Body Position,Age and Mass Effect of Adiposity on Adipose Tissue Red Cell Flux in Morbid Obesity

Objective: To measure red cell flux of adipose tissue in morbidly obese patients' pannus in the upright and supine position to determine factors which would render the lower pannus susceptible to ischemic necrosis. Design: A cohort study of morbidly obese subjects without ischemic necrosis. Setting: University teaching hospital. Patients: Twenty-three consecutive morbidly obese patients referred for gastroplasty. Measurements: Red cell flux, measured as RMS voltage by a laser Doppler velocimeter. An optical fiber with a tip diameter of 250μ was inserted into the upper and lower pannus and output recorded in the upright and supine positions. Other variables recorded were age, BMI, blood pressure and serum lipids. Results: Adipose tissue red cell flux demonstrates considerable spatial and temporal heterogeneity from subject to subject and in various locations in the pannus. No differences in red cell flux were detected in response to change in position. However, regression analysis demonstrated that the gradient between the upper and lower abdomen in the supine position was increasingly positive with age and in the upright position it was increasingly positive with increasing weight or BMI. Conclusions: These data suggest that red cell flux is heterogeneously distributed in the abdominal pannus and is not greatly influenced by body position. However, with increasing age and adiposity there is a gradient for decreased red cell flux to the lower portion of the pannus. This may be a factor in rendering this part of the pannus prone to ischemic fat necrosis.     

Carbon flux and diversity of nematodes and termites in Cameroon forest soils

Theoretically, there are three principal ways in which ecosystem processes might respond to reductions in species richness. These theories are reviewed, and then considered in the context of a study of the diversity of soil nematodes and termites in near-primary forest sites at Mbalmayo, Cameroon, and the contribution made by these two taxa to carbon fluxes (CO₂ and CH₄) from the forest floor. Nematode abundances average 2.04 × 10⁶ m^-2, and termites between 2933 and 6957 m^-2. The site is the most species-rich yet investigated for both groups anywhere in the world, so that a very large number of species contribute to carbon fluxes. We speculate about how much redundancy might be built into the functioning of both assemblages, and point out the enormous difficulties of resolving such questions, and of producing such detailed species-inventories.     

Assessing the impact of ozone on photosynthesis of European beech (Fergus sylvatica L.) in environmental chambers

An exposure — response study with proportionalto-ambient ozone levels was conducted in closed chambers on 3-year-old European beech (Fagus sylvatica L.) of montane origin. The fumigation started in April 1990 and lasted for a single growing season. Climate data and ozone concentrations monitored at an experimental station of the Institute for Applied Plant Biology, Schönenbuch, Switzerland were simulated in the exposure chambers 12 days later (1*O₃). To test exposure-response relations three additional treatments were applied, subambient (0.2*O₃) and two proportionally increased ozone treatments (1.5*O₃ and 2*O₃). The photosynthetic behaviour of the trees in August revealed the light reactions to be less affected than parameters which are related to the dark reactions of photosynthesis. Assimilation (A₃₅₀), apparent carboxylation efficiency (CE), and maximum photosynthetic capacity (A₂₅₀₀) were reduced with increasing ozone concentration. For the ozone response of CE and A₂₅₀₀ Critical Levels were calculated.     

