Midsummer heat wave effects on lacustrine plankton: Variation of assemblage structure and fatty acid composition

The effects of the 2003 European heat wave on a freshwater plankton assemblage and its fatty acid (FA) composition were investigated. Composition and FA profiles of four size categories of planktonic organisms collected in 2003 were compared to those of the colder year 2002.     

Critical manifolds,travelling waves,and an example from population genetics

A generalized Morse index theory is used to study travelling waves in a natural selection-migration model for a diploid organism when the selective strength is weak.     

A hypothesis on p34cdc2 sequestration based on the existence of Ca(2+)-coordinated changes in H+ and MPF activities during Xenopus egg activation [corrected]

The entry into, and exit from, mitosis are controlled by a universal M-phase promoting factor (MPF) composed of at least p34cdc2 and a cyclin. Embryonic systems are convenient for studying the association and dissociation of the active MPF complex because oocytes and eggs are naturally arrested at a specific point of the cell cycle until progression to the next point is triggered by a hormonal signal or sperm. In amphibians, eggs prior to fertilization are arrested at metaphase 2 of meiosis due to the presence of a stabilized MPF complex. Fertilization (egg activation) produces a transient increase in intracellular free Ca2+, a propagating Ca2+ wave, that specifically triggers the destruction of cyclin, leading to MPF inactivation and entry into the first embryonic inter-phase. We have recently shown that intracellular pH (pHi) variations in amphibian eggs, a large increase at fertilization and small oscillations during the embryonic cell cycle, were temporally and functionally related to the corresponding changes in MPF activity. In addition, the recent finding that the pHi increase at fertilization in Xenopus eggs is a propagating, Ca(2+)-dependent pH wave which closely follows the Ca2+ wave, together with the absence in the egg plasma membrane of pHi-regulating systems responsible for that pHi increase, suggest the existence of cortical or subcortical vesicles acidifying in the wake of the Ca2+ wave, thus producing the pH wave.(ABSTRACT TRUNCATED AT 250 WORDS)     

Global bifurcations in the FitzHugh-Nagumo equations for nerve wave propagation

The FitzHugh-Nagumo equations for action potential propagation along nerve axons and the corresponding ordinary differential equations for travelling waves are solved numerically. Above a critical value, a constant bias current can drive a wave-front solution. At the critical value, a global bifurcation occurs. As a result, the wave front switches into a pulse.Based on a thesis by one of the authors (H. F.).     

Induction and ionic basis of slow wave potentials in seedlings of Pisum sativum L.

Slow wave potentials (SWPs) are transient depolarizations which propagate substantial distances from their point of origin. They were induced in the epidermal cells of pea epicotyls by injurious methods such as root excision and heat treatment, as well as by externally applied defined steps in xylem pressure (Px) in the absence of wounding. The common principle of induction was a rapid increase in Px. Such a stimulus appeared under natural conditions after (i) bending of the epicotyl, (ii) wounding of the epidermis, (iii) rewatering of dehydrated roots, and (iv) embolism. The induced depolarization was not associated with a change in cell input resistance. This result and the ineffectiveness of ion channel blockers point to H(+)-pumps rather than ion channels as the ionic basis of the SWP. Stimuli such as excision, heat treatment and pressure steps, which generate SWPs, caused a transient increase in the fluorescence intensity of epicotyls loaded with the pH-indicator DM-NERF, a 2',7'-dimethyl derivative of rhodol, but not of those loaded with the pH indicator 2',7'bis(2-carboxyethyl)-5-(and-6)-carboxyfluorescein (BCECF). Matching kinetics of depolarization and pH response identify a transient inactivation of proton pumps in the plasma membrane as the causal mechanism of the SWP. Feeding pump inhibitors to the cut surface of excised epicotyls failed to chemically simulate a SWP; cyanide, azide and 2,4-dinitrophenol caused sustained, local depolarizations which did not propagate. Of all tested substances, only sodium cholate caused a transient and propagating depolarization whose arrival in the growing region of the epicotyl coincided with a transient growth rate reduction.     

Metabolic compartmentation and substrate channelling in muscle cells

The published experimental data and existing concepts of cellular regulation of respiration are analyzed. Conventional, simplified considerations of regulatory mechanism by cytoplasmic ADP according to Michaelis-Menten kinetics or by derived parameters such as phosphate potential etc. do not explain relationships between oxygen consumption, workload and metabolic state of the cell. On the other hand, there are abundant data in literature showing microheterogeneity of cytoplasmic space in muscle cells, in particular with respect to ATP (and ADP) due to the structural organization of cell interior, existence of multienzyme complexes and structured water phase. Also very recent experimental data show that the intracellular diffusion of ADP is retarded in cardiomyocytes because of very low permeability of the mitochondrial outer membrane for adenine nucleotidesin vivo. Most probably, permeability of the outer mitochondrial membrane porin channels is controlled in the cellsin vivo by some intracellular factors which may be connected to cytoskeleton and lost during mitochondrial isolation. All these numerous data show convincingly that cellular metabolism cannot be understood if cell interior is considered as homogenous solution, and it is necessary to use the theories of organized metabolic systems and substrate-product channelling in multienzyme systems to understand metabolic regulation of respiration. One of these systems is the creatine kinase system, which channels high energy phosphates from mitochondria to sites of energy utilization. It is proposed that in muscle cells feed-back signal between contraction and mitochondrial respiration may be conducted by metabolic wave (propagation of oscillations of local concentration of ADP and creatine) through cytoplasmic equilibrium creatine and adenylate kinases and is amplified by coupled creatine kinase reaction in mitochondria. Mitochondrial creatine kinase has experimentally been shown to be a powerful amplifier of regulatory action of weak ADP fluxes due to its coupling to adenine nucleotide translocase. This phenomenon is also carefully analyzed.It is easier to explain biochemistry in terms of transport than it is to explain transport in terms of biochemistry. P. Mitchell The Ninth Sir Hans Krebs Lecture, Dresden, July 2, 1978.     

