scholarly journals TIME COURSE AND QUANTUM EFFICIENCY OF PHOTOSYNTHESIS IN CHLORELLA

1953 ◽  
Vol 36 (4) ◽  
pp. 563-579 ◽  
Author(s):  
Frederick S. Brackett ◽  
Rodney A. Olson ◽  
Robert G. Crickard
Keyword(s):  
Steady State ◽  
Quantum Yield ◽  
Dark Adaptation ◽  
Time Course ◽  
Random Distribution ◽  
Initial Rate ◽  
Chlorophyll Concentration ◽  
Intermittent Light ◽  
Quantum Requirement ◽  
Different Cultures

1. Though the quantum yield remains constant for different samples of the same culture despite great changes in respiration due to dark adaptation, the quantum requirement for different cultures varies from 6.1 to 13.5 quanta per molecule of oxygen evolved (q/m). 2. This variation from one culture to another appears to depend upon chlorophyll concentration, though other paralleling factors cannot be ruled out. 3. Both chlorophyll concentration and quantum requirement show a random distribution. A statistical median for 50 cultures and 99 determinations gives q/m = 8.5 with a systematic uncertainty of perhaps 10 per cent. Since the variations are real, the median is regarded as less important than the lower limit approached (about q/m = 6). 4. Dark adaptation under aerobic conditions produces an initial photosynthetic rate of nearly zero. The immediate rise to steady state is somewhat logarithmic in character and may require over 3 minutes. 5. In intermittent light (of periods from 1 to 6 minutes) the induction observed in subsequent light periods starts from a finite initial rate and occupies a shorter time, often as little as 30 seconds. 6. The theoretical importance of aerobic induction is discussed. A chlorophyll cycle of two photochemical steps is found to satisfy most of the observed characteristics and to be compatible with an efficiency independent of intensity.

Abstract 5385: Transport of Free Fatty Acids in Cardiac Myocytes is Mediated by a Plasma Membrane Pump as Revealed by Monitoring Cytoplasmic Unbound Free Fatty Acids

Circulation ◽  
2008 ◽  
Vol 118 (suppl_18) ◽  
Author(s):  
Andrew N Carley ◽  
J P Kampf ◽  
Alan M Kleinfeld
Keyword(s):  
Fatty Acids ◽  
Plasma Membrane ◽  
Steady State ◽  
Free Fatty Acids ◽  
Cardiac Myocytes ◽  
Time Course ◽  
Plasma Membranes ◽  
Initial Rate ◽  
Ffa Metabolism ◽  
Ffa Transport

The transport of FFA across the plasma membrane represents one of the earliest points at which FFA metabolism can be controlled by cardiac myocytes. Using novel methods to measure the intracellular unbound concentration of FFA ([FFA i ]), the first direct measurements of FFA transport across cardiac plasma membranes have been performed in freshly isolated cardiac myoctyes. Measurements of the unbound concentrations of FFA (FFA u ) in the aqueous phase were performed using the fluorescent ratio probe ADIFAB. Cardiac myocytes were microinjected with ADIFAB, and the transport of oleate and palmitate was determined by monitoring [FFA i ] using fluorescence ratio microscopy. FFA influx was initiated by rapidly increasing the extracellular concentration of FFA u ([FFA o ]) using FFA-BSA complexes, which clamped [FFA o ] at fixed values. The time course of influx was monitored from the change in [FFA i ], which rose exponentially to a steady state level (k influx ~ 0.01 s −1 ). Once steady state was achieved, efflux was initiated by changing the extracellular media back to zero [FFA o ]. Efflux was monitored by the decrease in [FFA i ] which, like influx, revealed exponential behavior (k efflux ~ 0.02 s −1 ). At steady state [FFA i ] was greater than [FFA o ] by a factor of ~3.5, indicating that during influx FFA are pumped up a concentration gradient. Both the initial rate of transport and the gradient ([FFA i ] > [FFA o ]) revealed saturation with increasing [FFA o ]. The initial rate of influx saturated at [FFA o ] > 200 nM, while the [FFA i ] > [FFA o ] gradient was relatively constant (~ 3.5) but began to decrease and approached 1 at [FFA o ] > 200 nM. The efflux rate constant decreased for [FFA o ] > zero, suggesting that efflux may be regulated by a mechanism that senses the level of circulating FFA u . Our results indicate that the mechanism of FFA transport across cardiac myocytes is regulated by the plasma membrane and allows for the efficient storage and release of FFA from cardiac myocytes. We suggest that this mechanism involves an as yet unknown membrane protein pump which enables the cells to accumulate surprisingly high concentrations of FFA. The ability to measure [FFA i ] and the demonstration of efflux are significant steps in understanding cardiac FFA metabolism. This research has received full or partial funding support from the American Heart Association, AHA Western States Affiliate (California, Nevada & Utah).

