Showing papers by "University of Seville published in 1988"

Chemotransduction in the carotid body: K+ current modulated by PO2 in type I chemoreceptor cells.

Abstract: The ionic currents of carotid body type I cells and their possible involvement in the detection of oxygen tension (Po2) in arterial blood are unknown. The electrical properties of these cells were studied with the whole-cell patch clamp technique, and the hypothesis that ionic conductances can be altered by changes in PO2 was tested. The results show that type I cells have voltage-dependent sodium, calcium, and potassium channels. Sodium and calcium currents were unaffected by a decrease in PO2 from 150 to 10 millimeters of mercury, whereas, with the same experimental protocol, potassium currents were reversibly reduced by 25 to 50 percent. The effect of hypoxia was independent of internal adenosine triphosphate and calcium. Thus, ionic conductances, and particularly the O2-sensitive potassium current, play a key role in the transduction mechanism of arterial chemoreceptors.

Short and long fatigue crack growth: A unified model

Abstract: In this model the growth of a crack is analysed in terms of the successive blocking of the plastic zone by slip barriers (e.g. grain boundaries) and the subsequent initiation of the slip in the next grain. The discontinuous character of the slip process (slip jumps) plays a fundamental role in the model. The factor governing the transfer of slip across a grain boundary is considered to be the stress concentration ahead of the plastic zone which, for a constant applied stress τ, is found to be dependent only on a parameter n = a/c defining the position of the crack tip relative to the grain boundary. The discrete behaviour of the slip has a strong influence in the short-crack period and hence cannot be neglected in the analysis of the crack growth rate. This period is characterized by large variations in the parameter n. In the long-crack period the slip jumps do not influence the overall description of the growth and the parameter n is almost constant. By making the crack extension per cycle prop...

A microstructurally-short fatigue crack growth equation

Abstract: — A brief outline of a recently developed model which describes the microstructurally short and the physically short crack periods of fatigue crack growth is presented. A single equation to describe both regimes is discussed and the model applied to data on a medium carbon steel. Good predictions relating to the actual experimental lifetime were achieved. The results are compared with the prediction of fatigue life based on a previously reported two-equation approach.

Melanin production by Rhizobium strains.

Abstract: Different Rhizobium and Bradyrhizobium strains were screened for their ability to produce melanin. Pigment producers (Mel + ) were found among strains of R. leguminosarum biovars viceae, trifolii , and phaseoli, R. meliloti , and R. fredii ; none of 19 Bradyrhizobium strains examined gave a positive response. Melanin production and nod genes were plasmid borne in R. leguminosarum biovar trifolii RS24. In R. leguminosarum biovar phaseoli CFN42 and R. meliloti GR015, mel genes were located in the respective symbiotic plasmids. In R. fredii USDA 205, melanin production correlated with the presence of its smallest indigenous plasmid. Images

Long-term vegetation changes on the stabilized dunes of Doñana National Park (SW Spain)

Abstract: Changes in the vegetation of stabilized sand dunes of Donana National Park in the last four centuries have been analysed, combining ecological and historical sources of information. Quantitative vegetation data have been obtained from 5 inventories of a 15 km long transect, consisting of 34 points where nearby woody plants have been recorded. Inventories were taken in 1636, 1647, 1652, 1682 and 1859. The analysis of these data, combined with climatic and management information on the area, reveals that until 1636 a mediterranean forest dominated byQuercus suber, existed; it was used as a game preserve. From 1636 to 1682 vegetation underwent profound changes with a marked drop in trees and mature scrub. The vegetation was replaced by a pioneer scrub species. This rapid change was brought about by the introduction of cattle and pigs, timber and cork exploitation, and the use of prescribed fire. The climatic crisis that arose circa 1700 led to erosion of the sandy soils, which made the vegetation change irreversibly. Livestock pressure hampered natural forest regeneration until 1737 whenPinus pinea plantations started. From then onwards little change in vegetation is known to have occurred. It is suggested that the main steps of change in Donana vegetation history may have occurred in many other areas of the Mediterranean Basin.

Yeast cell viability under conditions of high temperature and ethanol concentrations depends on the mitochondrial genome.

