Total Pool Size Research Articles

Seasonal differences in xanthophyll cycle characteristics and antioxidants in Mahonia repens growing in different light environments.

We investigated differences between summer and winter in photosynthesis, xanthophyll cycle-dependent energy dissipation, and antioxidant systems in populations of Mahonia repens (Lindley) Don growing in the eastern foothills of the Colorado Rocky Mountains in deep shade, full exposure, and under a single-layered canopy of Pinus ponderosa (partially shaded). In summer, increasing growth irradiance (from deep shade to partial shade to full exposure) was associated with increased xanthophyll cycle-dependent energy dissipation in PSII and an increased capacity to detoxify reactive reduced oxygen species, as measured by increases in the activities of ascorbate peroxidase, superoxide scavenging, glutathione reductase, and monodehydroascorbate reductase, as well as increases in leaf ascorbate and glutathione content. Leaves of exposed and partially shaded plants exhibited decreased capacities for photosynthetic O2 evolution in winter compared to summer, while in the deeply shaded plants this parameter did not differ seasonally. Seasonal differences in the levels of antioxidants generally exhibited an inverse response to photosynthesis, being higher in winter compared to summer in the exposed and partially shaded populations, but remaining unchanged in the deeply shaded population. In addition, total pool size and conversion state of the xanthophyll cycle were higher in winter than in summer in all populations. These trends suggest that both xanthophyll cycle-dependent energy dissipation in PSII and the capacity to detoxify reactive reduced oxygen species responded to the level of excess light absorption.

Regulation of Synaptic Vesicle Recycling by Calcium and Serotonin

Serotonin, a neuromodulator at the crayfish neuromuscular junction, regulates neurotransmission without changing intracellular calcium levels. However, the mechanism of this regulation remains unclear. By analysis of synaptic depression using a depletion model and measurement of vesicle recycling using the styryl dye FM1-43, we show that serotonin increases the number of vesicles available for transmitter release (total synaptic vesicle pool size). This regulation is due either to an increase in the number of vesicles at each release site or to an activation of previously nonsecreting or silent synapses. We also observed that low calcium medium rendered part of the vesicle pool unavailable for release. These results suggest a new mechanism for regulating synaptic transmission.

Pathogen-induced changes in the antioxidant status of the apoplast in barley leaves

Leaves of two barley (Hordeum vulgare L.) isolines, Alg-R, which has the dominant Mla1 allele conferring hypersensitive race-specific resistance to avirulent races of Blumeria graminis, and Alg-S, which has the recessive mla1 allele for susceptibility to attack, were inoculated with B. graminis f. sp. hordei. Total leaf and apoplastic antioxidants were measured 24 h after inoculation when maximum numbers of attacked cells showed hypersensitive death in Alg-R. Cytoplasmic contamination of the apoplastic extracts, judged by the marker enzyme glucose-6-phosphate dehydrogenase, was very low (less than 2%) even in inoculated plants. Dehydroascorbate, glutathione, superoxide dismutase, catalase, ascorbate peroxidase, glutathione reductase, monodehydroascorbate reductase, and dehydroascorbate reductase were present in the apoplast. Inoculation had no effect on the total foliar ascorbate pool size or the redox state. The glutathione content of Alg-S leaves and apoplast decreased, whereas that of Alg-R leaves and apoplast increased after pathogen attack, but the redox state was unchanged in both cases. Large increases in foliar catalase activity were observed in Alg-S but not in Alg-R leaves. Pathogen-induced increases in the apoplastic antioxidant enzyme activities were observed. We conclude that sustained oxidation does not occur and that differential strategies of antioxidant response in Alg-S and Alg-R may contribute to pathogen sensitivity.

Effect of allowed grazing time, inert rumen bulk and length of starvation before grazing on the weight, composition and dermentative end‐products of the rumen contents of lactating dairy cows

