The action of glutamate and the problem op the “extracellular space” in the retina

Summary Turtle's retinae were incubated in isotonic Ringer and then studied with the electron microscope in order to determine if in these conditions an extracellular space appeared. In the incubated retinae, as in the normal ones no extracellular space was observed. The distance between adjacent membranes is of 120–250 Å and is filled with a cementing material.The Müller cell of the turtle's retina is described. The existence, at the choroidal end of this cell, of villous projections filled with vesicles and the accumulation of mitochondria under these projections would suggest that a process of micropinocytosis takes place in this site, and that it may be metabolically more active. After incubation, Müller cells showed no appreciable changes, in contrast with what happens to astrocytes in incubated slices of CNS (Gerschenfeld et al. 1959).The addition of sodium-l-glutamate to the incubation medium determined a marked swelling of the nervous endings in the inner synaptic layer and a similar though less pronounced change in the ganglion cells. This would indicate that the surcharge of water, sodium and chloride produced by glutamate (Ames 1956) is localized in this layer.The selective action of glutamate on the inner synaptic layer, in contrast with the excellent preservation of the outer synaptic layer, is probably linked to differences in biochemistry and physiology of synapses in these two strata.Work supported by a research grant from the Air Force Office of Scientific Research (5–60), U.S.A.     

Analysis and use of the perforated patch technique for recording ionic currents in pancreaticβ-cells

Summary To investigate the voltage dependence of the Na^–/K^– pump, current-voltage relations were determined in prophasearrested oocytes ofXenopus laevis. All solutions contained 5mm Ba^2– and 20mm tetraethylammonium (TEA) to block K^– channels. If. in addition, the Na⁺/K⁺ pump is blocked by ouabain, K⁺-sensitive currents no larger than 50 nA/cm² remain. Reductions in steady-state current (on the order of 700 nA/cm²) produced by 50 m ouabain or dihydro-ouabain or by K⁺ removal, therefore, primarily represent current generated by the Na^–/K^– pump. In Na^–-free solution containing 5mm K⁺, Na⁺/K⁺ pump current is relatively voltage independent over the potential range from –160 to +40 mV. If external [K⁺] is reduced below 0.5mm, negative slopes are observed over this entire voltage range. Similar results are seen in Na⁺- and Ca²⁺-free solutions in the presence of 2mm Ni²⁺, an experimental condition designed to prevent Na⁺/Ca²⁺ exchange. The occurrence of a negative slope can be explained by the voltage dependence of the apparent affinity for activation of the Na⁺/K⁺ pump by external K⁺, consistent with the existence of an external ion well for K^– binding. In 90mm Na⁺, 5mm K⁺ solution, Na⁺/K⁺ pump current-voltage curves at negative membrane potentials have a positive slope and can be described by a monotonically increasing sigmoidal function. At an extracellular [K⁺] of 1.3mm, a negative slope was observed at positive potentials. These findings suggest that in addition to a voltage-dependent step associated with Na⁺ translocation, a second voltage-dependent step that is dependent on external [K⁺], possibly external K⁺ binding, participates in the overall reaction mechanism of the Na⁺/K⁺ pump.     

Some theoretical aspects of protein coevolution in the ecosystem “phage-bacteria” I. The problem

The possibility of prolonged coevolution of bacterial reception protein and viral adsorption one is questioned in this paper. A general deterministic model of ecosystem “phage-bacteria” is formulated. Analysis of the model accentuates the problem of clearing up conditions that provide steady regimes not of coexistence but coevolution, i.e. successive mutational changes of mutually “coadaptive” pairs of mutant strains of bacteria and phages. Heuristic validity of this model in a framework of some actual problems and paradoxes of molecular evolution theory is particularly emphasized.     

