrical potential. 2. The H+ efflux following rapid H+ binding after a flash, measured from the colour change of added cresol red, shows very similar kinetics to the carotenoid shift decay suggesting that the dissipation of the electric potential decay is a consequence of the H+ efflux. 3. The electric potential decay is stimulated when the chromatophore suspension is supplemented with ADP and Pi (in either the presence or absence of antimycin A). 4. The stimulated electric potential decay by ADP and Pi has a similar pH dependence to that of phosphorylation in continuous light. 5. The stimulation of the electric potential decay by ADP and Pi is reversed, by aurovertin, an antibiotic which inhibits phosphorylation. 6. The stimulation of the electric potential decay by ADP+Pi is also reversed by the inhibitors oligomycin and venturicidin. These inhibitors, but not aurovertin, also inhibit the fast phase of the decay under non-phosphorylating conditions. 7. Valinomycin accelerates the overall rate of decay of the electric potential, inhibits the ADP and Pi stimulated electric potential decay, and inhibits the flash-induced phosphorylation. The decay rate of the H+ efflux however, is slower in the presence of this ionophore. 8. Nigericin-type ionophores accelerate the overall decay rate of the H+ efflux and inhibit the ADP and Pi stimulated electric potential decay. The basal rate of the electric potential decay is unaffected by treatment with these ionophores. 9. When a coupling factor associated with the chromatophore ATPase is removed from the membrane, both the stimulation of the electric potential decay by ADP and Pi and ADP phosphorylation are inhibtied. Both reactions are completely restored after reconstitution with the crude coupling factor extract. The basal electric potential decay rate is not affected by the removal of coupling factor.

Adenosine Diphosphate↗

PubMed1976

Determination of H+/e- ratios in chloroplasts with flashing light.

Using a rapid pH electrode, measurements were made of the flash-induced proton transport in isolated spinach chloroplasts. To calibrate the system, we assumed that in the presence of ferricyanide and in steady-state flashing light, each flash liberates from water one proton per reaction chain. We concluded that with both ferricyanide and methylviologen as acceptors two protons per electron are translocated by the electron transport chain connecting Photosystem II and I. With methyl viologen but not with ferricyanide as an acceptor, two additional protons per electron are taken up due to Photosystem I activity. One of these latter protons is translocated to the inside of the thylakoid while the other is taken up in H2O2 formation. Assuming that the proton released during water splitting remains inside the thylakoid, we compute H+/e- ratios of 3 and 4 for ferricyanide and methylviologen, respectively. In continuous light of low intensity, we obtained the same H+/e- ratios. However, with higher intensities where electron transport becomes rate limited by the internal pH, the H+/e- ratio approached 2 as a limit for both acceptors. A working model is presented which includes two sites of proton translocation, one between the photoacts, the other connected to Photosystem I, each of which translocates two protons per electron. Each site presents a approximately 30 ms diffusion barrier to proton passage which can be lowered by uncouplers to 6-10 ms.

Chloroplasts↗

PubMed1977

Ubiquinone reduction and proton uptake by chromatophores of Rhodopseudomonas sphaeroides R-26: periodicity of two in consecutive light flashes.

Chromatophores of Rhodopseudomonas sphaeroides strain R-26 were subjected to a series of brief flashes of light in the presence of diaminodurene as an electron donor. Odd-numbered flashes induced the reduction of ubiquinone to the anionic semiquinone, as indicated by absorbance changes near 450 nm. This reaction was not attended by proton binding. Even-numbered flashes caused disappearance of the semiquinone, presumably by conversion to the fully reduced form. This reaction was attended by proton uptake.

Bacterial Chromatophores↗

PubMed1979

The buffering capacity of the internal phase of thylakoids and the magnitude of the pH changes inside under flashing light.

