Presence of a Na+/H+ exchanger in brush border membranes isolated from the kidney of the spiny dogfish,Squalus acanthias

Summary A membrane fraction, rich in brush border membranes, was prepared from renal proximal tubules of the spiny dogfish,Squalus acanthias, and the sodium-proton exchange mechanism in these membrane vesicles was investigated by both a rapid filtration technique and the fluorescence quenching of acridine organe.²²Na⁺ uptake was stimulated by an outwardly directed H⁺ gradient, and was inhibited by amiloride at a single inhibitory site with an apparentK _i of approximately 1.7×10^–5 M. In the presence of an H _i ⁺ >H _o ⁺ gradient, the of the Na⁺/H⁺ exchanger were 9.7±0.8 mM and 48.0±12.0 nmol·mg protein^–1·min^–1, respectively. The uptake of Na⁺ was electroneutral in the presence of a H⁺ gradient, indicating a stoichiometry of 1. In the fluorescence studies, quenching of acridine orange occurred in the presence of an outwardly directed Na⁺ gradient which was inhibited by amiloride. Thus, an electroneutral Na⁺/H⁺ exchanger with properties similar to those found in the mammalian kidney is also present in the spiny dogfish and may contribute to the urinary acidification of this marine animal.     

N-15 in vivo NMR spectroscopic investigation of nitrogen deprived cell suspensions of the green alga Chlorella fusca

The possibility to apply N-15 in vivo NMR spectroscopy to study algal N-metabolism has been investigated. N-15 labelled cells of the green alga Chlorella fusca, subjected to nitrogen starvation and N-14 labelled cells supplied with K¹⁵NO₃ after prolonged nitrogen starvation were monitored by N-15 in vivo NMR spectroscopy at different times after the change in their nitrogen supply. During 20–40 min, necessary for the acquisition of 1 spectrum, the cells were under dark anaerobic conditions, but the relative amounts of the metabolites detected did not change. Signals from 2 acid amides, from the side chain nitrogens of arginine and lysine, from prolin as well as 4 signals from α amino groups of amino acids were detected. Besides two signals not yet reported in the literature were found. They may be due to amino compounds, but not to amino acids. The amount of free amino acids in the cells increases not only upon resupply of nitrogen starved cells with nitrate but also during the first hours after nitrate depletion. The spectra obtained from N-15 labelled autospores show that N-15 in vivo NMR spectroscopy can be applied to the investigation of N metabolism of the cells.     

Localization of vasopressin,serotonin and angiotensin II in endothelial cells of the renal and mesenteric arteries of the rat

Summary The localization of vasopressin, serotonin and angiotensin II in the endothelial cells of renal and mesenteric arteries was investigated using the pre-embedding peroxidase-antiperoxidase technique for electron microscopy. Vasopressin-and serotonin-positive endothelial cells were present in both renal and mesenteric arteries while angiotensin II-positive cells were observed in the mesenteric artery exclusively. Both arteries showed less than 10% immunoreactive cells. The lack of angiotensin II in the endothelial cells of the renal artery suggests that there may be subtle physiological differences between the renal and mesenteric arteries with respect to the local control of blood flow.     

Glomerular bypass shunts in the kidney of the Atlantic hagfish,Myxine glutinosa

Summary The vascular pathways associated with the glomerulus of the Atlantic hagfish, Myxine glutinosa have been studied by scanning electron microscopy of corroded resin casts of the vasculature. Although the overall pattern of the renal vasculature did not differ from earlier reports, a previously unreported vascular pathway which arose from the renal artery and bypassed the glomerular capillaries in 28% of glomeruli was clearly demonstrated. Glomerular bypass shunts either ran to join the loose capillary network around Bowman's capsule and thereby drain into the network of vessels associated with the mesonephric duct (ureter), or ran directly into the ureteral system of vessels and subsequently into the posterior cardinal veins. Glomerular bypass shunts which theoretically permit renal arterial blood to bypass the process of filtration may play a role in the regulation of body fluid volume.     

Interaction of alcohol and protein deficiency on rat brain synaptosomal (Na+−K+)-ATPase

Administration of low amounts of ethanol for a prolonged period increases rat brain synaptosomal (Na⁺–K⁺)-ATPase activity, the increase being less in the protein deficient rats. The adaptive mechanism to offset the stress imposed by the continued presence of ethanol seems to be depressed by low plane of nutrition. In vivo and in vitro effects of ethanol on (Na⁺–K⁺)ATPase seems to be different.     

The influence of CO2 enrichment, phosphorus deficiency and water stress on the growth, conductance and water use of Pinus radiata D. Don

