Glycolaldehyde inhibition of CO2transport in the cyanobacteriumSynechococcusUTEX 625

1998 ◽  
Vol 76 (1) ◽  
pp. 1-11
Author(s):  
Christophe Salon ◽  
Qinglin Li ◽  
David Thomas Canvin
Keyword(s):  
Steady State ◽  
Carbonic Anhydrase ◽  
Cell Suspension ◽  
Time Course ◽  
Initial Period ◽  
Cyanobacterial Cell ◽  
Extracellular Medium ◽  
Blue Green Algae ◽  
Carbon Dioxide Uptake ◽  
Concentrating Mechanism

In studies of the inorganic carbon (Ci) concentrating mechanism of cyanobacteria glycolaldehyde is often used to inhibit photosynthetic CO2fixation. As a partial inhibition of active CO2transport by glycolaldehyde under steady-state Ciflux conditions has been recently suggested, in this paper, using mass spectrometry, we investigate in detail the relationship between glycolaldehyde concentration ([GLY]) and CO2transport both during the initial period following illumination of a cyanobacterial cell suspension and during the so-called steady state when an internal Cipool has been allowed to develop. Carbon dioxide uptake following illumination of a cyanobacterial cell suspension was progressively reduced by increasing [GLY] in the medium, both in the absence or in the presence of carbonic anhydrase. The same features were found when either Ciin the form of bicarbonate was injected to a pre-illuminated cell suspension in the presence of carbonic anhydrase in the medium or a pulse of CO2was provided to the cells in the light without carbonic anhydrase in the extracellular medium. Although photosynthesis was completely abolished with 10 mM glycolaldehyde, CO2uptake was only inhibited 20% but was decreased further by higher [GLY]. Double reciprocal plots of CO2uptake versus initial [CO2] determined with a range of [GLY] showed the inhibition to be noncompetitive. To simultaneously study CO2uptake and CO2efflux, H13C18O3was used with cells in which CO2transport alone, or both CO2and HCO3-transport system were allowed to proceed. Cells were inhibited with either iodoacetamide or glycolaldehyde and the time course of the various CO2species in the medium demonstrated that CO2uptake was inhibited partially with glycolaldehyde resulting in a greater CO2efflux from the cells. When the cell suspension was again illuminated, in the presence of glycolaldehyde, initial CO2uptake was greatly reduced, and the extracellular [CO2] eventually rose to a level higher than that which would be expected to be in equilibrium with the amount of Cipresent in the medium. Results are discussed in terms of glycolaldehyde use in Citransport mechanism studies in cyanobacteria. Key words: Synechococcus UTEX 625, blue-green algae, cyanobacteria, CO2transport, HCO3-transport, CO2efflux, inhibitor, Ciconcentrating mechanism.

HCO3− efflux and the regulation of the intracellular Ci pool size in Synechococcus UTEX 625

1997 ◽  
Vol 75 (2) ◽  
pp. 290-300 ◽  
Author(s):  
Christophe Salon ◽  
David Thomas Canvin
Keyword(s):  
Steady State ◽  
Permeability Coefficient ◽  
Silicone Oil ◽  
Cell Envelope ◽  
Initial Period ◽  
Transport Rate ◽  
Cell Permeability ◽  
Blue Green Algae ◽  
The Difference ◽  
Oil Filtration

Cyanobacterial cells of Synechococcus UTEX 625 were suspended in increasing extracellular inorganic carbon (Ci, up to 1 mM) under steady state photosynthesis conditions in a cuvette connected to a mass spectrometer. Photosynthetic CO2 fixation, net CO2, and net HCO3− transport increased with increased extracellular Ci up to 100 μM [C1], with HCO3− transport contributing the most to the maintenance of the internal Ci pool. When the extracellular [Ci] was increased above 100 μM, CO2, fixation and net CO2 transport increased toward their maximum rates but net HCO3− transport progressively declined. At an extracellular [Ci] of 1 mM, the net HCO3− transport rate was only 15% of its value at 100 μM extracellular [Ci]. Under steady state photosynthesis conditions, the gross HCO3− transport rate remained at its maximum value at extracellular [Ci] above 100 μM either when CO2 transport was precluded (i.e., in the presence of 200 μM Na2S) or when HCO3− transport was measured with H14CO3− and silicone oil filtration. As HCO3− efflux, calculated using the permeability coefficient determined at low [Ci], could not account fully for the decrease of the net HCO3− transport rate, Ci efflux and CO2, efflux were measured at high extracellular [Ci] during the initial period of darkness. With increasing intracellular [Ci] Ci efflux over intracellular [Ci] increased linearly but CO2, efflux over intracellular [Ci] was constant, hence the HCO3− efflux obtained by the difference between the Ci and the CO2 efflux increased hyperbolically. Using HCO3− and CO2, efflux, we calculated that the permeability coefficient of the cell envelope for HCO3− but not for CO2 increased with increasing intracellular [Ci]. When the HCO3− efflux was measured under steady state Ci flux conditions in the light, the permeability coefficient of the cell envelope for HCO3− also increased with increasing intracellular [Ci]. Reasons for the change in whole cell permeability to HCO3− at high extracellular [Ci] are discussed. Key words: Synechococcus UTEX 625, blue green algae, cyanobacteria, active HCO3− transport, HCO3− leakage, Ci concentrating mechanism.