AbstractThe effect of length of the allowed grazing time (Experiment 1), length of starvation time and placement in the rumen of inert bulk material before grazing (Experiment 2) on liquid and particulate rumen pool sizes, composition and fermentability was investigated. In Experiment 1, four lengths of allowed grazing time (1.00, 1.75, 2.50 and 3.25 h) after overnight starvation were compared. The allowed grazing time had no significant effect on total and liquid rumen pool sizes after grazing but did affect (P < 0.05) dry‐matter (DM) and organic matter (OM) rumen pool sizes. The non‐significant diferences between the volatile fatty acid (VFA) rumen pool sizes before and after 1 h of grazing may indicate a delay in the availability of the more rapidly fermentable substrate for the microorganisms. The total VFA remen pool sizes increased significantly (P < 0.01) with the allowed grazing time, which suggests that these fermentation products may be involved in the control of the grazing time in later stages during the day. Experiment 2 consisted of a factorial combination of two lengths of starvation before grazing (16.5 and 2.5 h) and the presence or absence in the rummen of 12.5 kg of a synthetic indigestible material. The duration of starvation before grazing did not affect significantly the particulate, ammonia and VFA rumen pool sizes after grazing except for propionic acid, which was reduced (P < 0.09) by the longer starvation time. The inclusion of inert bulk material in the rumen before grazing significantly reduced (P < 0.05) the total, Liquid DM, OM, and ammonia rumen pool sizes but not the VFA rumen pool sizes after grazing. High levels of ammonia as well as total rumen contents may be involved in the control of the grazing time in this experiment.

Patterns of induced and constitutive monoterpene production in conifer needles in relation to insect herbivory.

Studies were conducted to determine whether herbivore-induced synthesis of monoterpenes occurs in the needles of ponderosa pine (Pinus ponderosa Lawson), lodgepole pine (P. contorta Douglas var. latifolia Engelmann), white fir (Abies concolor Lindl. and Gordon) and Engelmann spruce [Picea engelmanii (Parry) Engelm.]. In the needles of all species except Engelmann spruce, simulated herbivory significantly induced the activity of monoterpene cyclases 4-8 days after wounding. In ponderosa pine, real herbivory by last-instar tiger moth larvae (Halisdota ingens Hy. Edwards: Lepidoptera) induced a significantly larger response (4.5-fold increase in monoterpene cyclase activity) than did simulated herbivory (2.5-fold increase). To our knowledge, this is the first report of herbivore-induced increases in monoterpene synthesis in needle tissue. Despite this increase in monoterpene synthesis, we observed no significant increase in total monoterpene pool size in wounded needles compared to controls. Large increases in the rate of monoterpene volatilization were observed in response to wounding. We conclude that the volatile losses caused by tissue damage compensate for herbivore-induced monoterpene synthesis, resulting in no change in pool size. Tiger moth larvae consume ponderosa pine needles in a pattern that begins at the tip and proceeds downward to midway along the needle, at which point they move to an undamaged needle. Constitutive monoterpene concentrations and monoterpene cyclase activities were highest in the lower half of ponderosa pine needles. The monoterpene profile also differed between the upper and lower needle halves, the lower half possessing an additional one to four monoterpene forms. We propose that the increasing gradient in monoterpene concentrations and number of monoterpenes along the needle from tip to base deters feeding beyond the midway point and provides time for the induction of increased cyclase activity and production of new monoterpenes. The induction of new monoterpene synthesis may have a role in replacing monoterpenes lost through damage-induced volatilization and preventing extreme compromise of the constitutive defense system.

Endogenous Surfactant Production in Preterm Infants Is Not Supressed By Exogenous Surfactant Administration

Aims. Whether endogenous surfactant production in preterm infants changes due to exogenous surfactant therapy is unknown. Therefore, we measured endogenous surfactant production with a new method using stable isotopes. Methods. Four preterm infants (992±88g, 27.9±0.8 wk) with mild neonatal RDS without exogenous surfactant treatment and 4 preterm infants (968±74 g, 27.6±1.3 wk) with severe RDS with exogenous surfactant treatment were included. All patients received a 24h [U-13C]glucose infusion, starting 4.2±1.1 h after birth. Tracheal aspirates were obtained and the surfactant phosphatidylcholine(PC) was isolated. The enrichment of plasma glucose and of palmitic acid in surfactant PC was measured by GC-IRMS. The fractional synthesis rate (FSR) which is the fraction of the total pool synthesised per day was calculated as the PC palmitate enrichment divided by the steady state plasma glucose enrichment. The absolute production rate was calculated as the FSR times the total pool size. Results. In the untreated patients the surfactant PC pool size is ≤ 87 mg/kg, after 2x surfactant treatment the total surfactant PC pool size is -179 mg/kg.Table

