Four-million-year-Old hominids from East Lake Turkana,Kenya

A piece of mandible and several isolated teeth are reported from fluviatile sediments older than 4 million years at East Lake Turkana. They most closely resemble hominids from Laetoli, Tanzania and Hadar, Ethiopia which have been assigned to Australopithecus afarensis. © 1994 Wiley-Liss, Inc.     

中国对虾维生素营养的研究:Ⅰ.维生素A对中国对虾生长及视觉器官的影响

本文研究维生素Ａ对中国对虾（Ｐｅｎａｅｕｓ　ｃｈｉｎｅｎｓｉｓ）生长及视觉器官的影响,获得如下结果：１．体长 ４ｃｍ、体重１ｇ小虾对饲料中ＶＡ的最适添加量为 １８,０００ ＩＵ／１００ｇ饲料,体长８ｃｍ,体重７ｇ大虾对饲料 中ＶＡ的最适添加量为１２,０００ ＩＵ／１００ｇ饲料,在ＶＡ最适添加量下,对虾增长、增重最快,饲料系数最 低。２．中国对虾的视网膜电图在暗适应条件下有ｂ、ｃ、ｄ三波,在白、蓝、黄三种光照刺激下,只有Ａ３组 （１２,０００ＩＵ／１００ｇ饲料）其视网膜电位达最高值,即ｂ波振幅达２．４５ｍＶ,ｄ波振幅达３．７ｍＶ,表明ＶＡ 在最适添加量下,视觉反应灵敏,视觉功能正常; ３．ＶＡ最适添加量的 Ａ３组对虾眼组织完整、无畸变, 而ＶＡ含量过高或不足各组,其小眼、视网膜、髓体、Ｘ－器官等都有不同程度的畸变、不完整、干瘪等现 象,表明ＶＡ投喂量不当时,会引起视觉器官的发育障碍或病变。     

Biochemical genetics of methylglyoxal dehydrogenases in the laboratory rat (Rattus norvegicus)

A genetic locus controlling the electrophoretic mobility of a methylglyoxal dehydrogenase (EC 1.2.1.23) in the rat is described. The locus, designatedMgd1, is expressed in liver and kidney. Inbred rat strains have fixed either alleleMgd1 ^a or alleleMgd1 ^b . Codominant expression is observed in heterozygotes, providing evidence for a tetrameric enzyme structure. Backcross progenies showed the expected 1:1 segregation ratio, and there is evidence thatMgd1 is linked toPep3 andFh1 on chromosome 13. There is also evidence for two additional methylglyoxal dehydrogenases:Mgd2, present in liver and kidney, andMgd3, present only in heart.Supported by the Deutsche Forschungsgemeinschaft (Grant Be 352/18-1).     

Activation of mitogen activated protein (MAP) kinases by vanadate is independent of insulin receptor autophosphorylation

Treatment of Chinese hamster ovary (CHO) cells over-expressing the human insulin receptor (CHO-HIRc) with the insulin mimetic agent, vanadate, resulted in a dose- and time-dependent tyrosine phosphorylation of two proteins with apparent molecular sizes of 42 kDa (p42) and 44 kDa (p44). However, vanadate was unable to stimulate the tyrosyi phosphorylation of theβ-subunit of the insulin receptor. By using myelin basic protein (MBP) as the substrate to measure mitogen-activated protein (MAP) kinase activity in whole cell lysates, vanadate-stimulated tyrosyl phosphorylation of p42 and p44 was associated with a dose- and time-dependent activation of MAP kinase activity. Furthermore, affinity purification of cell lysates on anti-phosphotyrosine agarose column followed by immunoblotting with a specific antibody to MAP kinases demonstrated that vanadate treatment increased the tyrosyl phosphorylation of both p44^mapk and p42^mapk by several folds, as compared to controls, in concert with MAP kinase activation. In addition, retardation in gel mobility further confirmed that vanadate treatment increased the phosphorylation of p44^mapk and p42^mapk in CHO-HIRc. A similar effect of vanadate on MAP kinase tyrosyl phosphorylation and activation was also observed in CHO cells over-expressing a protein tyrosine kinase-deficient insulin receptor (CHO-1018). These results demonstrate that the protein tyrosine kinase activity of the insulin receptor may not be required in the signaling pathways leading to the vanadate-mediated tyrosyl phosphorylation and activation of MAP kinases.     

Ion channel regulation by calmodulin binding

While many ion channels are modulated by phosphorylation, there is growing evidence that they can also be regulated by Ca²⁺-calmodulin, apparently through direct binding. In some cases, this binding activates channels; in others, it modulates channel activities. These phenomena have been documented in Paramecium, in Drosophila, in vertebrate photoreceptors and olfactory receptors, as well as in ryanodine receptor Ca²⁺-release channels. Furthermore, studies on calmodulin mutants in Paramecium have shown a clear bipartite distribution of two groups of mutations in the calmodulin gene that lead to opposite behavioral and electrophysiological phenotypes. These results indicate that the N-lobe of calmodulin specifically interacts with one class of ion-channel proteins and the C-lobe with another.     

<Emphasis Type="Italic">Alona alsafadii</Emphasis> n. sp. from Yemen,a primitive,groundwater-dwelling member of the <Emphasis Type="Italic">A. karua</Emphasis>-group

The effect of algae on the production of musty-smelling compounds by actinomycetes was studied. Streptomyces spp., causing intensive musty odor, were isolated from hypertrophic Lake Kasumigaura and cultured in association with algae from the same lake. Isolate E and I effectively utilized the cyanobacteria, Microcystis aeruginosa and Anabaena spiroides, and the diatom, Synedra acus, as a carbon source and produced a musty-smelling 2-methylisoborneol in the shaken sediment cultures. High populations of algae and actinomycetes, and aerobic condition in the sediment seem responsible for the occurrence of musty odor in Lake Kasumigaura.     