Compartmentation and flux characteristics of nitrate in spruce

The radiotracer¹³N was used to undertake compartmental analyses for NO ₃ ^– in intact non-mycorrhizal roots ofPicea glauca (Moench) Voss. seedlings. Three compartments were defined, with half-lives of exchange of 2.5 s, 20 s, and 7 min. These were identified as representing surface adsorption, apparent free space, and cytoplasm, respectively. Influx, efflux, and net flux as well as cytoplasmic and apparent-free-space nitrate concentrations were estimated for three different concentration regimes of external nitrate. After exposure to external NO ₃ ^– for 3 d, influx was calculated to be 0.09 mol·g^–1·h^–1 (at 10 M [NO ₃ ^– ]_o), 0.5mol·g^–1·h^–1 (at 100 M [NO _inf3 ^sup– ]_o), and 1.2 mol · g^–1· h^–1 (at 1.5 mM [NO ₃ ^– ]_o). Efflux increased with increasing [NO ₃ ^– ]_o, constituting 4% of influx at 10 M, 6% at 100 M, and 21% at 1.5 mM. Cytoplasmic [NO ₃ ^– ] was estimated to be 0.3 mM at 10 uM [NO ₃ ^– ]_o, 2mM at 100 M [NO ₃ ^– ]_o, and 4mM at 1.5 mM [NO ₃ ^– ]_o, while free-space [NO ₃ ^– ] was 16 M, 173 M, and 2.2 mM, respectively. A series of experiments was carried out to confirm the identity of the compartments resolved by efflux analysis. Pretreatment at high temperature or application of 2-chloro-ethanol, sodium dodecyl sulphate or hydrogen peroxide made it possible to distinguish the metabolic (cytoplasmic) phase from the remaining two (physical) phases. Likewise, varying [Pi] of the medium altered efflux and thereby [NO ₃ ^– ]_cyt, but did not affect [NO ₃ ^– ]_{free space}.Abbreviations and Symbols [NO ₃ ^– ]_cyt cytoplasmic NO ₃ ^– concentration - [NO ₃ ^– ]_{free space} apparent-free-space NO ₃ ^– concentration - [NO ₃ ^– ]_o concentration of NO ₃ ^– in the external solution - NO ₃ ^– flux - _co efflux from the cytoplasm - _oc influx to the cytoplasm - _net net flux - _xylem flux to the xylem - _red/vac combined flux to reduction and the vacuole The research was supported by a Natural Sciences and Engineering Research Council, Canada, grant to Dr. A.D.M. Glass and by a University of British Columbia Graduate Fellowship to Herbert J. Kronzucker. Our thanks go to Dr. M. Adam and Mr. P. Culbert at the particle accelerator facility TRIUMF on the University of British Columbia Campus for providing¹³NO ₃ ^– , Drs. R.D. Guy and S. Silim for providing plant material, and Dr. M.Y. Wang, Mr. J. Mehroke and Mr. P. Poon for assistance in experiments and for helpful discussions.     

Proton flux measurements from tissues in buffered solution

Proton movement across plant cell membranes is part of many important physiological processes. The net proton flux to or from tissues can be determined non-invasively by measuring the proton electrochemical potential gradient in the adjacent solution. In buffered solution, some of the protons crossing the tissue boundary diffuse as proto-nated buffer whose flux is not included in the flux calculated from the proton (hydrogen ion) electrochemical gradient. In this theoretical paper, it is shown how experimenters can calculate the protonated buffer flux from the measured proton flux in solution. The ratio of these two components of total proton flux depends on the pH of the solution and on the concentration and pK of the buffer. For a given concentration of a buffer which has a single pK, the flux ratio rises with pH when the solution pH is lower than the buffer pK. The slope is about 2 on a log₁₀ scale. As the pH increases above the pK, the flux ratio levels off to approach its maximum. With mixed buffers, or one having two or more pK values, the flux ratios are additive: each buffer acts independently based on its concentration and its pK value. Unbuffered solutions always have the buffering effects of water itself and also of carbonates due to carbon dioxide dissolved from the atmosphere. In unbuffered solutions at pH 6, the flux carried by water and carbonate is about 1 % of the measured proton flux. This validates measurements of proton flux from tissues, made by a number of workers, in unbuffered solutions below pH 6.     

GROWTH OF HETEROSIGMA CARTERAE (RAPHIDOPHYCEAE) ON NITRATE AND AMMONIUM AT THREE PHOTON FLUX DENSITIES: EVIDENCE FOR N STRESS IN NITRATE-GROWING CELLS

The marine alga Heterosigma carterae Hulburt (Raphidophyta) was grown in N-limiting batch cultures using either nitrate or ammonium as the N source, at photon flux densities (PFDs) of 50, 200, and 350 μmol·m^-2·s^-1 in a 12:12 h LD cycle. Carbon content could be estimated from biovolume (μg C = 0.278 × nL; R = 0.98) but not reliably from pigment content. During exponential growth, ammonium-grown cells (in comparison with nitrate-grown cells at the same PFD) attained higher growth rates by at least 20%, contained more N, and had a lower C:N ratio, higher concentrations of intracellular free amino acids, and higher ratios of glutamine: glutamate (Gln: Glu) and asparagine: aspartate (Asn:Asp). Growth was nearly light-saturated on ammonium at 200 μmol·m^-2·s^-1 (cell-specific growth rate of 1.2 d^-1) but probably not saturated in nitrate-grown cells at 350 μmol·m^-2·s^-1. PFD did not affect Gln: Glu or Asn: Asp for a given N source. These results indicate that the nitrate-growing cells were more N-stressed than those using ammonium (which in contrast were relatively C-stressed) and that this organism would show an enhanced competitive advantage against other species when supplied with a transient supply of ammonium rather than nitrate .     