PHOTOSYNTHESIS AND GROWTH OF TWO RAIN FOREST SPECIES IN SIMULATED GAPS UNDER ELEVATED CO2

Two species common to the temperate rain forests of New South Wales, Australia (Doryphora sassafras and Acmena smithii) were grown for 2 wk in either ambient (350 μL/L) or elevated (700 μL/L) CO2 concentrations and low light (30 μmol photons·m−2·s−1) after which the seedlings were exposed for over 9 wk to a midday 2-h high-light period (1250 μmol photons·m−2·s−1, maximum) to simulate a tree fall gap. For both species, plants grown in elevated CO2 had greater biomass than plants grown in ambient CO2. However, relative increases in biomass were greater in Acmena, which is an early-successional species, than Doryphora, which is a late-successional species. Doryphora sassafras also had greater reductions in photosynthetic efficiency, as measured by chlorophyll fluorescence techniques (Fv/Fm) upon exposure to the high-light treatment than Acmena. Recovery in quantum efficiencies over time was observed for Doryphora, implying physiological acclimation to the new light environment. Plants grown in elevated CO2 had lower values of Fv/Fm than plants grown in ambient CO2, but these differences between CO2 treatments were only significant for the late-successional Doryphora. Although exposure to the simulated tree fall gap dramatically increased the conversion of pigments of the xanthophyll cycle, as well as increased the total pool size of xanthophyll cycle pigments relative to total chlorophyll concentration, there were no differences in either parameter between CO2 treatments. Leaves of Doryphora and those seedlings grown in elevated CO2 had greater starch concentrations than Acmena and those seedlings grown in ambient CO2, respectively. The reduction in quantum efficiencies for plants grown in elevated CO2 and exposed to a simulated tree fall gap is discussed in the context of the importance of gap phase regeneration for species in rain forest ecosystems and the potential effects of global change on those processes.

Tricarboxylic acid cycle intermediates in human muscle at rest and during prolonged cycling.

Previous studies have used the muscle concentration of citrate + malate + fumarate to estimate tricarboxylic acid (TCA) cycle pool size in humans [e.g., Am. J. Physiol. 259 (Cell Physiol. 28): C834-C841, 1990]. Our purpose was to quantify changes in individual TCA cycle intermediates (TCAI) and total pool size by measuring the concentrations of the eight TCAI in human muscle. Eight males cycled to exhaustion (Exh) at approximately 70% of their maximal oxygen uptake, and biopsies were obtained from the vastus lateralis at rest and during exercise. Succinyl-CoA was not consistently detectable, but the sum of the other seven TCAI was 1.23 +/- 0.04 mmol/kg dry wt at rest, 4.80 +/- 0.25 and 4.87 +/- 0.30 mmol/kg after 5 and 15 min of exercise, respectively, and 3.08 +/- 0.15 mmol/kg at Exh. Pool size during exercise was approximately 50% higher than that seen in rodent muscle after intense electrical stimulation (Eur. J. Biochem. 110: 371-377, 1980). Relative changes in individual TCAI were not uniform, and no one intermediate was "representative" of the changes in total pool size. We conclude that changes in specific intermediates or total pool size cannot be used as indicators of cycle flux and that the apparent species differences in total pool size may reflect differences in fiber type composition, recruitment pattern, or relative intensity of contraction.

Steady-state regulation of whole-body thyroid hormone pool sizes and interconversion rates in hypothyroid and moderately T3-stimulated rats.

