Membrane electrical parameters in turtle bladder measured using impedance-analysis techniques

Summary Equivalent-circuit impedance analysis experiments were performed on the urinary bladders of freshwater turtles in order to quantify membrane ionic conductances and areas, and to investigate how changes in these parameters are associated with changes in the rate of proton secretion in this tissue. In all experiments, sodium reabsorption was inhibited thereby unmasking the electrogenic proton secretion process. We report the following: (1) transepithelial impedance is represented exceptionally well by a simple equivalent-circuit model, which results in estimates of the apical and basolateral membrane ionic conductances and capacitances; (2) when sodium transport is inhibited with mucosal amiloride and serosal ouabain, the apical and basolateral membrane conductances and capacitances exhibit a continual decline with time; (3) this decline in the membrane parameters is most likely caused by subtle time-dependent changes in cell volume, resulting in changes in the areas of the apical and basolateral membranes; (4) stable membrane parameters are obtained if the tissue is not treated with ouabain, and if the oncotic pressure of the serosal solution is increased by the addition of 2% albumin; (5) inhibition of proton secretion using acetazolamide in CO₂ and HCO ₃ ^– -free bathing solutions results in a decrease in the area of the apical membrane, with no significant change in its specific conductance; (6) stimulation of proton transport with CO₂ and HCO ₃ ^– -containing serosal solution results in an increase in the apical membrane area and specific conductance. These results show that our methods can be used to measure changes in the membrane electrophysiological parameters that are related to changes in the rate of proton transport. Notably, they can be used to quantify in the live tissue, changes in membrane area resulting from changes in the net rates of endocytosis and exocytosis which are postulated to be intimately involved in the regulation of proton transport.     

Refolding of trypsin-subtilisin inhibitor from marine turtle eggwhite

Trypsin-subtilisin inhibitor from marine turtle eggwhite refolded quantitatively from its fully reduced state atpH 8.5 in the presence of reduced and oxidized glutathione. The refolding process was studied by following the accompanying changes in inhibitory activity, fluorescence, sulfhydryl group titer, and hydrodynamic volume. The refolding process followed second-order kinetics with rate constants of 4.80×10² M^–1 sec^–1 for trypsin-inhibiting domain and 0.77× 10² M^–1 sec^–1 for subtilisin-inhibiting domain of the inhibitor at 30°C and their respective activation energies of the refolding process were 15.9 and 21.6 kcal/mol. Fluorescence intensity of the reduced inhibitor decreased with time of refolding until it corresponded to the intensity of the native inhibitor. The inhibitor contained 1–2%-helix, 40–42%-sheet, and 57–58% random coil structure. Refolded inhibitor gave a circular dichroic spectrum identical to that of the native inhibitor. A number of principal intermediates were detected as a function of the refolding time. Size-exclusion chromatography separated the intermediates differing in hydrodynamic volume (Stokes radius). The Stokes radius ranged from 23 Å (fully reduced inhibitor) to 18.8 Å (native inhibitor). Results indicated the independent refolding of two domains of the inhibitor and multiple pathways of folding were followed rather than an ordered sequential pathway.     

Temporal-spatial variation and the influence factors of precipitation in Sichuan Province, China

Precipitation is a key factor in the water cycle. At the same time, precipitation is the focus of study in meteorology and climatology, ecological environmental assessment, non-point source pollution and so on. Understanding the temporal-spatial variation and the corresponding factors of precipitation has become the object of hydrology and environmentology. Based on the annual precipitation data, we analyzed the spatial distribution of precipitation in Sichuan Province in China as well as the temporal-spatial variation and the corresponding influence factors involved. The results show that the amount of precipitation was abundant, but the spatial distribution was not consistent with it and the amount of precipitation gradually declined from the south-east to the north-west in Sichuan Province, China. Moreover, the spatial distribution was different throughout the years. The result of correlation analysis indicated that elevation, temperature and air pressure were three key factors affecting the amount and distribution of precipitation, and the correlation coefficients were −0.56, 0.38 and 0.45 respectively. Notably, the relationship between the slope of topography and precipitation were significantly negative and the average correlation coefficient was −0.28.     