Monitoring global change with phenology: The case of the spring green wave

The centuries-old practice of recording plant and animal events that take place at specific times each year (phenology) should play an important role in monitoring mid-latitude global changes. At least three problems related to the detection of biosphere changes could be investigated using this information. Firstly, the technique can be generalized from the local to global scale. Secondly, an integrated approach could be developed to represent biome diversity effectively. Lastly, physical mechanisms responsible for the events can be deduced in order to incorporate the phenological information into global-scale models, and detect changes in related environmental factors. With these goals in mind, regional phenological data collection networks were initiated in eastern North America during the early 1960s, using cloned lilacs and several species of honeysuckle. This paper reviews research projects which address the problems outlined above, using first leaf data (associated with spring green-up or green wave in mid-latitudes) gathered from these networks. The results of such studies in North America have demonstrated the potential of phenology as an efficient monitor of global change throughout mid-latitude regions. Future research efforts will concentrate on the development of a coordinated strategy to link phenological information from satellites, indicator plants (such as the lilac), and representative species from each biome.     

体外冲击波碎石术对兔肝酶活性的影响

采用超微组织化学方法,观察了体外冲击波碎石术(ESWL)对家免肝脏酶活性的影响。实施 ESWL 后,肝细胞的琥珀酸脱氢酶(SDH)和毛细胆管壁上的碱性磷酸酶(ALP)、焦磷酸硫胺素酶(TPPase)反应活性减弱或消失。TPPase 从损伤的肝细胞高尔基体分泌面扁囊、溶酶体样小泡和毛细胆管内溢出,并伴有肝细胞面的质膜上出现了 TPPase 反应产物和形成膜包内凹小泡。结果提示 ESWL 可对肝细胞及毛细胆管的功能和结构有损伤作用。     

豚鼠耳蜗电图慢成分的研究

选用0.8-150Hz的带通滤波,从豚鼠圆窗记录出一负一正相慢电位.实验结果表明.其对0.5kHz短音的反应阈为729dB nHL.较耳蜗电图快成分低38.27dB nHL.通过离断听觉传导径路不同水平对该电位的观察,表明它是毛细胞及听神经电反应的慢成分.而且可能受听觉传出神经的调控.     

Spatial and temporal patterns of intracellular calcium in colonic smooth muscle

Summary Intracellular calcium [Ca²⁺] _i measurements in cell suspension of gastrointestinal myocytes have suggested a single [Ca²⁺] _i transient followed by a steady-state increase as the characteristic [Ca²⁺] _i response of these cells. In the present study, we used digital video imaging techniques in freshly dispersed myocytes from the rabbit colon, to characterize the spatiotemporal pattern of the [Ca²⁺] _i signal in single cells. The distribution of [Ca²⁺] _i in resting and stimulated cells was nonhomogeneous, with gradients of high [Ca²⁺] _i present in the subplasmalemmal space and in one cell pole. [Ca²⁺] _i gradients within these regions were not constant but showed temporal changes in the form of [Ca²⁺] _i oscillations and spatial changes in the form of [Ca²⁺] _i waves. [Ca²⁺] _i oscillations in unstimulated cells (n = 60) were independent of extracellular [Ca²⁺] and had a mean frequency of 12.6 +1.1 oscillations per min. The baseline [Ca²⁺], was 171 ± 13 nm and the mean oscillation amplitude was 194 ± 12 nm. Generation of [Ca²⁺] _i waves was also independent of influx of extracellular Ca²⁺. [Ca²⁺] _i waves originated in one cell pole and were visualized as propagation mostly along the subplasmalemmal space or occasionally throughout the cytoplasm. The mean velocity was 23 +3 m per sec (n = 6). Increases of [Ca²⁺] _i induced by different agonists were encoded into changes of baseline [Ca²⁺] _i and the amplitude of oscillations, but not into their frequency. The observed spatiotemporal pattern of [Ca²⁺] _i regulation may be the underlying mechanism for slow wave generation and propagation in this tissue. These findings are consistent with a [Ca²⁺] _i regulation whereby cell regulators modulate the spatiotemporal pattern of intracellularly generated [Ca²⁺] _i oscillations.The authors thank Debbie Anderson for excellent technical assistance with the electron microscopy and Dr. M. Regoli for providing the NK-1 agonist [Sar⁹,Met(O₂)¹¹]-SP. This work was supported by National Institutes of Health Grants DK 40919 and DK 40675 and Veterans Administration Grant SMI.