Selected contribution: Effects of aging on cerebrovascular tone and [Ca2+]i.

The lower limits of cerebral blood flow autoregulation shift toward high pressures in aged compared with young rats. Intraluminal pressure stimulates contractile mechanisms in cerebral arteries that might, in part, cause an age-dependent shift in autoregulation. The present project tested two hypotheses. First, cerebral artery tone is greater in isolated arteries from aged compared with mature adult rats. Second, aging decreases the modulatory effect of endothelium-derived nitric oxide (NO) and increases vascular smooth muscle Ca2+ sensitivity. Isolated segments of middle cerebral arteries from male 6-, 12-, 20-, and 24-mo-old Fischer 344 rats were cannulated and loaded with fura-2. Diameter and Ca2+ responses to increasing pressure were measured in HEPES, during NO synthase inhibition [NG-nitro-l-arginine methyl ester (l-NAME)], and after removal of the endothelium. Cerebral artery tone (with endothelium) increased with age. Only at the lowest pressure (20 and 40 mmHg) was intracellular Ca2+ concentration ([Ca2+]i) greater in arteries from 24-mo-old rats compared with the other age groups. l-NAME-sensitive constriction increased significantly in arteries from 6- to 20-mo-old rats but declined significantly thereafter in arteries from 24-mo-old rats. [Ca2+]i was less in arteries from 24-mo-old rats compared with the other groups after treatment with l-NAME. Another endothelial-derived factor, insensitive to l-NAME, also decreased significantly with age. For example, at 60 mmHg, the l-NAME-insensitive constriction decreased from 47 +/- 10, 42 +/- 5, 21 +/- 2, and 3 +/- 1 microm in 6-, 12-, 20-, and 24-mo-old rats, respectively. Our data suggest that aging alters cerebral artery tone and [Ca2+]i responses through endothelial-derived NO synthase-sensitive and -insensitive mechanisms. The combined effect of greater cerebral artery tone with less endothelium-dependent modulation may in part contribute to the age-dependent shift in cerebral blood flow autoregulation.     

Determination of nitrie in human blood by combination of a specific sample preparation with high-performance anion-exchange chromatography and electrochemical detection

All photometric or HPLC methods described to date have been unable to detect nitrite, a reliable marker of NO synthase activity, in human blood because of its rapid metabolism within the erythrocytes. We now elaborate on method to prevent nitrite degradation during sample preparation which in combination with high-performance anion-exchange chromatography and electrochemical detection allows a sensitive measurement of nitrite. A linear current response in the concentration range of 10–1000 nmol/l nitrite was observed yielding a correlation coefficient of 0.99. In addition, the combination of the electrochemical with a UV detector allowed us to simultaneously quantify nitrate one analytical run, which is the end product of NO/nitrite metabolism. Basal levels for nitrate and nitrite in human blood were determined with 25±4 μmol/l and 578±116 nmol/l (n=8), respectively and thus were in the same concentration range as expected from NO measurement in saline perfused isolated organs or cultured endothelial cells. Therefore, the presented method may be used to assess activity of endothelial constitutive NO synthase in humans under physiological and pathophysiological conditions.     

Characterization of a rice gene family encoding root-specific proteins

Two cDNA clones (RCc2 and RCc3) corresponding to mRNAs highly expressed only in root tissues of rice (Oryza sativa L.) seedlings were characterized. Respectively, they encode polypeptides of 146 (14.5 kDa) and 133 amino acids (13.4 kDa) that share high (<70%) sequence similarity with a polypeptide encoded by a cDNA (ZRP3) encoding an mRNA preferentially expressed in young maize roots. Genomic DNA blot analysis revealed that they are members of a small gene family and RCg2, the gene corresponding to RCc2, was isolated. A 1656 bp 5-upstream sequence of RCg2 was translationally fused to a -glucuronidase (GUS) reporter gene and stable introduction of the chimeric construct into rice was confirmed by PCR and genomic DNA blot analyses. Histochemical analysis of transgenic rice plants containing the full-length chimeric gene showed high levels of GUS activity in mature cells and the elongation and maturation zones of primary and secondary roots, and in the root caps, but no GUS activity was detected in root meristematic regions. Surprisingly, high GUS activity was also detected in leaves of the same plants. This raises the possibility that the RCg2 5-upstream element may not be sufficient for the proper spatial control of root specificity in transgenic rice.     

General relation between variance-time curve and power spectral density for point processes exhibiting 1/f β-fluctuations,with special reference to heart rate variability

Counting statistics in the form of the variance-time curve provides an alternative to spectral analysis for point processes exhibiting 1/f ^β-fluctuations, such as the heart beat. However, this is true only for β<1. Here, the case of general β is considered. To that end, the mathematical relation between the variance-time curve and power spectral density in the presence of 1/f ^β-noise is worked out in detail. A modified version of the variance-time curve is presented, which allows us to deal also with the case β?1. Some applications to the analysis of heart rate variability are given.     