Simulation of C1 fluxes in cyanobacteria: comparison between the carboxysome hypothesis and the equilibrium proposal

1997 ◽  
Vol 75 (12) ◽  
pp. 2117-2130 ◽  
Author(s):  
Christophe Salon ◽  
David Thomas Canvin
Keyword(s):  
Mathematical Model ◽  
Steady State ◽  
Kinetic Constants ◽  
Experimental Conditions ◽  
Extracellular Medium ◽  
Blue Green Algae ◽  
Permeability Coefficients ◽  
Inorganic Species ◽  
Wide Range ◽  
Entire Cell

Inorganic carbon fluxes were simulated by a mathematical model using an equilibrium hypothesis for a wide range of conditions in a closed system composed of air-grown cells of Synechococcus UTEX 625 in a reaction vessel connected to a mass spectrometer. The metabolic scheme took into account the input fluxes of CO2 and HCO3− transport into the cells, the output fluxes of CO2 and HCO3− efflux, the diversion of Q toward the formation of the internal C2 pool, and photosynthetic CO2 fixation. The equations expressed the variation in concentration of each inorganic species outside and inside the cell as a function of time. The input fluxes were previously characterized by their kinetic constants (K1/2 and Vm) both during initial uptake occurring upon illumination of the cells and under steady-state photosynthesis conditions. The efflux rates of the various Ci species from the cells were investigated under a wide variety of experimental conditions. Using these efflux rates, the permeability coefficients of the cell for CO2 and HCO3− were calculated previously. Using the kinetic constants for CO2 and HCO3− transport, the permeability coefficients of the cell for CO2 and HCO3− and the geometrical characteristics of the cells, the model simulated precisely the [HCO3−]/[CO2] ratio and the [CO2] and [O2] changes in the extracellular medium as well as the rate of filling of the internal Ci pool under various conditions. Accurate fitting of experimental data with calculated values were possible only when the intracellular Ci species were assumed to be in equilibrium throughout the entire cell volume. Results are discussed and compared with those given by previous hypotheses. Key words: Synechococcus UTEX 625, blue green algae, cyanobacteria, mathematical model, active CO2 transport, active HCO3− transport, steady state, photosynthesis, Ci concentrating mechanism.

Reduction in postsynaptic inhibition during maintained electrical stimulation of different nerves in the cat hindlimb

1994 ◽  
Vol 71 (6) ◽  
pp. 2281-2293 ◽  
Author(s):  
C. J. Heckman ◽  
J. F. Miller ◽  
M. Munson ◽  
K. D. Paul ◽  
W. Z. Rymer
Keyword(s):  
Electrical Stimulation ◽  
Steady State ◽  
Time Course ◽  
Initial Period ◽  
Input Resistance ◽  
Medial Gastrocnemius ◽  
Rapid Phase ◽  
Afferent Pathways ◽  
Lateral Gastrocnemius ◽  
Stimulation Of

