Alpine species seed longevity in the soil in relation to seed size and shape – A 5-year burial experiment in the Central Alps

Long-term persistent seeds are generally expected to be small and spherically shaped. In contrast, transient seeds are often large, flattened and elongated. We hypothesized that alpine species follow these trends, and that most species of unstable alpine habitats have the potential to form long-term persistent seed banks. The latter would enable them to delay germination until favourable conditions are present in their environment thereby increasing the likelihood for establishment of seedlings. We selected nine alpine species of more or less unstable habitats (i.e. Achillea moschata, Artemisia genipi, Anthyllis vulneraria ssp. alpicola, Geum reptans, Linaria alpina, Oxyria digyna, Saxifraga aizoides, Saxifraga oppositifolia, and Trifolium pallescens) for this study. Seed longevity was estimated by a 5-year burial experiment in the field with seed excavations after 1 winter, 2 years and 5 years. Germination experiments in the growth chamber and viability tests were performed after each excavation. We detected longevity patterns ranging from transient to long-term persistent. Two species were classified as transient. All other species have the potential to form persistent seed banks, with almost half of the investigated species showing a trend for long-term persistence. Despite contradictory reports, long-term persistent seed banks are an important life history trait of species of unstable alpine habitats. We found that seed shape and hard-seededness are good predictors of seed persistence of alpine species. Seed size seems to be less important. The data from this study support the general hypotheses describing the relationship among seed size, seed shape and seed persistence in the soil.     

Two Kinds of Transient Outward Currents, I A and I Adepol , in F76 and D1 Soma Membranes of the Subesophageal Ganglia of Helix aspersa

Transient outward currents were characterized with twin electrode voltage clamp techniques in isolated F76 and D1 neuronal membranes (soma only) of Helix aspersa subesophageal ganglia. In this study, in addition to the transient outward current (A-current, I _A ) described by Connor and Stevens (1971b), another fast outward current, referred to as I _Adepol here, is described for the first time. This is similar to the current component characterized in Aplysia (Furukawa, Kandel & Pfaffinger, 1992). The separation of these two current components was based on activation and steady-state inactivation curves, holding potentials and sensitivity to 4-aminopyridine (4-AP). In contrast to I _A , I _Adepol did not require hyperpolarizing conditioning pulses to remove inactivation; it was evoked from a holding potential of −40 mV, at which I _A is completely inactivated. I _Adepol shows noticeable activation at around −5 mV, whereas I _A activates at around −50 mV. The time courses of I _Adepol activation and inactivation were similar but slower than I _A . It was found that I _Adepol was more sensitive than I _A to 4-AP. 4-AP at a concentration of 1 mm blocked I _Adepol completely, whereas 5–6 mm 4-AP was needed to block I _A completely. This current is potentially very important because it may, like other A currents, regulate firing frequency but notably, it does not require a period of hyperpolarization to be active. Received: 12 May 2000/Revised: 12 October 2000     

大鼠肢体预缺血减小心肌缺血-再灌注后的梗塞范围

在氨基甲酸乙酯麻醉大鼠上观察肢体预缺血(limb ischemic preconditioning,LIP)对缺血-再灌注(ischemia—reperfusion,IR)心肌的影响,旨在探讨LIP对IR心肌有无保护效应,并明确腺苷和神经通路是否参与此效应。所得结果如下:(1)在心脏缺血30 min和再灌注120 min过程中,梗塞心肌占缺血心肌的51.48±0.82％。(2)LIP时心肌梗塞范围为35.14±0.88％,较单纯心肌缺血-再灌注时显著减小(P<0.01),表明LIP对心肌有保护作用。(3)事先切断股神经可取消LIP的保护效应。(4)股动脉内局部给予腺苷(10nmol/kg),可模拟LIP对心肌的保护作用;心肌梗塞范围是37.28±1.68％,而股静脉内注射同等剂量腺苷则无保护作用。(5)股动脉内预先应用腺苷A.受体拈抗剂8-环戊-1,3-二丙基嘌呤(DPCPX)(32 nmol/kg)可部分阻断LIP诱发的心肌保护效应。以上结果表明,肢体短暂预缺血可减小心肌缺血-再灌注后的梗塞范围,而局部释放的腺苷和由此所激活的相关的神经通路在LIP的心肌保护中起重要作用。     