Steady-state regulation of whole-body T3 and T4 distribution and metabolism were directly evaluated and compared in hypothyroid, euthyroid, and in euthyroid rats moderately T3-stimulated by continuous infusion of 0.15 microg/day L-T3 per 100 g BW, thereby supplementing euthyroid T3 sources by two thirds. Our goal was to develop deeper insights into the hierarchy, quantitative adequacy, and sensitivity of this regulatory system, in response to these hormone production challenges in constant steady state. We used a novel whole-body steady-state experiment design model and data analysis approach, which entails nonexclusive whole-body homogenate extracts and blood collected after 7-day infusions of tracer T3 (T3*) or T4*, quantitatively analyzed chromatographically for T3*, T4* and metabolite* concentrations. Hormone regulation implications across the 3 groups were assessed by comparing (per 100g BW) total body T4 to T3 and T3 from T4 conversion rates (CR(4-3) and CR(3-4)), total body pool sizes (Qtot) and distribution volumes (V(D)), total body production (PR), or plasma appearance rates (PAR), plasma clearance rates (PCR), and elimination rates (k). In the hypothyroid rats, absolute production of T3 from T4 was only a fourth of that in euthyroids: CR(3-4) = 1.55 vs. 6.77 ng/h, but the percent (efficiency) of whole-body T4 converted to T3 was more than double that in euthyroids: %CR(4-3) = 45.4% vs. 21.0%, reflecting an effective doubling of type I and/or type II 5'-deiodinase activity on a whole-body basis in response to severe curtailment of thyroidal production. Whole-body T3 pools and T3 production and clearance rates were all about 2 to 3 times lower in hypo- than in euthyroids: minimum Qtot = 36.8 vs. 100 ng, V(D3) = 148 vs. 236 ml, PAR3 = 3.44 vs. 9.09 ng/h, PCR3 = 13.8 vs. 21.3 ml/h; and nearly all T4 pool size, production, clearance and elimination rates also were very substantially reduced: PCR4 = 0.540 vs. 0.941 ml/h, PR4 = 4.11 vs. 38.3 ng/h, Qtot4 = 128 vs. 702 ng, k4 = 0.0322 vs. 0.0530 h(-1). In moderately T3-stimulated rats, presumed central feedback effects of the added T3 on T4 production and total body pool size also were quite pronounced: PR4 = 21.4 ng/h and Qtot4 = 346 ng were reduced to about half that in euthyroids, but T4 elimination indices were virtually unchanged, and T3 production and elimination were minimally affected. Thus, overall, stabilizing negative feedback regulation of TH functioning at different hierarchical levels is quite bidirectionally sensitive. We found very tight (inhibitory) control over thyroidal T4 secretion, possibly also T3 secretion, and probably also absolute T3 production from T4, in response to moderate (+68%) supplements in T3 production; and the efficiency of total body T3 production from available T4 was amplified substantially in the severe primary hypothyroid state, although not nearly enough to compensate for the malady. Finally, the blood to total body pool fractions (Qb/Qtot) of both T3 and T4, but not the plasma or blood hormone levels, remained remarkably constant in response to these oppositely directed hormone production challenges, suggesting this ratio as an actively regulated, homeostatically-maintained entity.

Carbohydrate Contribution to Fruit Development in Two Phenologically Distinct Rabbiteye Blueberry Cultivars

Rabbiteye blueberry (Vaccinium ashei Reade) cultivars differ in timing of floral and vegetative budbreak and in final fruit size. For example, `Bonita' exhibits concomitant floral and vegetative budbreak and has relatively large fruit size, while floral budbreak precedes vegetative budbreak in `Climax' and fruit size is smaller. Mobilization of carbohydrate before and during fruit development in `Bonita' and `Climax' rabbiteye blueberries was examined to determine if differences in carbohydrate availability between these two cultivars were correlated with differences in fruit size. Root dry mass (DM) of both cultivars decreased from dormancy (31 days before anthesis) through fruit development. Sugar concentrations in roots and stems of both cultivars decreased significantly between dormancy and anthesis, then remained relatively steady throughout fruit development. Starch concentrations in roots and stems of `Bonita' decreased significantly between dormancy and anthesis. The extent of total starch depletion in `Climax' was similar; however, the decrease was more gradual, extending from dormancy to 28 days after anthesis (DAA); at which time, vegetative budbreak in `Climax' occurred. Thus, although total reserve carbohydrate pool sizes were similar between the two cultivars, remobilization patterns were different, resulting in increased starch mobilization in `Bonita' compared to `Climax' in the period leading up to anthesis. Concentration of 14C from reserve carbon sources was similar in flowers of both cultivars at anthesis. These values declined throughout fruit development as a result of dilution of the labeled carbon by unlabeled carbon from current photosynthesis. There was a sharper decline in 14C concentration of `Bonita' fruit compared to `Climax' fruit between anthesis and 51 DAA. This, coupled with differences in timing of vegetative budbreak between the two cultivars, suggests that `Bonita' fruit were accessing current (unlabeled) assimilate earlier (i.e., before 51 DAA) than `Climax' fruit. Smaller fruit size in `Climax' compared to `Bonita' may be a consequence of a decrease in reserve carbohydrate mobilization to `Climax' flower buds before anthesis relative to `Bonita', as well as a delay or reduction in the availability of current carbohydrates to developing `Climax' fruit between anthesis and 51 DAA.