Nitrogen stress in wheat — Its measurement and relation to leaf nitrogen

Summary The intensity of nitrogen deficiency in the young wheat plant was measured over a range of 1 to 83 per cent of nitrogen stress. Within these limits of tress relative growth rate of tops fell from 11 to 2 per cent per day.Symptoms of nitrogen deficiency appeared when the stress was greater than 40 per cent.Nitrogen stress in the variety Gabo is calibrated in terms of the concentrations of total nitrogen, soluble nitrogen and free ninhydrin nitrogen of the youngest fully expanded leaf.     

Contributions to the mathematical theory of epidemics—II. The problem of endemicity

(1) A mathematical investigation has been made of the prevalence of a disease in a population from which certain individuals are being removed as the result of the disease, whilst fresh individuals are being introduced as the result of birth or immigration. Allowance is made for the effects of the immunity produced as the result of an attack of the disease, but the effect of deaths from other causes is not taken into account, and the action of the disease is supposed to be independent of the age of the individual. (2) As a special case of the above, results have been obtained for a closed population in which no deaths occur and to which no fresh individuals are added, but in which the individuals after being infected acquire immunity, and then may be again infected. A threshold density of population exists analogous to that described in the previous paper, which is such that no disease can exist in a population, the density of which is below the threshold. (3) In other special cases investigated when either immigration or birth is operative in the supply of fresh individuals, as well as in the general case, only one steady state of disease is possible. To reach this state the population must be of a certain density which will be determined by the functions characterizing the infectivity, morbidity, etc., of the disease. (4) Increase of the immigration rate or of the birth-rate results in an increase in the rate of infection of the healthy individuals and also in the percentage rate of infection, the percentage of sick, and in the percentage of mortality from the disease. This result is, of course, a necessary consequence of our assumption that the disease is the only cause of death. (5) More particular results have been obtained by substituting constants in the place of the undetermined functions assumed in the general theory. Further, under these conditions the nature of the steady states has been more fully investigated and it has been shown that in all cases, except one, the steady states are stable ones. In the exception, a disturbance would result in purely periodic oscillations about the steady state.     

Water relation parameters of the CAM plant Kalanchoë daigremontiana in relation to diurnal malate oscillations

Summary In the CAM plant Kalanchoë daigremontiana, kept in an environmental rhythm of 12 h L: 12 h D in a growth chamber at 60% relative humidity and well watered in the root medium, decreasing water potentials and osmotic potentials of the leaves are correlated with malate accumulation in the dark. In the light increasing water and osmotic potentials ( _W and _S ) are associated with decreasing malate levels. Transpiratory H₂O loss is high in dark and low in light.In continuous light, the CAM rhythm rapidly disappears in the form of a highly damped endogenous oscillation. Malate levels, and water and osmotic potentials of the leaves remain correlated as described above. However, transpiration is very high as malate levels decrease and water and osmotic potentials increase.It can concluded, that water relation parameters like total water potential ( _W ) and osmotic potential ( _S ) change in close correlation with changes of malic acid levels. As an important osmotically active solute in CAM plants, malic acid appears to affect water relations independently of and in addition to transpiration. The question remains open, whether turgor ( _P ) is involved in CAM regulation in intact plants in a similar way as it determines malate fluxes in leaf slices.Abbreviations CAM Crassulacean Acid Metabolism - L Light - D Dark     

Thiamine requirement in relation to cytokinin in “normal” and “mutant” strains of tobacco callus

Summary High concentrations of kinetin (400–2,000 g/l) permit continuous growth of tobacco callus cultures (Nicotiana tabacum, var. Wisconsin No. 38) in the absence of exogenous thiamine. On the optimum concentration (1,000 g/l) the tissue has been maintained through 21 bimonthly passages without change in vigor or other growth characteristics.The effect of kinetin is general, not mutagenic, because tissue returned to low-kinetin, thiamine-free medium failed to grow.Kinetin-thiamine interactions in cytokinin mutant strains which were grown without cytokinin in light and darkness suggest that the endogenous content of cytokinins may markedly affect the requirement for thiamine and possibly the tissue content of this vitamin and other growth factors.The viability of tissue on low-kinetin media in enhanced by thiamine, but the addition of this vitamin does not eliminate the requirement for a cytokinin.The great divergence in minimum kinetin concentrations required for growth of the tissue in the presence and absence of thiamine indicates that the growth promoting action of cytokinin must be different in the two cases.     