scholarly journals A steady-state mechanism can account for the properties of inositol 2,4,5-trisphosphate-stimulated Ca2+ release from permeabilized L1210 cells

1993 ◽  
Vol 289 (3) ◽  
pp. 861-866 ◽  
Author(s):  
J W Loomis-Husselbee ◽  
A P Dawson
Keyword(s):  
Steady State ◽  
Small Proportion ◽  
Time Course ◽  
Initial Rate ◽  
Atpase Inhibitor ◽  
Efflux Rate ◽  
Rapid Phase ◽  
L1210 Cells ◽  
Low Concentrations ◽  
Stimulation Of

We have investigated the effects of sub-maximal Ins(2,4,5)P3 concentrations on the Ca2+ permeability of the residual undischarged Ca2+ stores in electroporated or digitonin-permeabilized L1210 cells by measuring Ca(2+)-efflux rate after addition of the ATPase inhibitor thapsigargin. Low concentrations of Ins(2,4,5)P3, causing rapid discharge of a small proportion of the releasable Ca2+, result in a substantial stimulation of Ca2+ efflux after thapsigargin addition. This indicates firstly that in the absence of thapsigargin there must have been a substantial, counterbalancing, increase in rate of Ca2+ pumping, and secondly that the increased Ca2+ permeability is more consistent with a steady state than with a quantal model of Ca2+ release. Similar increases in passive Ca2+ permeability are produced by addition of concentrations of ionomycin which produce equivalent changes in Ca2+ loading to those produced by Ins(2,4,5)P3, although the time course and initial rate of Ca2+ release are very much slower. In the presence of a Ca(2+)-buffering system, the time course of Ca2+ release by Ins(2,4,5)P3 becomes superimposable on that of ionomycin, indicating that the initial rapid phase of Ins(2,4,5)P3-stimulated Ca2+ is at least partially due to positive feedback from extravesicular Ca2+.

Inward rectification in rat nucleus accumbens neurons

1989 ◽  
Vol 62 (6) ◽  
pp. 1280-1286 ◽  
Author(s):  
N. Uchimura ◽  
E. Cherubini ◽  
R. A. North
Keyword(s):  
Steady State ◽  
Nucleus Accumbens ◽  
Time Course ◽  
Potassium Conductance ◽  
Resting Potential ◽  
Inward Rectification ◽  
Resting Membrane Potential ◽  
Potential Range ◽  
Inward Current ◽  
Rat Nucleus Accumbens

1. Intracellular recordings were made from neurons in slices cut from the rat nucleus accumbens septi. Membrane currents were measured with a single-electrode voltage-clamp amplifier in the potential range -50 to -140 mV. 2. In control conditions (2.5 mM potassium), the resting membrane potential of the neurons was -83.4 +/- 1.1 (SE) mV (n = 157). Steady state membrane conductance was voltage dependent, being 34.8 +/- 1.7 nS (n = 25) at -100 mV and 8.0 +/- 0.7 nS (n = 25) at -60 mV. 3. Barium (1 microM) markedly reduced the inward rectification and caused a small inward current (40.6 +/- 8.7 pA, n = 8) at the resting potential. These effects became larger with higher barium concentrations, and, in 100 microM barium, the current-voltage relation was straight. 4. The block of the inward current by barium (at -130 mV) occurred with an exponential time course; the time constant was approximately 1 s at 1 microM barium and less than 90 ms with 100 microM. Strontium had effects similar to those of barium, but 1000-fold higher concentrations were required. Cesium chloride (2 mM) and rubidium chloride (2 mM) also blocked the inward rectification; their action reached steady state within 50 ms. 5. It is concluded that the nucleus accumbens neurons have a potassium conductance with many features of a typical inward rectifier and that this contributes to the potassium conductance at the resting potential.

scholarly journals Studies on glycogen synthesis in pigeon liver homogenates. Glycogen synthesis from glucose monophosphates and uridine diphosphate glucose