Analysis of epithelial cell stress response during infection by Shigella flexneri

Shigella flexneri-infected macrophage cells undergo an apoptotic-like death as early as one hour after infection (A. Zychlinsky, M. C. Prévost, and P. J. Sansonetti, Nature [London] 358:167-168, 1992). To determine the fate of infected epithelial cells, we characterized the viability, morphology, and several metabolic activities of HeLa cells after treatment with M90T, an invoffve isolate of S. flexneri serotype 5, or BS176, a noninvasive isolate cured of the 220-kb virulence plasmid. Using standard assays, we found that for at least 4 h after infection with M90T, HeLa cells remained viable and did not detach or lyse. The ultrastructural morphology of HeLa cells heavily infected with M90T was free of hallmarks associated with cells undergoing apoptosis. Consistent with the idea that intracellular bacterial growth is metabolically stressful to the host cell, we observed that, compared with BS176 treated-HeLa cells, M90T-treated HeLa cells showed (i) a significant decrease in the total pool size of nucleoside triphosphates, (ii) a reduced ability to incorporate extracellular radiolabeled methionine into the soluble and insoluble cell fractions, and (iii) a stimulation of glucose uptake. However, there was no detectable increase in expression of the stress-inducible hsp70 gene in M90T-infected HeLa cells or activation of the anaerobic metabolic pathway as determined by measuring total lactate levels. These results demonstrate clearly that the fate of S.flexneri-infected cells can vary dramatically between cell types and agree with the hypothesis that the destruction of epithelial cells observed in experimental models of shigellosis is due to the host inflammatory response and probably not bacterial intracellular multiplication per se.

Slow intestinal transit: a motor disorder contributing to cholesterol gallstone formation in the ground squirrel.

Impaired gallbladder motility is an established factor in cholesterol gallstone formation. We assessed whether altered small intestinal smooth muscle contractility with slow transit might potentiate gallstone formation by further impeding enterohepatic cycling of bile acids. Ground squirrels were fed a 1% or a trace (controls) cholesterol diet. Small intestinal transit was evaluated from 51Cr distribution in conscious, fasted animals 20 minutes after infusion into the proximal jejunum. Small intestinal and gallbladder smooth muscle contractility was determined in vitro. Biliary lipid secretion was measured from the cannulated common duct and the bile salt pool size calculated by isotope dilution. Gas-liquid chromatography (GLC) assessed bile salt profile. In animals on the 1% cholesterol diet, aboral transit was significantly delayed, the maximal contractile response to bethanechol was markedly increased (P <.05) with no change in median effective concentration in either circular or longitudinal muscle strips from both the jejunum and ileum, and the gallbladder contractile responses to bethanechol and cholecystokinin (CCK) were decreased. Cholesterol saturation index and the fraction of deoxycholic acid in the pool doubled, whereas the total bile salt pool size remained unchanged in cholesterol-fed animals. In this model, a high-cholesterol diet is associated with altered small intestinal smooth muscle contractility and prolonged small intestinal transit, in addition to diminished gallbladder contractility. The resulting sluggish enterohepatic cycling of bile salts, associated with expanded deoxycholate pool, contributes to cholesterol gallstone formation.

Slow intestinal transit: A motor disorder contributing to cholesterol gallstone formation in the ground squirrel

Impaired gallbladder motility is an established factor in cholesterol gallstone formation. We assessed whether altered small intestinal smooth muscle contractility with slow transit might potentiate gallstone formation by further impeding enterohepatic cycling of bile acids. Ground squirrels were fed a 1% or a trace (controls) cholesterol diet. Small intestinal transit was evaluated from 51Cr distribution in conscious, fasted animals 20 minutes after infusion into the proximal jejunum. Small intestinal and gallbladder smooth muscle contractility was determined in vitro. Biliary lipid secretion was measured from the cannulated common duct and the bile salt pool size calculated by isotope dilution. Gas-liquid chromatography (GLC) assessed bile salt profile. In animals on the 1% cholesterol diet, aboral transit was significantly delayed, the maximal contractile response to bethanechol was markedly increased (P <.05) with no change in median effective concentration in either circular or longitudinal muscle strips from both the jejunum and ileum, and the gallbladder contractile responses to bethanechol and cholecystokinin (CCK) were decreased. Cholesterol saturation index and the fraction of deoxycholic acid in the pool doubled, whereas the total bile salt pool size remained unchanged in cholesterol-fed animals. In this model, a high-cholesterol diet is associated with altered small intestinal smooth muscle contractility and prolonged small intestinal transit, in addition to diminished gallbladder contractility. The resulting sluggish enterohepatic cycling of bile salts, associated with expanded deoxycholate pool, contributes to cholesterol gallstone formation. (Hepatology 1996 Jun;23(6):1664-72)