The buffering capacity inside thylakoids is determined and the magnitude of flash-induced pH changes inside is calibrated in the pH range from 6.4 to 8.1. The work is based on flash-induced absorption changes of neutral red in a chloroplast suspension in which the outer phase is strongly buffered by bovine serum albumin. It is shown that neutral red is bound inside thylakoids. The binding can be described by a simple isotherm with an apparent Km = 4 microM and satruation at 1 neutral red per 17 chlorophylls. The apparent pK of neutral red is shifted from 6.6 in solution to 7.25 when bound inside. It is demonstrated that neutral red is a clean indicator of pH changes inside, i.e. when properly used it shows no response to other events. Although bound it reports pH changes which occur in the internal osmolar (aqueous) volume of thylakoids. This is obvious from the influence of chemically very different buffers on the magnitude of the absorption changes of neutral red. These act in a manner proportional to their calculated buffering capacity in aqueous solution. The intrinsic buffering capacity of the internal phase is determined with the aid of these buffers, at pH 7.2 it is between 0.8 and 1 mM (at 60 mosM). The absence of large variations in the buffering capacity in the range from pH 6.4 to 8.1 suggests that proteinaceous groups are involved in addition to the lipids which may dominate the buffering capacity at lower pH. The magnitude of the internal pH change is arrpox. 0.6 (at pH 7.3) under stimulation of both photosystems with a short xenon flash of light.

Chloroplasts↗

PubMed1979

Hemisphere differences and judgments of simultaneity of brief light flashes.

A series of experiments was conducted to investigate the possibility of hemispheric specialization for judgments of the simultaneity of two light flashes. Right-handed subjects adjusted two light flashes until they appeared simultaneous. The comparison of measures derived from the two possible orders of the light flashes suggested that the right hemisphere of right-handed subjects performed the function of ordering visual stimuli in time. Two further experiments examined an alternative explanation, that of a left-to-right scanning mechanism, the results of which also suggested a hemisphere explanation. The results of these experiments are discussed in terms of previous research and theories which located a temporal ordering mechanism in the speech hemisphere.

Adolescent↗

PubMedDate not supplied

[Study of electron transport in the photosynthetic systems of higher plants by the ESR method. VI. Kinetics of photo-induced P700 redox transitions in a system of continuous and flash illumination of different duration].

The kinetics of P700 redox-transients in leaves and isolated been and spinach chloroplasts was studied by the ESR method. P700 oxidation after a short flash (less than 10 microseconds) of white light was not resolved. P700 oxidation may be resolved only after "long" (more than 500 microseconds) flash of red light (700 or 720 nm) with a slow reduction of P700+ in the dark. In case of 500 microseconds flash exciting both photosystems (600 nm) P700 response was not observed. Fast P700+ reduction was observed if the short pulse of white light was given simultaneously with a continuous background 707 nm light. We can conclude from these data that P700+ accepts an electron from its primary donor within 10--500 microseconds.

Chloroplasts↗

PubMed1979

Pattern and flash evoked responses in disseminated and selective optic pathway damage.

In multiple sclerosis (MS), an increase in delay in visual evoked responses (VER) may be important, but an earlier change is the behaviour of the wave-shape; amplitude is always lower even in MS patients without subjective visual symptoms, provided not only flash but also pattern stimulation is used. Normal amplitude with pattern stimulation does not necessarily mean normal amplitude with flash stimulation. Combining both stimulation methods, we found lowering of amplitude and change of wave-shape in 100 per cent of cases while latency was increased in only 77 per cent. Flash and pattern VER might be even more pathognomonic in MS than oligoclonal gammaglobulin fractionation on agar, which is positive in 75 per cent of cases. We recommend that subclinical cases of MS should be submitted to full electro-oculographic investigation. Patients with sectoral ischaemic neuropathy and open angle glaucoma (OAG) show the same findings; this emphasizes that the method is not specific for demyelinating diseases, nor selective for papillo-macular bundle involvement, but that VER, considering only its first components, reflects axonal damage somewhere in the visual pathway.

Evoked Potentials↗

PubMed1978

Corneal wick electrode for recording bright flash electroretinograms and early receptor potentials.

We developed a corneal wick electrode that is free of photovoltaic artifact when used with a bright flash strobe and is convenient for routine clinical application. The corneal wick electrode is employed for bright flash electroretinogram (ERG) recordings and for research measurements of the early receptor potential. The wick electrode gives accurate, stable, reproducible recordings with an amplitude comparable to that obtained with standard contact lens electrodes.