1. Steady-state postsynaptic potentials (PSPs) were generated by prolonged (approximately 1 s) high-frequency (100-200 Hz) electrical stimulation of nerves in the cat hindlimb. The characteristics of these steady-state PSPs were compared for two polysynaptic afferent pathways (ipsilateral cutaneous sural vs. contralateral peroneal nerves), two animal preparations (decerebrate vs. chloralose), and two motoneuron pools (medial gastrocnemius vs. lateral gastrocnemius-soleus). 2. PSPs from both nerves usually (36 of 51 cases) contained a mixture of depolarizing and hyperpolarizing components. In all 36 cases where the PSP contained a hyperpolarizing component, a consistent qualitative pattern emerged during prolonged stimulation: the hyperpolarization reached a peak approximately 20 ms after stimulation onset and then decayed with a biphasic time course that consisted of an initial rapid phase (20–40 ms) and a later slower phase (200–400 ms) before the steady-state value was reached. This pattern occurred regardless of the differences in polysynaptic afferent pathways, animal preparations, and motoneuron pools. 3. The consistency of this overall pattern was remarkable, given the existence of several quantitative differences among the PSPs. These differences include the following: hyperpolarizing components were least common in the sural and peroneal PSPs in the decerebrate preparation. And only these sural and peroneal PSPs tended to have prolonged afterpotentials after stimulus cessation. The steady-state sural PSPs in the decerebrate preparation tended to generate the largest PSPs and, moreover, these PSPs did not follow the overall trend of having a statistically significant relation between the amplitude of the initial hyperpolarization and the amount of its decay. Finally, transient sural PSPs in lateral gastrocnemius-soleus motoneurons in the decerebrate preparation tended to have the largest hyperpolarizations. 4. To determine whether the decay of the hyperpolarization and the subsequent dominance of depolarization was due to a decreased inhibition or an increased excitation, injected current pulses were utilized to measure the changes in the cell's input resistance during the course of the synaptic input. A strong decrease in input resistance accompanied the initial period of maximal hyperpolarization (50% with respect to the resting input resistance). Input resistance then returned toward resting values as hyperpolarization faded and depolarization became dominant. However, there remained a persistent decrease in input resistance during the final phase of the PSP that amounted to < 10% of the initial decrease. These findings indicated that much of the reduction in hyperpolarization reflected a progressive decrease in synaptic efficacy for the inhibition.(ABSTRACT TRUNCATED AT 400 WORDS)

Separation of carotid body chemoreceptor responses to O2 and CO2 by oligomycin and by antimycin A

1982 ◽  
Vol 242 (3) ◽  
pp. C200-C206 ◽  
Author(s):  
E. Mulligan ◽  
S. Lahiri
Keyword(s):  
Steady State ◽  
Carbonic Anhydrase ◽  
Partial Pressure ◽  
Carotid Body ◽  
Body Tissue ◽  
Antimycin A ◽  
Tissue Ph ◽  
Co2 Partial Pressure ◽  
O2 Partial Pressure ◽  
Metabolic Hypothesis

The cat carotid chemoreceptor O2 and CO2 responses can be separated by oligomycin and by antimycin A. Both of these agents greatly diminish or abolish the chemoreceptor O2 response but not the nicotine or CO2 responses. After either oligomycin or antimycin, the responses to increases and decreases in arterial CO2 partial pressure (PaCO2) consisted of increases and decreases in activity characterized respectively by exaggerated overshoots and undershoots. These were eliminated by the carbonic anhydrase inhibitor, acetazolamide, suggesting that they resulted from changes in carotid body tissue pH. The steady-state PaCO2 response remaining after oligomycin was no longer dependent on arterial O2 partial pressure (PaO2). All effects of antimycin were readily reversible in about 20 min. The separation of the responses to O2 and CO2 indicates that there may be at least partially separate pathways of chemoreception for these two stimuli. The similarity of the oligomycin and antimycin results supports the metabolic hypothesis of chemoreception.

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 The Dependence of the Oxygen-Concentrating Mechanism of the Teleost Eye (Salmo gairdneri) on the Enzyme Carbonic Anhydrase

1969 ◽  
Vol 54 (2) ◽  
pp. 203-211 ◽  
Author(s):  
Michael B. Fairbanks ◽  
J. Russell Hoffert ◽  
Paul O. Fromm
Keyword(s):  
Carbonic Anhydrase ◽  
Environmental Water ◽  
Salmo Gairdneri ◽  
Complete Suppression ◽  
Oxygen Inhibition ◽  
Rete Mirabile ◽  
Arterial Blood ◽  
Concentrating Mechanism ◽  
The One ◽  
Erythrocyte Carbonic Anhydrase

Microoxygen polarographic electrodes were constructed and used to measure oxygen tension (POO2) in the eyes of rainbow trout (Salmo gairdneri). The values obtained are compared with arterial blood and environmental water POO2 and indicate that there is an oxygen-concentrating mechanism in the eye supplying oxygen to the avascular retina. Anatomically similar retes suggest that the mechanism is similar to the one which exists in the swim bladder. Elimination of the arterial blood supply to the choroidal gland rete mirabile of the eye (through pseudobranchectomy) and the consequent lowering of ocular oxygen tensions implicate the choroidal gland as one of the major components of the oxygen-concentrating mechanism. After pseudobranchectomy the presence of ocular POO2 above that of arterial blood is indicative of a secondary structure in the eye capable of concentrating oxygen. Inhibition of carbonic anhydrase, using acetazolamide, is shown to result in complete suppression of the oxygen-concentrating mechanism. A hypothesis is advanced for the participation of retinal-choroidal and erythrocyte carbonic anhydrase in the oxygen-concentrating mechanism.