p38 MAPKα/β和ERK1/2在心肌缺氧预处理信号传递中的不同作用

建立培养乳鼠心肌细胞的缺氧／复氧(A／R)损伤模型和缺氧预处理(APC)模型,以细胞存活率、细胞内超氧化物趋化酶(SOD)活性、丙二醛(MDA)含量、培养上清液乳酸脱氢酶(LDH)活性作为反映心肌细胞损伤的指标。采用细胞外信号调节蛋白激酶(ERK1／2)抑制剂PD98059及丝裂素活化蛋白激酶p38α/β(p38α/β)阻滞剂SB203580干预模型,并以胶内原位磷酸化法测定ERK1／2和p38活性,借以探讨ERK1／2和p38α/β在缺氧预处理保护机制中的作用。结果表明：(1)在APC组,于预处理的缺氧时相给予PD98059,可以完全消除APC的延迟保护作用;在A／R组的缺氧时相加入PD98059对细胞损伤无影响;(2)在APC组的预处理缺氧时相给予p38α／β抑制剂SB203580并不能消除APC的保护作用,而在A／R组的持续缺氧时相给予SB203580则可显著减轻缺氧对细胞的损伤;(3)ERK1／2和p38总活性测定表明,缺氧可激活ERK1／2和p38,它们的活性在缺氧后4h时达到高峰,而经过APC处理后,两者活性高峰提前于缺氧后3h时出现,且峰值显著降低。上述结果提示,预处理过程中ERK1／2的激活可能是缺氧预处理延迟保护机制中细胞信号传递的重要环节,预处理阶段p38α/β的活化不参与APC诱导的延迟保护信号传递过程,p38的过度激活可能是缺氧／复氧损伤过程中的一个致损伤参与因素,而预处理抑制随后持续缺氧阶段p38的过度激活可能是其保护机制的一个环节。     

Kappa 阿片受体的抗缺血性心脏保护作用--信息机制

有证据表明,心脏细胞产生强腓肽和强腓肽类多肽,它们是kappa阿片受体(κ-0R)的激动剂。κ-0R是心脏一种优势的阿片受体,其激活可改变在体和离体心脏的功能。在正常和病理情况下,内源性κ-阿片肽可能通过自分泌或旁分泌的方式调节心脏功能。心肌缺血是导致心脏功能紊乱的一个常见原因,主要表现为心肌功能减弱,心律失常及心肌梗塞等。心肌缺血时,交感神经发放增强,从而增加作功负荷及氧消耗量;而这又使缺血引发的状况更为恶化。机体抵抗缺血引发心肌损害／心律失常的保护机制之一是抑制β-肾上腺素受体(β—AR)的兴奋。κ-0R确实能抑制β-AR的激动。这种抑制主要是由于GS蛋白受到抑制,也在较小程度上由于信息通路的腺苷酸环化酶的抑制。因为该种酶能通过对百日咳毒素敏感的G蛋白转导β—AR的激动。另一保护心肌对抗缺血性损害的机制是预处理。预处理是指预先受到缺血等损伤使心脏对随后更严重的损伤产生较强的耐受能力。这种保护作用可以在预处理后即时产生,也可延至预处理后1—3天。在采用缺血或其产生的后果之一——代谢抑制作为预处理而致的心脏保护中,κ-OR参与媒介预处理的作用。用κ—OR的特异性激动剂U50488H激活κ—OR(U50488H药理性预处理,UP)可激活蛋白激酶C(PKC),开放ATY敏感的钾通道(KATP channels)及增加热休克蛋白(HSP)的产生。阻断PKC的作用,关闭KATP通道或抑制HSP的合成,均可消除UP的心脏保护作用。这些发现表明,PKC、KATP通道和HSP在UP的心脏保护中均具重要作用。此外,UP也能减低缺血造成心肌损害的因素之一,即Ca^2 的超负荷。这个事实表明UP发挥心脏保护作用至少部分地是通过减低Ca^2 的超负荷。最有趣的是,以阻断剂阻塞KATP通道,在消除UP的延迟性心脏保护作用的同时也降低了UP对Ca^2 超负荷的抑制作用。这个事实揭示了KATP通道开放所致的心脏保护作用至少部分地可能是由于防止或减低了Ca^2 的超负荷。     