1967 ◽  
Vol 105 (2) ◽  
pp. 515-519 ◽  
Author(s):  
V. N. Nigam
Keyword(s):  
Time Course ◽  
Initial Rate ◽  
Glycogen Synthesis ◽  
Uridine Diphosphate ◽  
Cytoplasmic Fraction ◽  
Uridine Diphosphate Glucose ◽  
Diphosphate Glucose ◽  
Liver Homogenates ◽  
Pigeon Liver ◽  
Glycogen Formation

Comparative time-course studies of glycogen synthesis from glucose 6-phosphate, glucose 1-phosphate and UDP-glucose show that glucose 1-phosphate forms glycogen at an initial rate faster than that obtained with glucose 6-phosphate and UDP-glucose. After 5min. the rates from glucose monophosphates are considerably slower. 2,4-Dinitrophenol decreases glycogen synthesis from both glucose monophosphates, whereas arsenate and EDTA increase glycogen synthesis from glucose 1-phosphate and inhibit the reaction from glucose 6-phosphate, galactose and galactose 1-phosphate. Mitochondria-free pigeon liver cytoplasmic fraction forms less glycogen from glucose monophosphates than does the whole homogenate. 2-Deoxyglucose 6-phosphate inhibits glycogen synthesis from glucose monophosphates. Glycogen formation from UDP-glucose is relatively unaffected by dinitrophenol, by arsenate, by EDTA, by 2-deoxyglucose 6-phosphate and by the removal of mitochondria from the whole homogenate.

Faster adjustment of O2 uptake to the energy requirement of exercise in the trained state

1978 ◽  
Vol 44 (6) ◽  
pp. 877-881 ◽  
Author(s):  
R. C. Hickson ◽  
H. A. Bomze ◽  
J. O. Hollozy
Keyword(s):  
Steady State ◽  
Exercise Training ◽  
Training Program ◽  
Endurance Exercise ◽  
Time Course ◽  
Energy Requirement ◽  
Constant Load ◽  
O2 Uptake ◽  
Endurance Exercise Training

The purpose of this study was to determine the effect of endurance exercise training on the time course of the increase in VO2 toward steady state in response to submaximal constant load work. Seven men participated in a strenuous program of endurance exercise for 40 min/day, 6 days/wk for 10 wk. Their average VO2max increased from 3.29 liters before training to 4.53 liters at the end of the training program. VO2 was measured continuously on a breath-by-breath basis at work rates requiring 40%, 50%, 60%, or 70% of VO2max before training. After training the subjects were retested both at the same absolute and the same relative work rates. The increases in VO2 toward steady state occurred more rapidly in the trained than in the untrained state both at the same absolute and at the same relative work rates. The finding that O2 uptake rises to meet O2 demand more rapidly in the trained than in the untrained state provides evidence that the working muscles become less hypoxic at the onset of exercise of the same intensity after training.

Estimation of the rate of appearance in the non-steady state with a two-compartment model

1992 ◽  
Vol 263 (2) ◽  
pp. E400-E415 ◽  
Author(s):  
A. Mari
Keyword(s):  
Steady State ◽  
Time Course ◽  
Specific Activity ◽  
Glucose Production ◽  
Compartment Model ◽  
New Method ◽  
Two Compartment Model ◽  
Glucose Clamp Technique ◽  
Glucose Output ◽  
The Relationship

A simple tracer-based method for calculating the rate of appearance of endogenous substances in the non-steady state, free from the inconsistencies of Steele's equation, is still lacking. This paper presents a method based on a two-compartment model by which the rate of appearance can be calculated with only a modest increase in complexity over Steele's approach. An equation is developed where the rate of appearance is expressed as a sum of three terms: a steady-state term, a term for the first compartment, and a term for the second compartment. The formula employs three parameters and makes the relationship between rate of appearance and specific activity changes explicit. An equation is also provided for estimating the error of the method in each individual run. The algorithm can be implemented with a spreadsheet on a personal computer. Simulated and experimental data obtained by the hyperinsulinemic euglycemic glucose clamp technique were used as a test. The accuracy with which the time course of glucose production could be reconstructed was clearly better than that using Steele's equation. Marked negative values for endogenous glucose output were calculated with Steele's equation but not with the new method. The characteristics of generality, simplicity, and accuracy and the availability of an error estimate make this new method suitable for routine application to non-steady-state tracer analysis.