Abstract: Wine yeasts manifest simultaneously a high tolerance to ethanol, thermotolerance, and a high resistance to the mutagenic effects of ethanol on the mitochondrial genome. The transfer of mitochondria from these strains to laboratory yeasts demonstrate that this genome influences the above parameters, since thermotolerance, ethanol-growth tolerance, and the frequency of rho- mutants were either totally or partially modified in the laboratory recipient strain. When the death rate and the rate of formation of rho- mutants were measured under extreme conditions of inhibitory ethanol concentrations and high temperature, a perfect correlation was found between these parameters, and both of them were dependent on the strain of mitochondrial genome. Thus, the transfer of wine yeast mitochondria leads to a lower death rate, and a simultaneous increase in thermotolerance and ethanol tolerance in the recipient strain. These results demonstrate the role that viability plays under conditions of high temperatures and high ethanol concentrations. The greater stability of the rho+ phenotype shown by the wine yeast mitochondrial genome may be responsible for the increased viability conferred by these mitochondria.

Mode ordering algorithms for sparse vector method improvement

Abstract: Three node-ordering algorithms that enhance sparse vector methods without losing sparse matrix method efficiency are presented. The performance of the algorithms is compared with that of the minimum-degree algorithm for eight test systems up to 661 nodes. For the factorization of a sparse matrix into U/sup t/U, the new algorithms give a similar or even better sparsity for U, while clearly improving the sparsity of U/sup -1/. >

Ionic basis of the differential neuronal activity of guinea-pig septal nucleus studied in vitro.

Abstract: 1. The electrical properties and ionic conductances of septal neurones were studied by intracellular recording in an in vitro slice preparation. Within the total number of cells recorded (n = 150) we identified three electrophysiological cell types, each one of them located in a separate septal region. Dorsolateral septal neurones comprised 60% of the cells, intermediate septal neurons 10%, and medical septal neurones 30%. 2. Passive electrical constants of dorsolateral, intermediate and medial septal neurones were, respectively:resting potential (-60.2 +/- 4.8, -59.8 +/- 3.3 and -56 +/- 4.3 mV); input resistance (82.5 +/- 17, 63 +/- 16 and 83 +/- 18 M omega) and membrane time constant (18.5 +/- 7.3, 14.2 +/- 6.8 and 10.7 +/- 3.4 ms). 3. Direct activation of dorsolateral septal neurones by current injection below 0.2 nA triggered repetitive firing of fast action potentials. Larger current pulses elicited a characteristic response consisting of an initial fast action potential followed by a train of slow spikes. An after-hyperpolarization followed termination of the pulse and the characteristic response. 4. In dorsolateral septal neurons tetrodotoxin (TTX) abolished the fast action potentials. The slow spikes and the after-hyperpolarization disappeared in presence of Co2+ or after brief removal of external Ca2+. This suggests that the characteristic response is mediated by Ca2+ and the after-hyperpolarization by a Ca2+-dependent K+ conductance. 5. The firing pattern of intermediate septal neurones activated from the resting potential spontaneously measured in the cells was similar to that of dorsolateral septal neurones; but direct activation from a hyperpolarized membrane potential evoked in intermediate septal cells a bursting response due to the generation of a low-threshold spike. The low-threshold spike was TTX-resistant but abolished by Co2+ and reached a maximal amplitude after hyperpolarization to -75 mV lasting for 100-150 ms. These results suggest the existence in intermediate septal neurons of a low-threshold Ca2+ conductance inactivated at the resting potential and deinactivated by hyperpolarization. 6. Depolarization of medial septal neurons by current pulses of amplitude greater than 0.2-0.3 nA elicited a typical burst of two to six action potentials. The bursts lasted for 20-50 ms and were followed by a marked after-hyperpolarization.(ABSTRACT TRUNCATED AT 400 WORDS)

Growth kinetics of the Golgi apparatus during the cell cycle in onion root meristems.

Abstract: In onion root meristems, the number of dictyosomes per cell shows a kinetics of growth strongly related to the cell cycle. During the interphase of steady-state proliferative cells, the volume density and numerical density of the Golgi apparatus decrease to reach minimum values in late-interphase cells, characterized by their greatest length. This pattern is also found in the total volume occupied by Golgi apparatus. Once in mitosis, the above-mentioned parameters begin to increase reaching maximum mean values in telophase. After the experimental uncoupling of chromosome and growth cycles by presynchronization with hydroxyurea, we found a similar behaviour pattern in the Golgi apparatus: decreasing values during interphase and a triggering of Golgi-apparatus growth in prophase independently of the bigger cell sizes reached in mitosis as an effect of pretreatment with hydroxyurea. These results indicate a cyclic kinetics of this subcellular component in higher-plant meristems, coupled with early mitotic events.