Extracellular pH determines the rate of Ca2+ entry into Madin-Darby canine kidney-focus cells

We investigated the relationship between intracellular Ca²⁺ and pH homeostasis in Madin-Darby canine kidney-focus (MDCK-F) cells, a cell line exhibiting spontaneous oscillations of intracellular Ca²⁺ concentration (Ca _i ²⁺ ). Ca _i ²⁺ and intracellular pH (pH _i ) were measured with the fluorescent dyes Fura-2 and BCECF by means of video imaging techniques. Ca²⁺ influx from the extracellular space into the cell was determined with the Mn²⁺ quenching technique. Cells were superfused with HEPES-buffered solutions. Under control conditions (pH 7.2), spontaneous Ca _i ²⁺ oscillations were observed in virtually all cells investigated. Successive alkalinization and acidification of the cytoplasm induced by an ammonia ion prepulse had no apparent effect on Ca _i ²⁺ oscillations. On the contrary, changes of extracellular pH value strongly affected Ca _i ²⁺ oscillations. Extracellular alkalinization to pH 7.6 completely suppressed oscillations, whereas extracellular acidification to pH 6.8 decreased their frequency by 40%. Under the same conditions, the respective pH _i changes were less than 0. 1 pH units. However, experiments with the Mn²⁺ quenching technique revealed that extracellular alkalinization significantly reduced Ca²⁺ entry from the extracellular space. Large increases of Ca _i ²⁺ triggered by the blocker of the cytoplasmic Ca²⁺-ATPase, thapsigargin, had no effect on pH _i We conclude: intracellular Ca²⁺ homeostasis in MDCK-F cells is pH dependent. pH controls Ca²⁺ homeostasis mainly by effects on the level of Ca²⁺ entry across the plasma membrane. On the contrary, the intracellular pH value seems to be insensitive to rapid changes of Ca _i ²⁺ .The project was supported by the Deutsche Forschungsgemeinschaft, SFB-176 (A6) and by the Jubilämusstiftung of the University of Würzburg.The authors gratefully acknowledge the valuable discussions with Drs. M.J. Berridge, M. Carew, I. Davidson, G. Law and B. Somasundraman. We are grateful to Applied Imaging for financial and technical support and to the Medical Research Council for financial support.     

Adenosine discriminates between the caffeine and adenine nucleotide sites on the sheep cardiac sarcoplasmic reticulum calcium-release channel

Calcium-release channels of sheep cardiac sarcoplasmic reticulum were incorporated into phosphatidylethanolamine bilayers and single channel currents were recorded under voltage-clamp conditions. The effect of adenosine on single channel conductance and gating was investigated, as were the interactions between adenosine and caffeine and adenosine and ,-methylene ATP.Addition of adenosine (0.5–5 mm) to the cytosolic but not the luminal side of the membrane increased the open probability of single calcium-activated calcium-release channels by increasing the frequency and duration of open events, yielding an EC₅₀ of 0.75 mm at 10 m activating Ca²⁺.Addition of 1 mm caffeine potentiated the effects of adenosine at 10 or 100 m-activating cytosolic calcium, but had no effect on the inability of adenosine to activate the channel at 80 pmcalcium, suggesting discrete sites of action on the calcium-release channel for adenosine and caffeine. In contrast, addition of 100 m ,-methylene-ATP decreased single channel open probability in the presence of adenosine, suggesting that these compounds act on the same site on the channel.Activation of single channel opening by adenosine, or by adenosine together with caffeine, had no effect on single channel conductance or the Ca²⁺/Tris⁺ permeability ratio. Channels activated by adenosine were characteristically modified by ryanodine and blocked by m ruthenium red or mm magnesium.These results show that adenosine activates the sheep cardiac sarcoplasmic reticulum Ca²⁺-release channel by increasing the frequency and duration of open events in a Ca²⁺-dependent manner. The receptor site on the channel for adenosine is distinct from that for caffeine but probably the same as that for adenine nucleotides.This work was supported by the British Heart Foundation.     

Properties of the K+ inward rectifier in the plasma membrane of xylem parenchyma cells from barley roots: Effects of TEA+, Ca2+, Ba2+ and La3+

Xylem parenchyma cells are situated around the (apoplastic) xylem vessels and are involved in the control of the composition of the xylem sap by exporting and resorbing solutes. We investigated properties of the K⁺ inward rectifier in the plasma membrane of these cells by performing patch clamp experiments on protoplasts in the whole-cell configuration. Inward currents were sensitive to the K⁺ channel blocker TEA⁺ at a high concentration (20 mm). Barium, another classical K⁺ channel blocker, inhibited K⁺ currents with a K _i of about 1.3 mm. In contrast to guard cells, the cytosolic Ca²⁺ level proved to be ineffective in regulating the K⁺ conductance at hyperpolarization. External Ca²⁺ blocked currents weakly in a voltage-dependent manner. From instantaneous current-voltage curves, we identified a binding site in the channel pore with an electrical distance of about 0.2 to 0.5. Lanthanum ions reduced the inward current in a voltage-dependent manner and simultaneously displaced the voltage at which half of the channels are in the open state to more positive values. This finding was interpreted as resulting from a sum of two molecular effects, an interaction with the mouth of the channel that causes a reduction of current, and a binding to the voltage sensor, leading to a shielding of surface charges and, subsequently, a modulation of channel gating.A comparison between the K⁺ inward rectifier in xylem parenchyma cells, guard cells and KAT1 from Arabidopsis leads to the conclusion that these rectifiers form subtypes within one class of ion channels. The ineffectiveness of Ca²⁺ to control K⁺ influx in xylem parenchyma cells is interpreted in physiological terms.