Action Potentials↗

PubMed1979

Quantitative flash-methylation analysis of phenobarbital.

In phenobarbital measurement by GLC with the flash-methylation technique, using trimethylanilinium hydroxide as a methylating reagent, a small amount of water decomposed phenobarbital and interfered with the quantitative analysis. Thus, both the sample and the methylating reagent must be sufficiently dehydrated to attain quantitative analyses. The hydrolysis decomposition product of phenobarbital was N-methyl-2-phenylbutyramide, as shown by its mass spectrum. The sum of methylated phenobarbital and N-methyl-2-phenylbutyramide (if observed in the spectrum) can be used for an accurate phenobarbital assay in the present flash-methylation technique.

Chromatography, Gas↗

PubMed1975

Delayed fluorescence from Rhodopseudomonas viridis following single flashes.

Delayed fluorescence from Rhodopseudomonas viridis membrane fragments has been studies using a phosphoroscope employing single, short actinic flashes, under conditions of controlled redox potential and temperature. The emission spectrum shows that delayed fluorescence is emitted by the bulk, antenna bacteriochlorophyll. The energy for delayed fluorescence, however, must be stored in a reaction-center complex including the photooxidized form (P+) of the primary electron-donor (P) and the photoreduced form (X MINUS) of the primary electron-acceptor. This is shown by the following observations: (1) Delayed luminescence is quenched (a) at low redox potentials which allow cytochromes to reduce P+ rapidly after the flash, (b) at higher redox potentials which, by oxidizing P chemically, prevent the photochemical formation of P+X minus, and (c) upon transfer of an electron from X minus to a secondary acceptor, Y. (2) Under conditions that prevent the reduction of P+ by cytochromes and the oxidation of X minus by Y, the decay kinetics of delayed fluorescence are identical with those of P+X minus, as measured from optical absorbance changes. The main decay route for P+X minus under these conditions has a rate-constant of approximately 10-3-s-minus 1. In contrase, a comparison of the intensities of delayed and prompt fluorescence indicates that the process in which P+X minus returns energy to the bulk bacteriochlorophyll has a rate-constant of 3.7 s-minus 1, at 295 degrees K and pH 7.8. The decay kinetics of P+X minus and delayed fluorescence change little with temperature, whereas the intensity of delayed fluorescence increases with increasing temperature, having an activation energy of 12.5 kcal mol-mol- minus 1. We conclude that the main decay route involves tunneling of an electron from X minus to P+, without the promotion of P to an excited state. Delayed fluorescence requires such a promotion, followed by transfer of energy to the bulk bacteriochlorophyll, and this combination of events is rare. The activation energy, taken with potentiometric data, indicates that the photochemical conversion of PX to P+X minus results in increases of both the energy and the entropy of the system, by 16.6 kcal-mol- minus 1 and 8.8 cal-mol- minus 1-deg- minus 1. The intensity of delayed fluorescence depends strongly on the pH; the origin of this effect remains unclear.

Calorimetry↗

PubMed1977

515 nm Absorption changes in Chlorella at short times (4--100 mus) after a flash.

Using Chlorella, three types of absorption changes at 515 nm have been studied in the 4-100 mus time range following a flash. (1) The absorption change observed when both photoreactions are blocked, probably due to the formation of the triplet state of a carotenoid, is show to depend on Photosystem II excitation only. (2) The absorption increase induced by photoreaction I is biphasic; first phase, complete in less than 4 mus, followed by a slower phase with a half-rise time of 15-20 mus. (3) On the other hand, photoreaction II induces only a fast absorption increase (lessthan 4 mus). The time course of the biphasic 515 nm absorption increase induced by photoreaction I is similar to the biphasic absorption decrease previously observed at 480 nm by Cox and Delosme (1976, C.R. Acad. Sci. Paris 282D, 775-778). No significant absorption change is observed at 490 nm. These results suggest that the transmembrane electric field induced by photoreaction I rises to its maximum value in at least two phases within 100 mus following flash excitation.

Chlorella↗