Gene amplification at a locus encoding a putative Na+/H+ antiporter confers sodium and lithium tolerance in fission yeast.

We have identified a new locus, sodium 2 (sod2) based on selection for increased LiCl tolerance in fission yeast, Schizosaccharomyces pombe. Tolerant strains have enhanced pH-dependent Na+ export capacity and sodium transport experiments suggest that the gene encodes an Na+/H+ antiport. The predicted sod2 gene product can be placed in the broad class of transporters which possess 12 hydrophobic transmembrane domains. The protein shows some sequence similarity to the human and bacterial Na+/H+ antiporters. Overexpression of sod2 increased Na+ export capacity and conferred sodium tolerance. Osmotolerance was not affected and sod2 cells were unaffected for growth in K+. In a sod2 disruption strain cells were incapable of exporting sodium. They were hypersensitive to Na+ or Li+ and could not grow under conditions that approximate pH7. The sod2 gene amplification could be selected stepwise and the degree of such amplification correlated with the level of Na+ or Li+ tolerance.     

Headache at high altitude is not related to internal carotid arterial blood velocity

The cause of headache in persons going to high altitude is unknown. Relatively severe hypoxemia in susceptible subjects could induce large increases in cerebral blood flow that then could initiate the headache. Thus we measured noninvasively, by Doppler ultrasound, changes in internal carotid arterial blood velocity (velocity) in 12 subjects in Denver (1,600 m) and repeatedly up to 7 h at a simulated altitude of 4,800 m (barometric pressure = 430 Torr). Six subjects, selected because of prior history of high-altitude headache, developed comparatively severe headache at 4,800 m, and four subjects, without such history, remained well. Two subjects developed moderate headache. Velocity at 4,800 m did not correlate with symptom development, arterial O2 saturation, or end-tidal PCO2. Also, neither velocity nor blood pressure was consistently elevated above the Denver base-line values. During measurements of hypercapnic ventilatory response in Denver, velocity increased linearly with end-tidal PCO2, confirming that our Doppler method could demonstrate an increase. Also, 30 min of isocapnic or poikilocapnic hypoxia caused small increases in velocity (+8 and +6%) during the base-line measurement at low altitude. Although even a small increase in cerebral perfusion could contribute to headache symptoms at high altitude, cerebral blood flow does not appear to play a primary role.     

Oxygen transport during steady-state submaximal exercise in chronic hypoxia

Arterial O2 delivery during short-term submaximal exercise falls on arrival at high altitude but thereafter remains constant. As arterial O2 content increases with acclimatization, blood flow falls. We evaluated several factors that could influence O2 delivery during more prolonged submaximal exercise after acclimatization at 4,300 m. Seven men (23 +/- 2 yr) performed 45 min of steady-state submaximal exercise at sea level (barometric pressure 751 Torr), on acute ascent to 4,300 m (barometric pressure 463 Torr), and after 21 days of residence at altitude. The O2 uptake (VO2) was constant during exercise, 51 +/- 1% of maximal VO2 at sea level, and 65 +/- 2% VO2 at 4,300 m. After acclimatization, exercise cardiac output decreased 25 +/- 3% compared with arrival and leg blood flow decreased 18 +/- 3% (P less than 0.05), with no change in the percentage of cardiac output to the leg. Hemoglobin concentration and arterial O2 saturation increased, but total body and leg O2 delivery remained unchanged. After acclimatization, a reduction in plasma volume was offset by an increase in erythrocyte volume, and total blood volume did not change. Mean systemic arterial pressure, systemic vascular resistance, and leg vascular resistance were all greater after acclimatization (P less than 0.05). Mean plasma norepinephrine levels also increased during exercise in a parallel fashion with increased vascular resistance. Thus we conclude that both total body and leg O2 delivery decrease after arrival at 4,300 m and remain unchanged with acclimatization as a result of a parallel fall in both cardiac output and leg blood flow and an increase in arterial O2 content.(ABSTRACT TRUNCATED AT 250 WORDS)     

Removal of 3'-phosphoglycolate from DNA strand-break damage in an oligonucleotide substrate by recombinant human apurinic/apyrimidinic endonuclease 1.