代谢性谷氨酸受体配体(s)-4C3HPG对大鼠脑缺血耐受性诱导的影响

目的：观察侧脑室注射代谢型谷氨酸受体1／5亚型（mGluR1/5)配体（s)-4C3HPG对海马脑缺血耐受（BIT）诱导的影响,以探讨mGLUR1/5在BIT诱导中的作用。方法：采用大鼠四血管闭塞全脑缺血模型（4－vessel occlusion,4VO),应用硫堇染色和GFAP免疫组化法。36只大鼠椎动脉凝闭后分为sham组、单纯缺血组、BIT组和（s)-4C3HPG组,其中（s)-4C3HPG组又按所给药物剂量不同,分为0．2、0．04和0．008mg三个亚组。所有动物均在手术后或末次缺血后7d处死取材观察。结果：（1）单纯8min缺血可使海马CA1区组织学分级升高、锥体神经元密度降低和胶质纤维酸性蛋白（glial fibrillary acidic protein,GFAP)阳性表达增加（P＜0．05vs sham）.(2)BIT组未见单纯缺血组的上述变化,表明CIP可防止后续8min缺血造成的神经元损伤。（3）CIP的这种保护作用可被（s)-4C3HPG阻断,表现为海马CA1区组织学分级升高和锥体神经元密度降低（P＜0．05 vs sham)。这种变化与（s)-4C3HPG的剂量呈现明显的相关性,即剂量越大,上述改变越明显。结论：（s)-4C3HPG可阻断CIP诱导BIT的作用,提示mGluR1/5参与BIT的诱导。     

EGF Stimulates Growth by Enhancing Capacitative Calcium Entry in Corneal Epithelial Cells

In rabbit corneal epithelial cells (RCEC), we determined whether capacitative calcium entry (CCE) mediates the mitogenic response to epidermal growth factor, EGF. [Ca²⁺]_i was measured with single-cell fluorescence imaging of fura2-loaded RCEC. EGF (5 ng/ml) maximally increased [Ca²⁺]_i 4.4-fold. Following intracellular store (ICS) calcium depletion in calcium-free medium with 10 µM cyclopiazonic acid (CPA) (endoplasmic reticulum calcium ATPase inhibitor), calcium addback elicited plasma membrane Ca²⁺ influx as a result of activation of plasma membrane store operated channel (SOC) activity. Based on Mn²⁺ quench measurements of fura2 fluorescence, 5 ng/ml EGF enhanced such influx 2.3-fold, whereas with Rp-cAMPS (protein kinase A inhibitor) plus EGF it increased by 5.3-fold. In contrast, SOC activation was blocked with 100 µM 2-aminoethyldiphenylborate (2-APB, store-operated channel inhibitor). During exposure to either 50 µM UO126 (MEK-1/2 inhibitor) or 10 µM forskolin (adenylate cyclase activator), 5 ng/ml EGF failed to affect [Ca²⁺]_i. RT-PCR detected gene expression of: 1) transient receptor potential (TRP) protein isoforms 1, 3, 4, 6 and 7; 2) IP₃R isoforms 1–3. Immunocytochemistry, in conjunction with confocal and immunogold electron microscopy, detected plasma membrane localization of TRP4 expression. Inhibition of CCE with 2-APB and/or CPA, eliminated the 2.5-fold increase in intracellular [³H]-thymidine incorporation induced by EGF. Taken together, CCE in RCEC mediates the mitogenic response to EGF. EGF induces CCE through its stimulation of Erk1/2 activity, whereas PKA stimulation suppresses these effects of EGF. TRP4 may be a component of plasma membrane SOC activity, which is stimulated by ICS calcium depletion.     

Sensitivity analysis of stoichiometric networks: an extension of metabolic control analysis to non-steady state trajectories

A sensitivity analysis of general stoichiometric networks is considered. The results are presented as a generalization of Metabolic Control Analysis, which has been concerned primarily with system sensitivities at steady state. An expression for time-varying sensitivity coefficients is given and the Summation and Connectivity Theorems are generalized. The results are compared to previous treatments. The analysis is accompanied by a discussion of the computation of the sensitivity coefficients and an application to a model of phototransduction.     

缺血预处理对缺血再灌注后兔脊髓磷酸腺苷代谢的影响

目的：研究缺血参处理对缺血再灌注后兔脊髓磷酸腺苷代谢的影响。方法：往置入腹主动脉的Swan-Ganz导管气囊内注气造成兔腰髓缺血模型。将实验兔分为假手术组、缺血组和预处理组。应用反相高效液相色谱方法（reverse phase HPLC),对缺血再灌注后不同时间点腰髓组织中磷酸腺苷（ATP、ADP、AMP）的含量进行检测。结果：和假手术组相比,缺血组兔再灌后各时间点腰髓组织ATP含量有明显下降（P＜0．01）。与缺血组相应时间点相比,预处理组兔再灌注后腰髓组织ATP含量明显提高（P＜0．01）。结论：缺血预处理显著提高缺血再灌注后兔脊髓组织ATP含量,这可能是缺血预处理对脊髓缺血再灌注损伤产生保护作用的机制之一。