川中人工纯柏林凋落物分解动态研究

对柏木人工纯林的渊落物有机碳和一些营养元素的分解和释放过程的研究表明,柏木凋落物中有机碳和营养元素的矿化非常缓慢,凋落物有机碳的半减期是33周,氮素矿化半减期是433周,磷矿化半减期是10周,钾矿化半减期是24周,钙矿化半减期是86周,镁矿化半减期是12周。柏木早期生长缓慢、成林困难主要是受氮素不足的制约。在林分改造和营林中适当增加阔叶速生树种,改善凋落物性质．对促进凋落物分解和养分周转、改善土壤养分状况、提高柏木人工林的生态和经济效益是很必要的。     

Tracking changing environments using stable carbon isotopes in fossil tooth enamel: an example from the South African hominin sites

The environmental contexts of the karstic hominin sites in South Africa have been established largely by means of faunal associations; taken together these data suggest a trend from relatively closed and more mesic to open, drier environments from about 3 to 1.5 Ma. Vrba argued for a major shift within this trend ca. 2.4-2.6 Ma, an influential proposal that posited links between bovid (and hominin) radiation in Africa and the intensification of Northern Hemisphere Glaciation. Yet faunal approaches often rely on habitat and feeding preferences of modern taxa that may differ from those of their extinct predecessors. Here we explore ways of extending ¹³C/¹²C data from fossil mammals beyond denoting “presence” or “absence” of C₄ grasses using the evolution of open environments in South Africa as a case study. To do so we calculated the relative proportions of C₃-, mixed-, and C₄-feeding herbivores for all the hominin sites for which we have sufficient data based on ¹³C/¹²C analyses of fossil tooth enamel. The results confirm a general trend towards more open environments since 3 Ma, but they also emphasize a marked change to open grassy habitats in the latest Pliocene/early Pleistocene. Mean ¹³C/¹²C for large felids also mirrored this trend.     

现代人起源问题的新争论

现代人在分类学上称为晚期智人。他们是怎样起源的?长期来有两种理论,一种叫直接演化说(Direct evolution hypothesis)或系统说,也叫多地区起源说。这种理论认为现代人是由当地的早期智人以至猿人演化而来的,各人种在很久以前即已分歧,各自平行发展,演化成现代人,但长时期来互相有基因的交流。例如欧洲的白种人是由当地的尼安德特人逐渐演变来的;亚洲的黄种人是由当地的早期智人和猿人演变来的。另一种理论叫入侵论(Invasion hypothesis),也叫迁徙说或代替说,这种理论认为欧洲是典型尼人的家乡, 而解剖结构上的现代人是在欧洲以外地区演化出来, 然后侵人欧洲的尼人区域, 消灭了土著的尼人而形成的;侵人亚洲的也一样, 形成现代的黄种人。这种单一地区起源说过去一般认为亚洲西部是现代人最早形成的地区, 近年来有人提出非洲南部才是现代人最早形成的地区, 然后迁徙到世界各地。     

四川省藓类植物新记录

在对四川省第一高峰贡嘎山的野外调查和1 000余份采集标本鉴定的基础上,现已知贡嘎山有藓类植物40科,133属,321种.其中,隶属于10科,12属的12种为四川省苔藓植物新记录种.该文就新记录种进行详细报道,为中国和四川省的苔藓植物区系研究提供新的资料.     

榆属（榆科）一新种——绵竹榆

绵竹榆的花秋季开放,翅果柱头面被毛,其两侧的翅较果核为窄,果核位于翅果上端接近缺口处,与榔榆(Ulmus parvifolia Jacq.)相似,但树皮深灰色,不规则鳞块状浅裂,叶片先端渐尖,花被片裂至基部,宿存,边缘上部生纤毛,翅果狭椭圆形,中部最宽,向两端渐变窄,果梗与花被等长,长约2 mm,果序梗长约1 mm,而明显不同。