Exotic radioactivity as a superfluid tunneling phenomenon.

Abstract: The recently discovered radioactive decay of heavy nuclei by emission of carbon and neon is described by a model containing elements from both the theory of \ensuremath{\alpha} decay and that of fission. A key ingredient is the inertial mass, which depends on the superfluid pairing gap of the nucleus. The potential energy is estimated from macroscopic considerations. Theory and experiment fit together in a reasonable way to give an overall picture of exotic decay.

Induction of petite yeast mutants by membrane-active agents

Abstract: Ethanol proved to be a strong mutagenic agent of Saccharomyces mitochondrial DNA. Other active membrane solvents, such as tert-butanol, isopropanol, and sodium dodecyl sulfate, also turned out to be powerful petite mutation [rho-] inducers. Mutants defective in ergosterol synthesis (erg mutants) showed an extremely high frequency of spontaneous petite cells, suggesting that mitochondrial membrane alterations that were caused either by changes in its composition, as in the erg mutants, or by the effects of organic solvents resulted in an increase in the proportion of petite mutants. Wine yeast strains were generally more tolerant to the mutagenic effects of alcohols on mitochondrial DNA and more sensitive to the effect of sodium dodecyl sulfate than laboratory strains. However, resistance to petite mutation formation in laboratory strains was increased by mitochondrial transfer from alcohol-tolerant wine yeasts. Hence, the stability of the [rho+] mitochondrial DNA in either the presence or absence of solvents depends in part on the nature of the mitochondrial DNA itself. The low frequency of petite mutants found in wine yeast-laboratory yeast hybrids and the fact that the high frequency of petite mutants of a particular wine spore segregated meiotically indicated that many nuclear genes also play an important role in the mitochondrial genome in both the presence and absence of membrane solvents.

The transition from nonadiabatic to solvent controlled adiabatic electron transfer kinetics: The role of quantum and solvent dynamics

Abstract: We analyze the transition from nonadiabatic to solvent controlled adiabatic electron transfer kinetic behavior with emphasis on the inverted regime. By viewing the electron transfer process as dynamical motion on a donor surface followed by possible crossing to the acceptor surface, we are able to obtain a simple consecutive reaction expression for the overall rate in terms of rate constants for motion on the surfaces and crossing motion. When the crossing between surfaces is not localized to a point, we find that there are frictional effects on this crossing rate constant, in contrast to the localized case. Use of typical electron transfer parameters shows that these friction effects will only be in evidence for the inverted regime of electron transfer kinetics.

End-product regulation of carotenogenesis in Phycomyces

Abstract: Wild-type Phycomyces blakesleeanus synthesizes the yellow pigment, beta-carotene. Colour mutants exhibit various alterations in the biosynthesis of beta-carotene or in its regulation. The presence of certain chemicals in the medium stimulates carotenogenesis in the wild type. We attribute different mechanisms of action to agents which stimulate or fail to stimulate different sets of mutants; this is the case of retinol and dimethyl phthalate. Dimethyl phthalate and veratrol are active on the same mutants, and therefore are likely to act in the same way. The main regulation of carotenogenesis, end-product inhibition, does not operate in the mutants of certain genes; these mutants are indifferent to retinol. By using a collection of retinoids we conclude that their action depends on their structural similarity to a part of the beta-carotene molecule. From these and other observations we propose that end-product inhibition of the pathway is mediated by a complex of beta-carotene and two gene products and that the retinoids compete with beta-carotene and prevent end-product inhibition.

Selection of Ethanol-Tolerant Yeast Hybrids in pH-Regulated Continuous Culture.

Abstract: Hybrids between naturally occurring wine yeast strains and laboratory strains were formed as a method of increasing genetic variability to improve the ethanol tolerance of yeast strains. The hybrids were subjected to competition experiments under continuous culture controlled by pH with increasing ethanol concentrations over a wide range to select the fastest-growing strain at any concentration of ethanol. The continuous culture system was obtained by controlling the dilution rate of a chemostat connected to a pH-meter. The nutrient pump of the chemostat was switched on and off in response to the pH of the culture, which was thereby kept near a critical value (pHc). Under these conditions, when the medium was supplemented with ethanol, the ethanol concentration of the culture increased with each pulse of dilution. A hybrid strain was selected by this procedure that was more tolerant than any of the highly ethanol-tolerant wine yeast strains at any concentration of ethanol and was able to grow at up to 16% (vol/vol) ethanol. This improvement in ethanol tolerance led to an increase in both the ethanol production rate and the total amount of ethanol produced.