Identification of Frankia Strains by Two-Dimensional Polyacrylamide Gel Electrophoresis

Fifteen Frankia strains from five different plant species were analyzed by two-dimensional polyacryl-amide gel electrophoresis to determine their relatedness by comparing the polypeptide patterns obtained. Three major subgroups (A, C, and D) were found in the Alnus-Comptonia-Myrica cross-inoculation group. An isolate from Purshia tridentata had a unique protein pattern and represents a distinct group of frankiae. Members of group A were isolated from root nodules of Alnus incana subsp. rugosa and Alnus viridis subsp. crispa. Group C organisms were from A. incana subsp. rugosa and Comptonia peregrina nodules, and group D organisms were from A. incana subsp. rugosa, A. viridis subsp. cripsa, and Myrica pensylvanica root nodules. Isolates from each gel group were obtained at several widely separated geographical locations. The results indicate that two-dimensional polyacrylamide gel electrophoresis is useful for identifying Frankia isolates.     

Substrate effects in tower loop reactors

Summary Hansenula polymorpha was cultivated in a bubble column loop bioreactor employing ethanol and/or glucose as substrates. By varying the substrate concentration, the cultivations were carried out in non-limited, substrate limited and oxygen transfer limited growth ranges. The influence of the transitions from one range to another on reactor performance (OTR,k _L a, a) and cell productivity () were investigated. When employing ethanol as a substrate, the concentration considerably influences the fluid dynamics, mass transfer phenomena and cell productivity. When employing glucose as a substrate, glucose repression occurs. At high glucose concentrations no transition into the oxygen transfer limited growth is possible. The ethanol produced during the glucose repression influences the fluid dynamics, mass transfer phenomena and productivity. With decreasing glucose concentration the glucose repression can be gradually eliminated.     

Process optimization of a continuous airlift tower-loop reactor

Based on the experimental investigations with H. polymorpha and Methylomonas M 15 in bench-scale airlift tower-loop reactors, a general distributed parameter model was developed and used to simulate to cultivation process in a 40-m-high production reactor. This general model was simplified with regard to the gas phase and loop balances and was employed to optimize cell productivity and/or profit in a 20-m-high pilot-plant airlift tower-loop reactor. Maximum cell productivity always occurs in the oxygen-transfer-limited growth range. In case of a high "penalty factor" for nonconsumed substrate, maximum profit is attained at the boundary between substrate and oxygen-transfer-limited growth. Oxygen-transfer limitation exists in the lower half of the tower, whereas in the upper half, substrate limitation prevails. The longitudinal dissolved oxygen concentration passes a minimum in this case as has been determined experimentally in the bench-scale column. The simulation results agree fairly well with the data measured in the pilot plant.     

Expression of the murine homologue of the cell cycle control protein p34cdc2 in T lymphocytes.

The mammalian homologue of the cdc2 gene of the fission yeast Schizosaccharomyces pombe encodes a p34cdc2 cyclin-dependent kinase that regulates the cell cycle of a wide variety of cell types. Resting murine T lymphocytes contained no detectable p34cdc2 protein, histone kinase activity, or specific mRNA for the cdc2 gene. Activation of the T cells by immobilized anti-CD3 resulted in the expression of specific mRNA late in the G1 phase of the cell cycle, and p34cdc2 protein was detectable at or near G1/S. At this point in the cell cycle, the protein was phosphorylated at tyrosine and displayed no H1 histone kinase activity. As the cells progressed through the cycle, the amount of specific mRNA and p34cdc2 increased, and H1 histone kinase activity was detectable when the cells were blocked at G2/M by nocodazole. The activation of T cells by phorbol dibutyrate induced the expression of IL-2R but failed to induce the synthesis of IL-2 or the expression of cdc2-specific mRNA. Under these conditions, the activated cells failed to enter the S phase of the cell cycle. Because the presence of IL-2 added exogenously during activation by phorbol dibutyrate resulted in the expression of cdc2-specific mRNA and progression through the cell cycle, either IL-2 or the interaction with IL-2R may be involved in the expression of cdc2 and regulation of the G1/S transition.     

The ultrastructural basis of steroid production in the Y-organ and the mandibular organ of the crabs Hemigrapsus nudus (Dana) and Carcinus maenas L.

Summary The ultrastructure of the steroid producing Y-organ and the mandibular organ of the crustaceans Hemigrapsus nudus and Carcinus maenas has been studied with reference to the well investigated steroid secreting cells (SSC) of mammals. In accordance with the most important characteristic of mammalian SSC, abundant SER could be shown in the Y-organ, where it is unevenly distributed. The amount of SER seems to vary in correlation with the secretion of moulting hormone during the moult cycle. Most Y-organ cells contain a great number of mitochondria of the tubular type, another important characteristic of mammalian SSC. The ultrastructure of the mandibular organ of C. maenas differs considerably from that of the Y-organ. Some SER was found, mitochondria of unusual shape and size were conspicuous. No definite conclusion as to the function of the mandibular organ is yet to be drawn.Dedicated to Prof. Dr. Peter Karlson on the occasion of his 60th birthdaySupported by the Deutsche Forschungsgemeinschaft, grant Ad 24/4We wish to thank Dr. A. Owczarzak, Oregon State University, Corvallis, Oregon, for providing the facilities for our work with H. nudus and Thomas Gallenstein for many helpful discussions of technical problems