The relation of the adenosine 5′-triphosphate-adenosine 5′-diphosphate exchange activity to photophosphorylation in swiss-chard chloroplasts

The presence of an enzyme-catalyzing ATP-ADP exchange in unwashed chloroplasts was confirmed. Chloroplast fragments from swiss-chard possessed little to no ATP-ADP exchange activity while maintaining most of the photophosphorylative activity of unwashed chloroplasts. The ATP-ADP exchange activity was completely recovered in the supernatants collected during the preparation of chloroplast fragments from unwashed chloroplasts. Consequently, it is suggested that the ATP-ADP exchange enzyme is not a constituent of the photophosphorylative machinery.A strong correlation was found between the exchange activity and ATP: 3-phosphoglycerate transphosphorylative activity during the purification of the exchange enzyme from swiss-chard or spinach chloroplasts.Commercial crystalline yeast phosphoglycerate kinase (ATP: 3-phospho-D-glycerate I-phosphotransferase, EC 2.7.2.3) catalyzed an ATP-ADP exchange reaction. GDP inhibited to a similar extent the transphosphorylation and ATP-ADP exchange activities of the crystalline yeast phosphoglycerate kinase. The possibility that the exchange activity found in chloroplasts may be related to phosphoglycerate kinase is discussed.     

A critical review of the ‘neugliederung’ concept in relation to the development of the vertebral column

Summary The literature on the early embryonic development of the vertebral column in various animal species was analyzed to evaluate so many unrelated or contradictory observations. The recurring problems are described. One of the first was the lack of correspondence between the metameric boundaries of the primitive vertebral bodies arising from the somites and those of the adult vertebral bodies, as presumably shown by their relationship to the vertebral processes and spinal nerves. A century ago, Remak introduced the concept of Neugliederung, according to which the ultimate vertebral body boundaries are determined by a shift of a half segment in comparison with the earlier segment boundaries.     

The short—term variation of asthma in Brisbane: Its relation to the weather and other factors

In the cooler portions of the six years 1961–1966, there were 22 weeks in which the night attendances for asthma at the Royal Brisbane Hospital Casualty Department were much higher than would be expected from the seasonal and annual variation, 23 weeks in which they were much lower, and 114 intermediate weeks. The high-asthma weeks differed significantly from intermediate weeks in having on the average a greater decrease from the previous week in mean and minimum temperature, dew point, relative humidity and rainfall, and a greater increase in hours of sunshine. There was a significant association with the arrival of a cold dry change. No significant difference was found with smoke density, fungal elements or pollens. In many of the individual high-asthma weeks the increase in asthma occurred within 48 hours after a definite fall in minimum temperature or dew point or both. However, in some of the weeks, particularly in spring, there had not been a cold or dry change, and many cold dry changes were not followed by an increase in asthma. The low-asthma weeks differed significantly from intermediate weeks in having on the average a higher dew point and relative humidity, more rainy days, a lower temperature range and fewer hours of sunshine. This applied particularly to autumn. In autumn and spring, rain was significantly less frequent on days with asthma attendances than on days with none. These relationships are largely the converse of those with high-asthma weeks.