The importance of metallic elements in wine. A literature survey.

Abstract: A review of the current literature concerning the role played by metallic elements present in wine is presented. The aim is to show the importance of these elements in the entire wine-making process, mainly through their influence on the organoleptic properties of wine. The study takes into consideration the individual stages of the process such as fertilization, fermentation and aging and also deals with other interesting aspects related to hygiene and dietetic properties, as well as the possibility of differentiating wines according to their metal contents.

Photomorphogenesis inPhycomyces: Fluence-response curves and action spectra.

Abstract: Blue light regulates vegetative reproduction inPhycomyces blakesleeanus Bgff. by inhibiting the development of microphores and stimulating that of macrophores. Fluence-response curves were obtained at twelve different wavelengths. Each response exhibits a two-step (“biphasic”) dependence on fluence, as if it resulted from the addition of two separate components with different thresholds, midpoints, and amplitudes. The absolute threshold is close to 10 photons·μm2. The threshold fluence of the low-intensity component is about 104 times smaller than that of the high-intensity component. The action spectra for each of the two components of the two responses share general similarities, but exhibit significant differences that might be taken to favour four separate photosystems. Additional complexity is indicated by the wavelength dependence of the saturation levels.

Fine needle aspiration cytology of paraganglionic tumors

Abstract: A comparative study of six paragangliomas from different locations and with different clinical behavior was performed. The fine needle aspirates in all cases were similar: abundant cells with round or oval nuclei and marked anisokaryosis with a tendency to form acini or follicular structures. Pheochromocytomas often contained binucleated cells and had cells with prominent intranuclear cytoplasmic inclusions more often than did other paraganglionic tumors. Similar features were seen in the excised tumors. Evaluation of the significance of nuclear variations with morphometry confirmed the subjective impression that nuclear pleomorphism is not an indicator of the biologic behavior of these lesions; paradoxically, malignant paragangliomas show less anisokaryosis than do their benign counterparts.

Theoretical calculations of proton affinities of azines. Prediction of the relative basicities and preferred protonation sites

Abstract: Theoretical calculations at the 3‐21G and 3‐21 + G ab initio levels and at the MNDO and AM1 semiempirical levels of several six‐membered nitrogenated heterocycles and their protonated species have been carried out. The 3–21G calculated proton affinities are systematically too high, in relation to the available experimental data, and it is estimated that inclusion of electron correlation and zero‐point corrections is not sufficient to reach the desired agreement; however, additional inclusion of diffuse functions (3‐21 + G/3‐21G calculations) lowers the calculated proton affinities by 5.4–6.8 kcal/mol, a good agreement being thus obtained, at least for 1–7. On the other hand, semiempirical methods underestimate the repulsion between each pair of vicinal nitrogens; however, if a correction of ˜9 kcal/mol is added to the AM1 results for each pair of neighboring nitrogens containing lone pairs of electrons, the corresponding proton affinities match fairly well the available exoerimental data and corrected 3‐21 + G results. As expected, all methods predict that the introduction of additional nitrogens decreases the overall absolute basicity. Futhermore, comparison of the relative basicity of the isomers and of the preferred protonation site for each isomer indicates that nitrogen atoms with (only) one α‐nitrogen and without a γ‐nitrogen are more basic than any others. In benzazines, MNDO and AM1 suggest that the 2,3‐diaza arrangement has a higher intrinsic basicity than the 1,2‐diaza arrangement.

Offense and Defense after Lateral Septal Lesions in Columba Livia

Abstract: It is generally agreed that there are several different types of animal aggression that may be distinguished in terms of their neural organization and that discrete lesions, in particular brain areas, may affect one but not other types of aggression. In this study the effects of electrolytic, bilateral lesions in lateral septum on offense and defense were examined in pigeons. Subjects were tested by introducing an adult conspecific stranger into their home cage. A postoperative increase in offensive patterns and a long-lasting drop in defense were observed in the lesioned birds. Its remarkable resemblance to the effects of antianxiety drugs, as well as the difference between the behavioral effects of medial septal damage are also discussed.

Discrimination of the kinetic model of overlapping solid-state reactions from non-isothermal data

Abstract: A method has been developed that allows the deconvolution of up to 15 overlapping solidstate reactions without previous assumptions. Both the kinetic parameters and the reaction mechanisms fitted by the unit reactions can be determined from a series of non-isothermal experiments carried out at different heating rates.