Microbial biomass C, N and P in two arctic soils and responses to addition of NPK fertilizer and sugar: implications for plant nutrient uptake.

The soil microbial carbon (C), nitrogen (N) and phosphorus (P) pools were quantified in the organic horizon of soils from an arctic/alpine low-altitude heath and a high-altitude fellfield by the fumigation-extraction method before and after factorial addition of sugar, NPK fertilizer and benomyl, a fungicide. In unamended soil, microbial C, N and P made up 3.3-3.6%, 6.1-7.3% and 34.7% of the total soil C, N and P content, respectively. The inorganic extractable N pool was below 0.1% and the inorganic extractable P content slightly less than 1% of the total soil pool sizes. Benomyl addition in spring and summer did not affect microbial C or nutrient content analysed in the autumn. Sugar amendments increased microbial C by 15 and 37% in the two soils, respectively, but did not affect the microbial nutrient content, whereas inorganic N and P either declined significantly or tended to decline. The increased microbial C indicates that the microbial biomass also increased but without a proportional enhancement of N and P uptake. NPK addition did not affect the amount of microbial C but almost doubled the microbial N pool and more than doubled the P pool. A separate study has shown that CO2 evolution increased by more than 50% after sugar amendment and by about 30% after NPK and NK additions to one of the soils. Hence, the microbial biomass did not increase in response to NPK addition, but the microbes immobilized large amounts of the added nutrients and, judging by the increased CO2 evolution, their activity increased. We conclude: (1) that microbial biomass production in these soils is stimulated by labile carbon and that the microbial activity is stimulated by both labile C and by nutrients (N); (2) that the microbial biomass is a strong sink for nutrients and that the microbial community probably can withdraw substantial amounts of nutrients from the inorganic, plant-available pool, at least periodically; (3) that temporary declines in microbial populations are likely to release a flush of inorganic nutrients to the soil, particularly P of which the microbial biomass contained more than one third of the total soil pool; and (4) that the mobilization-immobilization cycles of nutrients coupled to the population dynamics of soil organisms can be a significant regulating factor for the nutrient supply to the primary producers, which are usually strongly nutrient-limited in arctic ecosystems.

Pyridine nucleotide levels and activities of dehydrogenases in cambial derivatives ofRobinia pseudoacacia L.

Despite the importance of the vascular cambial differentiation, little is known about its regulation. In order to address this problem we attempted to biochemically characterize differentiating xylem and phloem elements during the early stages of development. By applying techniques of quantitative histochemistry we show that the total pool size of pyridine nucleotides is similar in the phloem (PD) and xylem (XD) oriented derivatives of the cambial zone of trees ofRobinia pseudoacacia L. Within the PD zone, the amount of NAD + NADH exceeded that of NADP + NADPH [around 600 versus 200 pmol (mg dry weight)-1], possibly indicative of a preponderance of catabolic pathways (ratio of NADH∶NAD about 1). In contrast, the NADP(H) system dominated in the XD zone. This coincided with a high activity of NAD kinase. In addition, the extractable activities of the key enzymes of the oxidative pentose phosphate pathway, glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase, were greatly increased. At a ratio of NADPH∶NADP of approximately 1, this could be indicative of increased rates of reductive biosyntheses, and could thus well be involved in early steps of the formation of phenols and lignin monomers. Taken together, this first approach clearly shows that phloem-oriented and xylem-oriented cambial descendents exhibit distinct differences in their biochemical patterns even in early stages of differentiation.