Spike frequency adaptation studied in hypoglossal motoneurons of the rat

1995 ◽  
Vol 73 (5) ◽  
pp. 1799-1810 ◽  
Author(s):  
A. Sawczuk ◽  
R. K. Powers ◽  
M. D. Binder
Keyword(s):  
Steady State ◽  
Time Course ◽  
Firing Frequency ◽  
Spike Frequency ◽  
Membrane Properties ◽  
Repetitive Firing ◽  
Hypoglossal Nucleus ◽  
Spike Frequency Adaptation ◽  
Frequency Adaptation ◽  
Three Phases

1. We studied spike frequency adaptation of motoneuron discharge in the rat hypoglossal nucleus using a brain stem slice preparation. The characteristics of adaptation in response to long (60 s) injected current steps were qualitatively similar to those observed previously in cat hindlimb motoneurons. The discharge rate typically exhibited a rapid initial decline, characterized by a linear frequency-time relation, followed by a gradual exponential decline that continued for the duration of current injection. However, a more systematic, quantitative analysis of the data revealed that there were often three distinct phases of the adaptation rather than two. 2. The three phases of adaptation (initial, early, and late) were present in at least one 60-s trial of repetitive firing in all but a small number of motoneurons. Initial adaptation was limited to the first few spikes except in a few trials (7%) in which there was no initial adaptation. The time course of the subsequent decline in rate could be adequately described by a single-exponential function in about half of the trials (48%). In the remaining trials this subsequent decline in frequency was better described as the sum of two exponential functions: an early phase, lasting < 2 s, and a late phase, which lasted for the duration of the discharge period. 3. The magnitude of initial adaptation was correlated with the initial firing frequency (i.e., the reciprocal of the 1st interspike interval). The magnitudes of the early and late phases of adaptation were correlated with the firing frequency reached at the end of initial adaptation. Neither the magnitudes nor the time courses of the three phases were correlated with other membrane properties such as input resistance, rheobase, or repetitive firing threshold. 4. The slope of the frequency-current (f-I) curve was steeper in the initial phase (first 2-5 spikes) than in either the early (< 2 s) or late (> 2 s) phases of adaptation as previously reported by other investigators. In the absence of early adaptation, a steady state for the f-I slope was reached by 0.7-1 s, the time typically reported in studies of repetitive discharge. However, when early adaptation was present (50% of the trials), a steady-state value for the f-I slope was not reached until the cell had discharged for > 1 s. 5. To characterize the time course of firing rate recovery from the adaptive processes, the current was turned off for periods of < or = 10 s during the course of a 60-s trial.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals Distinct neural sources underlying visual word form processing as revealed by steady state visual evoked potentials (SSVEP)

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Fang Wang ◽  
Blair Kaneshiro ◽  
C. Benjamin Strauber ◽  
Lindsey Hasak ◽  
Quynh Trang H. Nguyen ◽  
...  
Keyword(s):  
Steady State ◽  
Word Recognition ◽  
Visual Word Recognition ◽  
Time Course ◽  
Signal To Noise Ratio ◽  
Visual Word ◽  
High Signal ◽  
Hierarchical Processing ◽  
Form Processing ◽  
Visual Evoked

AbstractEEG has been central to investigations of the time course of various neural functions underpinning visual word recognition. Recently the steady-state visual evoked potential (SSVEP) paradigm has been increasingly adopted for word recognition studies due to its high signal-to-noise ratio. Such studies, however, have been typically framed around a single source in the left ventral occipitotemporal cortex (vOT). Here, we combine SSVEP recorded from 16 adult native English speakers with a data-driven spatial filtering approach—Reliable Components Analysis (RCA)—to elucidate distinct functional sources with overlapping yet separable time courses and topographies that emerge when contrasting words with pseudofont visual controls. The first component topography was maximal over left vOT regions with a shorter latency (approximately 180 ms). A second component was maximal over more dorsal parietal regions with a longer latency (approximately 260 ms). Both components consistently emerged across a range of parameter manipulations including changes in the spatial overlap between successive stimuli, and changes in both base and deviation frequency. We then contrasted word-in-nonword and word-in-pseudoword to test the hierarchical processing mechanisms underlying visual word recognition. Results suggest that these hierarchical contrasts fail to evoke a unitary component that might be reasonably associated with lexical access.

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