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Zusammenfassung Während der kühleren Jahreszeiten in 6 Jahren (1961–1966) waren 22 Wochen in denen die Anzahl der nächtlichen Einlieferungen wegen Asthma im Royal Brisbane Hospital weit höher war als die erwartete Anzahl, 23 Wochen in denen sie wesentlich geringer war, und 114 Wochen mit einer mittleren Anzahl Fälle. Die Wetterbedingungen während der Wochen mit vielen Asthmafällen waren signifikant unterschieden von denen mit mittlerer Häufigkeit. Im Mittel waren die mittlere und die Minimaltemperatur tiefer als in der vorausgegangenen Woche, es waren weniger Regen, niedrigere Luftfeuchtigkeit und mehr Stunden Sonnenschein. Es bestand eine signifikante Beziehung zu dem Eintreffen kalter trockener Luft. Dagegen bestand keine Beziehung zur Dichte der Luftverunreinigung und der Menge Pilzsporen und Pollen in der Luft. In vielen Wochen trat Asthma innerhalb 48 Stunden nach dem Fall der Temperatur und Feuchtigkeit auf. Während einiger Wochen dagegen, besonders im Frühling, lag dieser Wetterwechsel nicht vor und in vielen Fällen bewirkte der Wechsel keinen Anstieg der Asthmahäufigkeit. Während der Wochen mit niedriger Asthmahäufigkeit waren im Mittel die Feuchtigkeit erhöht, ein geringerer Temperaturwechsel, weniger Regen und weniger Sonnenscheinstunden, besonders im Herbst. Im Herbst und Frühling war signifikant weniger Regen an Tagen mit als an Tagen ohne Asthmameldungen. Diese Beziehungen waren weitgehend umgekehrt von denen in Wochen mit hoher Asthmahäufigkeit.

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Resume Des statistiques de la permanence du \"Royal Brisbane Hospital\" il appert que durant les périodes froides des années 1961 à 1966, on a dénombré 22 semaines pendant lesquelles, la nuit, les entrées d'urgence causées par des crises d'asthme furent beaucoup plus nombreuses que ne le laissaient supposer les variations saisonnières et annuelles. Durant les mêmes laps de temps, on en a décompté 23 pendant lesquelles les crises nocturnes d'asthme étaient moins fréquentes et 114 qui occupent une position intermédiaire. Les semaines à haute fréquence d'asthme présentent des moyennes de température, des minimums journaliers, des points de rosée, des humidités relatives et des précipitations inférieurs et une durée d'insolation supérieure à la normale et cela de façon significative. On a pu déceler une relation significative entre les crises d'asthme et des invasions d'air froid et sec. On n'a par contre pas pu déceler de différences en ce qui concerne le taux de fumée ou le nombre de spores et de grains de pollen. Dans bon nombre de semaines avec de hautes fréquences d'asthme, le déclenchement des crises se produit 48 heures après la chute du minimum de la température ou du point de rosee, voire des 2 ensemble. Pourtant, quelques unes de ces semaines — au printemps surtout — n'ont pas connu d'invasion d'air froid et sec et de nombreuses invasions de ce type ne furent pas suivies d'une augmentation du nombre de crises. Les semaines de faible fréquence se distinguent de façon significative de la classe intermédiaire en ce sens qu'elles présentent en moyenne des points de rosée et une humidité plus élevés, plus de jours avec précipitations, une température plus basse et moins d'heures d'insolation. Ceci est valable surtout en automne. En automne et au printemps, la pluie fut moins fréquente les jours où l'on note des crises d'asthme qu'à ceux où il n'y en a pas. Cette relation est en général inverse à celle que l'on rencontre durant les semaines à haute fréquence de crises d'asthme.

     

The ultrastructure of the “difference factor” in the myelin

Summary Electron-microscopic studies of peripheral nerves as prepared by the freezeetching method show the myelin lamella to be 185 Å thick. This is the same dimension found by x-ray diffraction analysis of natural myelin. In contrast to the appearance of osmiumfixed material, the cytoplasmic surfaces of the paired membranes in the myelin lamella are apposed to two fine, separate lines, while the outer membrane sides are fused into a broader single line. The finding of a decidedly different structure for the outer and for the inner membrane surfaces appears to be the cause of the difference factor.This work was supported by the Swiss National Foundation (Nr. 4065). — Acknowledgement: We thank the Balzers AG. (9496 Balzers, Fürstentum Liechtenstein) for providing us with the High Vakuum Device.