Role of skeletal muscle sodium pumps in the adaptation to potassium deprivation

Skeletal muscle is specialized to lose K+ to the extracellular fluid during potassium deprivation which buffers the fall in plasma K+ concentration. While it remains to be determined whether K+ efflux from muscle is altered during K+ deprivation, active K+ uptake driven by sodium pumps is significantly depressed. The activity of sodium pumps in skeletal muscle does not increase during K+ depletion despite elevated intracellular Na+, a strong stimulus to increase activity in other cells. There is a decrease in the total pool size of sodium pump alpha beta heterodimers during potassium deprivation. The alpha 2 (not the alpha 1) sodium pump isoform is specifically decreased and beta 1 and/or beta 2 decreases in a muscle-fibre-dependent manner. The specific loss of K+ from skeletal muscle is probably a consequence of the fact that the alpha 2 isoform predominates in this tissue. In tissues such as heart, where alpha 2-type pumps are only a minor fraction of the sodium pumps, the activity of the ubiquitous alpha 1 isoform maintains intracellular Na+ and K+ at control levels, despite the fact that alpha 2 levels decrease by 50%. Analysis of the time course of change in alpha 2 mRNA vs. protein during K+ deprivation indicates that there is both a decrease in alpha 2 synthesis and an increase in alpha 2 degradation. The apparent time-lag during potassium deprivation between the early decreases in both surface alpha 2-type sodium pump number (assessed by 3H-ouabain binding) and intracellular K+, and the later decrease in total pool size of alpha 2, suggests the hypothesis that there may be an early internalization of alpha 2 sodium pumps to endosomal pools, followed by a degradation of these internalized pumps, contributing to the decrease in total alpha 2 pool size. The signals mediating this specific response to hypokalemia, and those mediating the restoration of muscle K+ stores remain to be determined.

N, K and P deficiency in chronosequential cut summer-dry grasslands on gley podzol after the cessation of fertilizer application

With the intensification of agricultural practices, formerly species rich marginal grassland communities of high botanical value in the Netherlands have been fertilized or manured since the first part of the twentieth century. This type of land use resulted in a dramatic decrease of the original plant species-richness. In the early 1970's yearly nutrient input to many of these grasslands was ceased as a nature management practice, while hay-cropping was continued. This type of grassland management is carried out to decrease overall nutrient supplying ability of the soil to plant cover in order to restore their original high botanical richness. The effect of this management on the type and the extent of nutrient deficiency was studied by comparing the short-term shoot responsiveness of undisturbed turfs to added nutrients and the nutrient status of fieldgrown dominants of four hay-field communities which were not fertilized for 3, 7, 20 or 25 years. Contrary to expectation, hay-cropping without input of additional nutrients did not impose an increase of species-richness of grassland on gley podzol. During early vegetation change strong inadequacy of N supply and moderate inadequacy of K supply by the soil regulate (shoot) growth. P-deficiency was not established. Prolonged discontinuation of fertilizer application caused concomitant inadequate supplies of N, K and P. In the last field (25 years unfertilized), nutrient deficiencies could not be detected by shoot growth responses to added nutrients but only by a low nutrient status. It appeared that during this type of vegetation change N-deficiency is the most pronounced and that K-deficiency developes much more rapidly than P-deficiency. The strong decline in total aerial pool sizes of N, K and P also emphasizes these simultaneously occurring shifts. We conclude that cut grassland composition on gley podzol soil is regulated by co-deficiencies of at least the soil phytoavailable macronutrients nitrogen, potassium and phosphorus. The absence of change in plant species number is likely not regulated by the nutrient supplying ability of the soil. Seed dispersal from elsewhere seems to be the most important factor.

Simulated effects of atmospheric deposition, harvesting, and species change on nutrient cycling in a loblolly pine forest