Seasonal activity and energetics of two species of varanid lizards in tropical Australia

The field metabolic rates (FMR) and rates of water flux were measured in two species of varanid lizards over five periods of the year in tropical Australia. The energetics of these species were further investigated by directly measuring activity (locomotion) and body temperatures of free-ranging animals by radiotelemetry, and by measuring standard metabolic rate (over a range of body temperatures) and activity metabolism in the laboratory. Seasonal differences in the activity and energetics were found in these goannas despite similar, high daytime temperatures throughout the year in tropical Australia. Periods of inactivity were associated with the dry times of the year, but the onset of this period of inactivity differed with respect to habitat even within the same species. Varanus gouldii, which inhabit woodlands only, were inactive during the dry and late dry seasons. V. panoptes that live in the woodland had a similar seasonal pattern of activity, but V. panoptes living near the floodplain of the South Alligator River had their highest levels of activity during the dry season when they walked long distances to forage at the receding edge of the floodplain. However, during the late dry season, after the floodplain had dried completely, they too became inactive. For V. gouldii, the rates of energy expenditure were 196 kJ kg^–1 day^–1 for active animals and 66 kJ kg^–1 day^–1 for inactive animals. The rates of water influx for these groups were respectively 50.7 and 19.5 ml kg^–1 day^–1. For V. panoptes, the rates of energy expenditure were 143 kJ kg^–1 day^–1 for active animals and 56 kJ kg^–1 day^–1 for inactive animals. The rates of water influx for these two groups were respectively 41.4 and 21.0 ml kg^–1 day^–1. We divided the daily energy expenditure into the proportion of energy that lizards used when in burrows, out of burrows but inactive, and in locomotion for the two species during the different seasons. The time spent in locomotion by V. panoptes during the dry season is extremely high for a reptile (mean of 3.5 h/day spent walking), and these results provide an ecological correlate to the high aerobic capacity found in laboratory measurements of some species of varanids.     

Space proton flux and the temporal distribution of cardiovascular deaths

 The influence of solar activity (SA) and geomagnetic activity (GMA) on human homeostasis has long been investigated. The aim of the present study was to analyse the relationship between monthly proton flux (>90 MeV) and other SA and GMA parameters and between proton flux and temporal (monthly) distribution of total and cardiovascular-related deaths. The data from 180 months (1974–1989) of distribution in the Beilinson Campus of the Rabin Medical Centre, Israel, and of 108 months (1983–1991) from the Kaunas Medical Academy, were analysed and compared with SA, GMA and space proton flux (>90 MeV). It was concluded: (1) monthly levels of SA, GMA and radiowave propagation (Fof2) are significantly and adversely correlated with monthly space proton flux (>90 MeV); (2) medical-biological phenomena that increase during periods of low solar and/or geomagnetic activity may be stimulated by physical processes provoked by the concomitant increase in proton flux; (3) the monthly number of deaths related (positively or negatively) to SA are significantly and adversely related to the space proton flux (>90 MeV). Received: 14 January 1996 / Accepted: 14 October 1996     

Regulation of Metabolite Flux through Voltage-Gating of VDAC Channels

The mitochondrial outer membrane channel, VDAC, is thought to serve as the major permeability pathway for metabolite flux between the cytoplasm and mitochondria. The permeability of VDAC to citrate, succinate, and phosphate was studied in channels reconstituted into planar phospholipid membranes. All ions showed large changes in permeability depending on whether the channel was in the open or in the low conductance, ``closed' state, with the closed state always more cation selective. This was especially true for the divalent and trivalent anions. Additionally, the anion flux when the voltage was zero was shown to decrease to 5–11% of the open state flux depending on the anion studied. These results give the first rigorous examination of the ability of metabolites to permeate through VDAC channels and indicate that these channels can control the flux of these ions through the outer membrane. This lends more evidence to the growing body of experiments that suggest that the outer mitochondrial membrane has a much more important role in controlling mitochondrial activity than has been thought historically. Received: 4 November 1996/Revised: 8 January 1997     

An analysis of proton fluxes coupled to electron transport and ATP synthesis in chloroplast thylakoids

Electron transport, phosphorylation and internal proton concentration were measured in illuminated spinach chloroplast thylakoid membranes under a number of conditions. Regardless of the procedure used to vary these parameters, the data fit a simple chemiosmotic model. Protons from Photosystem II did not appear to be utilized differently from those derived from Photosystem I. The maximal phosphorylation efficiency ($\text{P}\text{e}{}_2$) for photophosphorylation in washed thylakoids under oxidizing conditions is likely to be $\text{4}\text{3}$. This value is consistent with a proton-to-electron-pair ratio of 4 for electron flow through both photosystems and a proton-to-ATP ratio of 3 for the chloroplast proton-ATPase.