A recombinant human AP endonuclease, HAP1, was constructed and characterized with respect to its ability to recognize and act upon a model double-stranded 39-mer oligodeoxyribonucleotide substrate containing a strand break site with 3'-phosphoglycolate and 5'-phosphate end-group chemistries. This oligodeoxyribonucleotide substrate exactly duplicates the chemistry and configuration of a major DNA lesion produced by ionizing radiation. HAP1 was found to recognize the strand break, and catalyze the release of the 3'-phosphoglycolate as free phosphoglycolic acid. The enzyme had a Vmax of 0.1 fmole/min/pg of HAP1 protein, and a Km of 0.05 microM for the 3'-phosphoglycolate strand break lesion. The mechanism of catalysis was hydrolysis of the phosphate ester bond between the 3'-phosphoglycolate moiety and the 3'-carbon of the adjacent dGMP moiety within the oligonucleotide. The resulting DNA contained a 3'-hydroxyl which supported nucleotide incorporation by E. coli DNA polymerase I large fragment. AP endonucleolytic activity of HAP1 was examined using an analogous double-stranded 39-mer oligodeoxyribonucleotide substrate, in which the strand break site was replaced by an apyrimidinic site. The Vmax and Km for the AP endonuclease reaction were 68 fmole/min/pg of HAP1 protein and 0.23 microM, respectively.     

The biological control of snail intermediate hosts of schistosomiasis by fish

Summary The use of molluscivorous fish for biological control of snail intermediate hosts of schistosomiasis is a regularly reappearing theme in the literature on schistosomiasis control. The effectiveness of this control method has not yet been demonstrated, and conclusive field evidence is lacking. In this article the literature on snail control by fish is critically reviewed. Special attention is paid to the cichlid fish Astatoreochromis alluaudi that has been used in well-documented field trials in Kenya and Cameroon. After some small initial success, after a longer period the fish appeared to be ineffective in snail control. Moreover, the fish reproduces at a pace too slow to be of use in large-scale biocontrol trials. Laboratory observations on foraging behaviour and anatomy of the fish give essential cues to explain the failure of the fish in snail control. An observed reduction in the fishes' pharyngeal jaw apparatus, used to crush snails shells, results in a lower profitability of snails. As predicted by a simple foraging model, the prey preference of the fish shifts towards other more profitable prey items, such as benthic and pelagic macrofauna. Although eradication of snails by fish will not be feasible in most cases, the role of natural predators of snails cannot be neglected, and may still be of importance in integrated control efforts.     

Mature Tissue and Crop Canopy Respiratory Characteristics of Rye, Triticale and Wheat

Crop dry matter and its chemical composition, together withcanopy and mature tissue respiration rates were measure at equivalentgrowth stages and temperatures for spring and winter rye, triticaleand wheat crops grown under irrigated field conditions. Canopyrespiration was partitioned into growth and maintenance respirationusing information from the chemical composition analysis ofthe crop biomass. Rates of dry matter accumulation early inthe growing season were significantly greater for rye cropsin comparison to triticale and wheat. However, when dry matterwas measured at similar ontogenetic stages, the productivityadvantage of the rye crop was no longer evident. Nevertheless,canopy respiration rates per unit ground area were significantlylower for rye than wheat over all temperatures and growth stages.Intergeneric differences in the respiration rates of matureleaf and stem tissues were consistent with those measured atcanopy scales. Differences in the chemical composition of thebiomass among genera were minimal, and insufficient to accountfor differences in canopy respiration due to synthesis respirationrequirement. Estimates of biomass maintenance requirements appearto be significantly lower for rye than wheat when calculatedat similar temperatures and ontogenetic stages. The maintenancecoefficient (m) depended on stage of development, suggestingthat m will decline earlier chronologically for rye than wheat,which implies that greater carbon retention is another aspectcontributing to the higher early-season crop growth rates ofspring and winter rye. Considering the lower respiration ratesof mature stems relative to leaves, the dependence of m on stem:leafratio was suggested as a useful approach to modelling ontogeneticeffects on maintenance respiration.Copyright 1993, 1999 AcademicPress Rye, triticale, wheat, dry matter, growth and maintenance respiration