The effects of atmospheric deposition (current, 50% sulfur (S) deposition, and 200% nitrogen (N) deposition), harvest, and species change (from loblolly pine ( Pinus taeda L.) to mixed oak) on nutrient cycling were simulated for Duke Forest, North Carolina, using the Nutrient Cycling Model. Based upon the literature, we hypothesized that: (1) changes in S and N deposition would cause only minor changes in leaching rates and soil exchangeable cation pools because of ecosystem buffering of S and N; (2) replacement of loblolly pine by hardwoods would cause depletion of exchangeable Ca 2+, reduced Ca 2+ leaching and increased Mg 2+ leaching because of high rates of Ca uptake by hardwoods; (3) total Ca export via leaching and whole-tree harvesting in the hardwood and loblolly pine stands would be similar because lower Ca removal in harvest would be offset by greater Ca 2+ loss by leaching in the loblolly pine stand. Hypothesis I was supported by the results of the simulations: atmospheric deposition scenarios caused minor (typically < 5%) changes in leaching rates and soil exchangeable cation pools. However, changes in atmospheric deposition did cause large changes in simulated soil solutions and exchangeable cation concentrations in surface horizons, where total pool sizes were relatively small. Thus, although the simulation results suggest that the changes in S and N deposition will have little effect upon total leaching losses and nutrient pool sizes, they do not imply that atmospheric deposition has negligible effects upon exchangeable base cation concentrations. Hypothesis II was supported by the simulation results. At the end of the 20 year simulations, soil exchangeable Ca 2+ and Ca 2+ leaching were greatly reduced by hardwoods. However, Hypothesis III was not supported: cumulative Ca 2+ leaching in the hardwood stand was only slightly (16%) less than in the loblolly stand, and total Ca export via leaching and whole-tree harvesting was considerably greater in the hardwood stand than in the loblolly pine stand. The patterns in Ca and Mg distribution and leaching in the simulations were very similar to the field results from near Oak Ridge, Tennessee. The simulation results suggest that nutrient budget analysis using only a few years of leaching data extrapolated over a full rotation can be very misleading because of changes in leaching rate with time.

The effect of protein degradation products in grass silages on feed intake and intake behaviour in sheep

The effects of NH3 and amines on grass-silage intake, intake behaviour and rumen characteristics were studied in sheep. From a single sward, two direct-cut grass silages were prepared, either untreated (WAS) or with 4.51 formic acid/tonne (FAS). Four experimental diets: WAS, FAS, FAS with addition of 2.9 g NH3/kg DM (FAS + N) and FAS with 2.8 g amines/kg DM (FAS + A), were offered ad lib. once daily to four rumen-cannulated wethers in a 4 x 4 Latin square design. Daily DM intake (DMI) tended to be influenced by dietary treatment (P = 0.09). Compared with FAS, DMI was lower for WAS. Addition of NH3 did not alter DMI, whereas amine addition slightly lowered daily DMI. Reduced DMI resulted from lower intake rates during both the principal meal and the subsequent small meals. Lower initial intake rate during the principal meal suggested reduced palatability of WAS and FAS + A. Amines and NH3, however, did not influence chewing efficiency. No treatment effects were observed on total rumen pool size, DM and neutral-detergent fibre content. Furthermore, NH3 and amines did not alter rumen pH, NH3 and volatile fatty acid concentrations to the extent that they could act on chemostatic intake regulation. Amine addition, however, lowered osmolality of the rumen liquid. No treatment effects on rumen motility were observed. In conclusion, daily DMI was not reduced by the addition of NH3, suggesting that NH3 per se is not the causal factor in the negative correlations between silage NH3 content and intake observed by other authors. Amines, however, tended to reduce DMI only by their effect at the oro-pharyngeal level of intake control.

Dietary Psyllium Hydrocolloid and Pectin Increase Bile Acid Pool Size and Change Bile Acid Composition in Rats

AbstractBile acid composition, synthetic rate and pool size were determined in rats fed diets containing 5 g cellulose, 5 g pectin or 5 g psyllium hydrocolloid/100 g diet using the washout technique. Bile acid pool sizes were similar for pectin- and psyllium-fed rats, and both were higher than the pool size for rats fed cellulose (5.48 ± 1.22, 4.70 ± 0.71 and 1.77 ± 0.41 µmol/100 g body wt, respectively). Bile acid secretion rates showed a similar pattern [1730 ± 496, 1551 ± 252 and 572 ± 88 nmol/(h·100 g body wt)], as did basal synthetic rates [129 ± 25, 126 ± 42 and 87 ± 18 pmol/(h·100 g body wt)]. Individual and total bile acid pool sizes were generally higher in animals fed the pectin- or psyllium-supplemented diet compared with rats fed cellulose. Pectin or psyllium consumption resulted in a lower hydrophobicity of the bile acid pool and a lower ratio of circulating 12α-hydroxylated to non-12α-hydroxylated bile acids compared with cellulose consumption. This reduced hydrophobicity has been shown to reduce feedback inhibition of bile acid synthesis and may be responsible for the larger bile acid pool size. Changes in the location of reabsorption of bile acids may also be responsible for changes in the pool size and composition. These changes are characteristic of greater sterol excretion