Disruption of energy metabolism and smoltification during exposure of juvenile atlantic salmon (Salmo salar) to low pH

Juvenile Atlantic salmon were held for 76 days at pH 4.7 during the period when the final stages of smoltification normally occur. Control salmon (pH 6.5) had significant increases in weight, length and liver somatic index which were not observed in those held at low pH. Condition factor decreased in both groups but to a significantly greater extent in the low pH group. After 15 days levels of ADP and glucose were higher and AEC, CP and glycogen were lower in muscles of salmon exposed to low pH. These qualitative differences were maintained until the end of the experiment. ATP and total adenylate concentrations in muscle were lower after 62 days of exposure to low pH compared to controls. The levels of ATP, total adenylates, AEC and glucose were consistently higher in livers of salmon exposed to low pH than those of controls. There were no differences in liver concentrations of AMP, CP and glycogen between the two treatments or with time of exposure within each treatment. The results suggest that exposure of juvenile Atlantic salmon to low pH increased gluconeogenesis and decreased food intake to the detriment of growth.     

Analysis of 6-mercaptopurine in human plasma with a high-performance liquid chromatographic method including post-column derivatization and fluorimetric detection

A relatively simple assay with improved reliability and sensitivity for measuring levels of 6-mercaptopurine in human plasma is presented. After extraction of the compound and the added internal standard with phenyl mercury acetate, samples were separated by ion-pair reversed-phase high-performance liquid chromatography. On-line the analytes were oxidized to fluorescent products and detected in a flow-fluorimeter. The within-day coefficient of variation was 3.8% at a concentration of 25 ng/ml. The lower detection limit was 2 ng/ml when 1.0 ml of plasma was used. Mercaptopurine concentration versus time curves of two subjects after a single oral dose of azathioprine are shown.     

Pollen-based biome reconstruction for southern Europe and Africa 18,000 yr bp

Pollen data from 18,000 ¹⁴C yr bp were compiled in order to reconstruct biome distributions at the last glacial maximum in southern Europe and Africa. Biome reconstructions were made using the objective biomization method applied to pollen counts using a complete list of dryland taxa wherever possible. Consistent and major differences from present‐day biomes are shown. Forest and xerophytic woods/scrub were replaced by steppe, both in the Mediterranean region and in southern Africa, except in south‐western Cape Province where fynbos (xerophytic scrub) persisted. Sites in the tropical highlands, characterized today by evergreen forest, were dominated by steppe and/or xerophytic vegetation (cf. today’s Ericaceous belt and Afroalpine grassland) at the last glacial maximum. Available data from the tropical lowlands are sparse but suggest that the modern tropical rain forest was largely replaced by tropical seasonal forest while the modern seasonal or dry forests were encroached on by savanna or steppe. Montane forest elements descended to lower elevations than today.     

Membrane electrical parameters in turtle bladder measured using impedance-analysis techniques

Summary Equivalent-circuit impedance analysis experiments were performed on the urinary bladders of freshwater turtles in order to quantify membrane ionic conductances and areas, and to investigate how changes in these parameters are associated with changes in the rate of proton secretion in this tissue. In all experiments, sodium reabsorption was inhibited thereby unmasking the electrogenic proton secretion process. We report the following: (1) transepithelial impedance is represented exceptionally well by a simple equivalent-circuit model, which results in estimates of the apical and basolateral membrane ionic conductances and capacitances; (2) when sodium transport is inhibited with mucosal amiloride and serosal ouabain, the apical and basolateral membrane conductances and capacitances exhibit a continual decline with time; (3) this decline in the membrane parameters is most likely caused by subtle time-dependent changes in cell volume, resulting in changes in the areas of the apical and basolateral membranes; (4) stable membrane parameters are obtained if the tissue is not treated with ouabain, and if the oncotic pressure of the serosal solution is increased by the addition of 2% albumin; (5) inhibition of proton secretion using acetazolamide in CO₂ and HCO ₃ ^– -free bathing solutions results in a decrease in the area of the apical membrane, with no significant change in its specific conductance; (6) stimulation of proton transport with CO₂ and HCO ₃ ^– -containing serosal solution results in an increase in the apical membrane area and specific conductance. These results show that our methods can be used to measure changes in the membrane electrophysiological parameters that are related to changes in the rate of proton transport. Notably, they can be used to quantify in the live tissue, changes in membrane area resulting from changes in the net rates of endocytosis and exocytosis which are postulated to be intimately involved in the regulation of proton transport.     

Exon skipping in the sterol 27-hydroxylase gene leads to cerebrotendinous xanthomatosis

We report a new mutation in the sterol 27-hydroxylase (CYP 27) gene in a Dutch family with cerebrotendinous xanthomatosis: a G→A transition in the splice donor site in intron 4. This mutation leads to skipping of exon 4, resulting in a loss of 66 amino acids in the CYP 27 enzyme molecule. Received: 15 March 1997 / Accepted: 26 March 1997