Differential patterns of transcript accumulation during human myogenesis

1987 ◽  
Vol 7 (11) ◽  
pp. 4100-4114
Author(s):  
P Gunning ◽  
E Hardeman ◽  
R Wade ◽  
P Ponte ◽  
W Bains ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Carbonic Anhydrase ◽  
Myosin Heavy Chain ◽  
Heavy Chain ◽  
Time Course ◽  
Human Skeletal Muscle ◽  
Transcript Accumulation ◽  
Mrna Accumulation ◽  
Adult Human ◽  
Alpha Actin

We evaluated the extent to which muscle-specific genes display identical patterns of mRNA accumulation during human myogenesis. Cloned satellite cells isolated from adult human skeletal muscle were expanded in culture, and RNA was isolated from low- and high-confluence cells and from fusing cultures over a 15-day time course. The accumulation of over 20 different transcripts was compared in these samples with that in fetal and adult human skeletal muscle. The expression of carbonic anhydrase 3, myoglobin, HSP83, and mRNAs encoding eight unknown proteins were examined in human myogenic cultures. In general, the expression of most of the mRNAs was induced after fusion to form myotubes. However, several exceptions, including carbonic anhydrase and myoglobin, showed no detectable expression in early myotubes. Comparison of all transcripts demonstrated little, if any, identity of mRNA accumulation patterns. Similar variability was also seen for mRNAs which were also expressed in nonmuscle cells. Accumulation of mRNAs encoding alpha-skeletal, alpha-cardiac, beta- and gamma-actin, total myosin heavy chain, and alpha- and beta-tubulin also displayed discordant regulation, which has important implications for sarcomere assembly. Cardiac actin was the only muscle-specific transcript that was detected in low-confluency cells and was the major alpha-actin mRNA at all times in fusing cultures. Skeletal actin was transiently induced in fusing cultures and then reduced by an order of magnitude. Total myosin heavy-chain mRNA accumulation lagged behind that of alpha-actin. Whereas beta- and gamma-actin displayed a sharp decrease after initiation of fusion and thereafter did not change, alpha- and beta-tubulin were transiently induced to a high level during the time course in culture. We conclude that each gene may have its own unique determinants of transcript accumulation and that the phenotype of a muscle may not be determined so much by which genes are active or silent but rather by the extent to which their transcript levels are modulated. Finally, we observed that patterns of transcript accumulation established within the myotube cultures were consistent with the hypothesis that myoblasts isolated from adult tissue recapitulate a myogenic developmental program. However, we also detected a transient appearance of adult skeletal muscle-specific transcripts in high-confluence myoblast cultures. This indicates that the initial differentiation of these myoblasts may reflect a more complex process than simple recapitulation of development.

Time course of exchanges between red cells and extracellular fluid during CO2 uptake

1975 ◽  
Vol 38 (4) ◽  
pp. 710-718 ◽  
Author(s):  
R. E. Forster ◽  
E. D. Crandall
Keyword(s):  
Carbonic Anhydrase ◽  
Time Course ◽  
Extracellular Fluid ◽  
Extracellular Ph ◽  
Co2 Uptake ◽  
Sudden Increase ◽  
Red Cell ◽  
Ph Change ◽  
Red Cell Membrane

A stopped-flow rapid-reaction apparatus was used to follow the time course of extracellular pH in a human red cell suspension following a sudden increase in PCO2. The extracellular pH change was slow (t1/2 similar to 3.5 s) considering the presence of carbonic anhydrase in the cells. When carbonic anhydrase was added to the extracellular fluid, the half-time was reduced to less than 20 ms. The explanation for these phenomena is that the equilibration of H+ across the red cell membrane is rate-limited by the uncatalyzed reaction CO2 plus H2O formed from H2CO3 outside the cells. A theoretical model was developed which successfully reproduced the experimental results. When the model was used to simulate CO2 exchange in vivo, it was determined that blood PCO2 and pH require long times (greater than 50 s) to approach equilibrium between cells and plasma after leaving an exchange capillary. We conclude that cell-plasma equilibrium may never be reached in vivo, and that in vitro measurements of these quantities may not represent their true values at the site of sampling.

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.

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