Abstract. Seedlings of Pinus radiata D. Don were grown in growth chambers for 22 weeks with two levels of phosphorus, under either well-watered or water-stressed conditions at CO₂ concentrations of either 330 or 660mm³ dm^?3. Plant growth, water use efficiency and conductance were measured and the relationship between these and needle photosynthetic capacity, water use efficiency and conductance was determined by gas exchange at week 22. Phosphorus deficiency decreased growth and foliar surface area at both CO₂concentrations; however, it only reduced the maximum photosynthetic rates of the needles at 660 mm³ CO₂ dm^?3 (plants grown and measured at the same CO₂ concentration). Water stress reduced growth and foliar surface area at both CO₂ concentrations. Increases in needle photosynthetic rates appeared to be partly responsible for the increased growth at high CO₂ where phosphorus was adequate. This effect was amplified by accompanying increases in needle production. Phosphorus deficiency inhibited these responses because it severely impaired needle photosynthetic function. The relative increase in growth in response to high CO₂ was higher in the periodically water-stressed plants. This was not due to the maintenance of cell volume during drought. Plant water use efficiency was increased by CO₂ enrichment due to an increase in dry weight rather than a decrease in shoot conductance and, therefore, transpirational water loss. Changes in needle conductance and water use efficiency in response to high CO₂ were generally in the same direction as those at the whole plant level. If the atmospheric CO₂ level reaches the predicted concentration of 660 mm³ dm^?3 by the end of next Century, then the growth of P. radiata will only be increased in areas where phosphorus nutrition is adequate. Growth will be increased in drought-affected regions but total water use is unlikely to be reduced.     

Long-term effects of lactational zinc deficiency on bone mineral composition in rats fed a commercially modified Luecke diet

The purpose of this study was threefold: 1. to determine the long-term effects of interactions between lactational zinc deficiency and gender on bone mineral composition in repleted rat offspring, 2. to determine the nutritional efficacy of the second of two commercially designed, modified Luecke diets (ML2) during the gestational and lactational stress, and 3. determine the ultratrace element contents of Ralston Rodent Laboratory Chow #5001. The ML2 basal diet, based on dextrose, sprayed egg white, and corn oil contained 0.420 μg Zn/g, was supplemented with Zn (as zinc acetate) at 0 (diet 0ML2) or 30 (diet 30ML2) μg/g, and was mixed and pelleted commercially. all rat dams were fed the 30ML2 diet ad libitum during gestation. Beginning at parturition, the dams were fed either the 1. 0ML2, 2. 30ML2 (food restricted), or 3. 30ML2 (ad libitum) diets. All pups were fed the 30ML2 diet ad libitum from 23 to 40 d of age. From d 40 to 150, all pups were fed Ralston Rodent Laboratory Chow. The 30ML2 diet was found to be nutritionally efficacious; litter size and pup growth were normal and pup mortality was only 1.2%. Pups (ZD) with access to the 0ML2 diet until 23 d of age and nursed by dams fed the 0ML2 diet, when compared to pups (PF) fed restricted amounts of the 30ML2 diet, exhibited increased mortality and decreased concentrations of tibial zinc but no change in growth. Inadequate zinc nutriture during infancy, despite postlactational zinc repletion, induced imbalances in adult bone mineral metabolism. Thus, at 150 d of age, the ZD pups exhibited increased levels of bone P and Mg and decreased concentrations of K as compared to the PF pups.     

Mechanism of hypercholesterolemia produced by biotin deficiency

The effect of biotin deficiency on the metabolism of cholesterol was studied in rats fed cholesterol-free and cholesterol-containing diet. Biotin deficiency induced by feeding raw egg-white resulted in higher cholesterol in the serum and aorta, and higher high density lipoprotein cholesterol and low density lipoprotein + very low density lipoprotein cholesterol. In the liver, cholesterol increased only in the cholesterol diet group but not in the cholesterol-free diet group. Levels of triglycerides were lower in the biotindeficient, cholesterol-free diet group, but triglycerides were elevated in the cholesterol diet group. Concentration of bile acids in the liver and activity of lipoprotein lipase in the heart and adipose tissue were significantly decreased in the biotin-deficient rats. Release of lipoproteins into the circulation, incorporation of [1,2-¹⁴C] acetate into cholesterol, and activity of plasma lecithin: cholesterol acyl transferase were higher.     

Nonenzymatic isolation and culture of adult islets from atrophic pancreata of copper-deficient rats: A morphologic analysis

Summary The purpose of this study was to develop a nonenzymatic method of isolating adult islets using atrophied pancreata from copper-deficient rats and to analyze their morphologic characteristics and behavior in culture. This unusual model of isolation was studied because islets remain intact in the course of dietary copper deficiency while the acinar glandular component of the pancreas undergoes selective atrophy and lipomatosis. Small fragments containing islets were readily microdissected from atrophied glands and placed in culture. Within 24 h the fragments congealed into small irregular- to spherical-shaped masses within which the darker profile of islets could be distinguished. Within a period of 3 to 5 d, islet tissue began to bud from the lipocytic mass until by Day 7 spherical aggregates of intact islet tissue separated from the residual fragments. Subsequent to further in vitro treatment, these islets could be maintained as free viable spherical masses if periodically agitated, as attached stationary islets which developed monolayer growth if left undisturbed and as aggregated masses of islet tissue forming megaislets if combined in small groups. Grouped islets treated with actinomycin D and cycloheximide did not exhibit aggregation when incubated with these inhibitors. This suggests that megaislet formation was an active process requiring protein-RNA synthesis rather than passive clumping or aggregation that can accompany metabolically altered or dying islets undergoing cellular shedding and adhesion. Immunohistochemical localization demonstrated that insulin, glucagon, somatostatin, and pancreatic polypeptide-immunoreactive cell types were present within the islets derived from this technique. The cellular topography of these islets was not unlike that described by others for islets cultured from enzymatic isolation. This culture model may serve as a resource for mature, viable islets isolated without mechanical or enzymatic disaggregation which can have attenuating effects on islet function. This work was supported by a research grant from the Diabetes Research and Education Foundation.