Adenylate cyclase uncoupled beta-adrenergic receptors in salamander proximal tubules

The isolated perfused proximal tubule of the neotenic salamander Ambystoma tigrinum responds with either a hyperpolarization or depolarization of both the basolateral cell membrane and transepithelial potentials following the addition of 10(-5) M isoproterenol to the bath superfusate. Both responses were blocked by 10(-6) M propranolol but neither response was mimicked by 10(-4) M cAMP. beta-Adrenergic binding studies of individual microdissected proximal tubules using (-)-[3H]CGP-12177 as a hydrophyllic radioligand and (+/-)-timolol (0.1 mM) as the displacer drug revealed two distinct populations of proximal tubules possessing either low (KD = 153.8 nM; Bmax = 110.2 fM/mm) or high affinity (KD = 12.0 nM: Bmax = 3.9 fM/mm) binding characteristics. Competition studies indicated that the bound (-)-[3H]CGP-12177 behaved as a typical beta-adrenergic ligand, being displaced by (-)-isoproterenol but not by (+)-isoproterenol or (-)-phenylephrine. However, neither appeared to be coupled to the adenylate cyclase system. These data suggest the presence of functional beta-adrenergic receptors that do not appear to be coupled to the adenylate cyclase system.     

Metabolic effects of mislocalized mitochondrial and peroxisomal citrate synthases in yeast Saccharomyces cerevisiae

Genes CIT1 and CIT2 from Saccharomyces cerevisiae encode mitochondrial and peroxisomal citrate synthases involved in the Krebs tricarboxylic acid (TCA) cycle and glyoxylate pathway, respectively. A Deltacit1 mutant does not grow on acetate, despite the presence of Cit2p that could, in principle, bypass the resulting block in the TCA cycle. To elucidate this absence of cross-complementation, we have examined the ability of Cit1p to function in the cytosol, and that of Cit2p to function in mitochondria. A cytosolically localized form of Cit1p was also incompetent for restoration of growth of a Deltacit1 strain on acetate, suggesting that mitochondrial localization of Cit1p is essential for its function in the TCA cycle. Cit2p was able, when mislocalized in mitochondria, to restore a wild-type phenotype in a strain lacking Cit1p. We have purified these two isoenzymes as well as mitochondrial malate dehydrogenase, Mdh1p, and have shown that Cit2p was also able to mimic Cit1p in its in vitro interaction with Mdh1p. Models of Cit1p and Cit2p structures generated on the basis of that of pig citrate synthase indicate very high structural and electrostatic surface potential similarities between the two yeast isozymes. Altogether, these data indicate that metabolic functions may require structural as well as catalytic roles for the enzymes.     

Brain vessels in the rats exposed to primary and repeated tail-suspension. Minimization of structural changes after repeated exposure

The aim of study was histological examination of brain vessels in the rats exposed to repeated tail-suspension (TS). The rats were subjected to 30-day TS, then readapted to horizontal position for 30 days and again exposed to 14-day TS simultaneously with the rats which were underwent to 14-day TS for the first time. 30-day TS induced in brain vessels the adaptive changes hindering the excessive blood inflow to brain--spasm and hypertrophy of muscle-elastic valves in extra- and intracerebral arteries and also the destructive changes--loss of vascular tone in extra- and intracerebral arteries, plethora in extra- and intracerebral veins, intracerebral venules and capillaries, conglutination of erythrocytes in capillaries, plasmatization of veins and capillaries and edema of brain tissue pointing out in total the increase in blood inflow to the brain and difficulty of blood outflow. After 30-day readaptation of TS-rats to horizontal position only adaptive changes in extracerebral arteries and intracerebral capillaries (cell proliferation) and edema of brain tissue were revealed. After repeated, 14-day TS in spite of new redistribution of blood to the head, in contrast to the vessel alterations after primary 14-day TS, the adaptive and destructive changes in brain vessels were lack, excluding only moderate plethora of intracerebral veins, cell proliferation in capillaries and weak signs of edema.     

Characteristics of the growth on rapeseed oil and synthesis of citric and isocitric acids by <Emphasis Type="Italic">Yarrowia lipolytica</Emphasis> yeasts

The native strain Yarrowia lipolytica VKMY-2373 grown in a complete medium exhibited the maximum lipase activity at the concentration of rapesseed oil of at least 5.0 g/l. In the course of yeast growth, no considerable changes were observed in the glycerol concentration, the proportions of the major free fatty acids formed via oil hydrolysis, or the fatty acid composition of oil. Under nitrogen limitation of cell growth, the accumulation of citric acids reached 77.1 g/l with predominance of isocitric acid at pH 6.0, whereas at pH 4.5, almost equal amounts of citric and isocitric acids were produced. Cultivation of the mutant strain Y. lipolytica N 1 at pH 4.5 resulted in the predominant accumulation of citric acid (66.6 g/l) with an insignificant amount of isocitric acid. In the period of intense acid synthesis, high production of lipase was observed.     

Synthesis citric and isocitric acids by Yarrowia lipolytica during yeasts growth on rapeseed oils

The native strain Yarrowia lipolytica VKM Y-2373 grown in a complete medium exhibited the maximum lipase activity at the concentration of rapeseed oil of at least 5.0 g/l. In the course of yeast growth, no considerable changes were observed in the glycerol concentration, the proportions of the major free fatty acids formed via oil hydrolysis, or the fatty acid composition of oil. Under nitrogen limitation of cell growth, the accumulation of citric acids reached 77.1 g/l with predominance of isocitric acid at pH 6.0, whereas at pH 4.5, almost equal amounts of citric and isocitric acids were produced. Cultivation of the mutant strain Y. lipolytica N 1 at pH 4.5 resulted in the predominant accumulation of citric acid (66.6 g/l) with an insignificant amount of isocitric acid. In the period of intense acid synthesis, high production of lipase was observed.     

Ultrastructure of ependyma in brain third ventricle of the rats exposed to repeated tail-suspension. Scanning electron microscopical study

By means of scanning electron microscopy the ultrastructure of ependyma was studied in the brain third ventricle of the rats repeatedly exposed to 14-day tail-suspension (TS). Animals were subjected to TS for 30 days, then readapted to horizontal position during 30 days and again, repeatedly subjected to TS for 14 days simultaneously with the rats which were in TS for the first time during 14 days. Repeated TS of rats, inspite of repeated redistribution of body liquid mediums in cranial direction, results in considerably less expressed destructive changes in ultrastructure of ependymocyte cilia, then after primary 14- and 30-day TS, showing much greater cerebrospinal fluid (CSF) outflow from brain ventricles into sagittal venous sinus at postponed for a long time, repeated simulation of weightlessness effects in comparison with CSF outflow at primery one.