Removal of sodium inactivation and block of sodium channels by chloramine-T in crayfish and squid giant axons.

Modification of sodium channels by chloramine-T was examined in voltage clamped internally perfused crayfish and squid giant axons using the double sucrose gap and axial wire technique, respectively. Freshly prepared chloramine-T solution exerted two major actions on sodium channels: (a) an irreversible removal of the fast Na inactivation, and (b) a reversible block of the Na current. Both effects were observed when chloramine-T was applied internally or externally (5-10 mM) to axons. The first effect was studied in crayfish axons. We found that the removal of the fast Na inactivation did not depend on the states of the channel since the channel could be modified by chloramine-T at holding potential (from -80 to -100 mV) or at depolarized potential of -30 mV. After removal of fast Na inactivation, the slow inactivation mechanism was still present, and more channels could undergo slow inactivation. This result indicates that in crayfish axons the transition through the fast inactivated state is not a prerequisite for the slow inactivation to occur. During chloramine-T treatment, a distinct blocking phase occurred, which recovered upon washing out the drug. This second effect of chloramine-T was studied in detail in squid axons. After 24 h, chloramine-T solution lost its ability to remove fast inactivation but retained its blocking action. After removal of the fast Na inactivation, both fresh and aged chloramine-T solutions blocked the Na currents with a similar potency and in a voltage-dependent manner, being more pronounced at lower depolarizing potentials.(ABSTRACT TRUNCATED AT 250 WORDS)     

Uniformly oriented gramicidin channels embedded in thick monodomain lecithin multilayers.

Phosphatidylcholine multilayers, containing 20% water by total sample weight and gramicidin/lipid molar ratios up to 1:40 were aligned by low temperature annealing (less than 60 degrees C) and mechanical stressing. We were able to obtain large (greater than 80 micron thick X 40 mm2 area) monodomain defect-free multilayers containing approximately 10(17) uniformly oriented gramicidin channels. The alignment of lipid multilayers was monitored by conoscopy and polarized microscopy. The smectic defects, which appeared during the alignment process, were identified and dissolved. The incorporation of gramicidin into the multilayers in the form of transmembrane channels was indicated by its circular dichroic (CD) spectrum. A well-defined CD spectrum of uniformly oriented gramicidin channels was obtained. The oriented samples will allow spectroscopic studies of the ion channel in its conducting state and diffraction studies of the channel-channel organization in the membrane.     

Alteration of protein phosphorylation patterns in cell lines morphologically transformed by human cytomegalovirus

Human fibroblastic cell lines morphologically transformed by either live virus or DNA fragments of human cytomegalovirus had altered plasma membrane protein composition; quantitative changes, and gains and losses in protein composition in comparison to normal parent cell lines were detected. These transformed cell lines showed altered total cell protein phosphorylation patterns when compared to parent cell lines. A two to four fold increase in in vivo protein phosphorylation at serine and threonine residues was observed; no increase in phosphorylation at total cell tyrosine residues was detected. Analysis of the in vivo phosphorylated protein by two dimensional gel electrophoresis revealed some similarities as well as differences in the types of polypeptides phosphorylated between transformed and control cell lines. Increased (two-to sixfold over parent cell extracts) casein kinase and polyamine dependent casein kinase activities were detected in HCMV transformed cell extracts.     

Posttreatment with sodium arsenite is coclastogenic in log phase but not in stationary phase

Summary Posttreatment with sodium arsenite in log phase synergistically increases the chromosomal aberrations induced by ethyl methanesulfonate in Chinese hamster ovary cells, human fibroblasts, and human lymphocytes. However, posttreatment with sodium arsenite in stationary phase has no apparent effect on the clastogenicity of ethyl methanesulfonate. These results indicate that the cycling state of the cell plays a crucial role in the action of arsenite coclastogenicity. One prediction from this finding is that in combined treatment, posttreatment with sodium arsenite should preferentially kill cancer cells.     

嘉兰栽培及其秋水仙碱含量测定

嘉兰原属热带性地区的植物,但从云南南部引种到广州地区种植。表现生长发育良好,且其秋水仙碱含量高达0.40—0.45％。是一种有推广种植价植的药用植物。     

广西北部罗汉果根结线虫病研究

罗汉果根结线虫是罗汉果的一个重要病害。在室内盆栽接种条件下,该线虫年发生6代。本文叙述了线虫的生物学及其寄主植物。防治试验结果表明。穴施灭克磷等是有效的。土壤翻晒也能消灭大部分土中线虫,病薯用热处理也有很好的效果。     

中药灵香草及其混淆品种的比较鉴别

本文比较了中药灵香草Lysimachia foenum-graecum Hance及其混淆品种垂花香草Lysimaehia nutantiflora Chen et C.M.Hu的植物形态、药材性状以及茎、叶组织显微特征。指出垂花香草无灵香草特有的芳香。也无药用记载。应仔细区别,不宜混用。     

Gene deletion, a mechanism of induced mutation by arabinosyl nucleosides

9-β- -Arabinofuranosyl-2-fluoroadenine (F-ara-A) and 9-β- -arabinofuranosyladenine (ara-A) are purine nucleoside analogues which are incorporated into nucleic acids. This study demonstrates the mutagenic properties of F-ara-A and ara-A and provides evidence for mechanisms by which the arabinosyl nucleosides induce mutation. At the drug dosages that evoked exponential cell killing, F-ara-A and ara-A caused a significant increase in the number of 6-thioguanine-resistant mutants in Chinese hamster ovary cells. Southern analyses showed that 15 of 16 drug-induced mutants had lost all or part of the HPRT gene, whereas no loss of the gene was found in 4 spontaneous mutants. We conclude that both F-ara-A and ara-A induced mutation predominantly by causing deletion of genetic method. The remarkable frequency of gene deletion among these drug-induced mutations is discussed with respect to possible mechanisms of action of arabinosyl nucleosides in mutational studies.     

Maintenance of low cl concentrations in mesophyll cells of leaf blades of barley seedlings exposed to salt stress

The concentrations of vacuolar Na⁺ and Cl⁻ in the epidermal and mesophyll cells of the leaf blade and sheath of Hordeum vulgare seedlings (cv California Mariout and Clipper) were measured by means of quantitative electron probe x-ray microanalysis. A preferential accumulation of Cl⁻ in vacuoles of epidermal cells in both blade and sheath and a low level in mesophyll cells of the blade were evident in plants grown in full strength Johnson solution. The concentration of Cl⁻ in the mesophyll cells of the blade remained at a low level after exposure to 50 or 100 millimolar NaCl for 1 day or to 50 millimolar for 4 days, while at the same time the concentration of Cl⁻ in the epidermis and mesophyll of the sheath showed a dramatic increase. Clipper generally contained more Cl⁻ in the mesophyll cells of the blade than California Mariout. A greater accumulation of Na⁺ in the mesophyll of the sheath relative to that of the blade was only apparent after treatment with 100 millimolar NaCl for 1 day or 50 millimolar for 4 days. These results confirm the suggestion that sheath tissue is capable of accumulating excess Cl⁻ (and to a lesser extent Na⁺) and suggest that the site of regulation of Cl⁻ concentration in the barley leaf is located in the mesophyll cells of the blade.     

Lysophosphatidate acyltransferase activities in the microsomes from palm endosperm, maize scutellum, and rapeseed cotyledon of maturing seeds

Lysophosphatidate (LPA) acyltransferase (EC 2.3.1.51) in the microsomes from palm endosperm (Syagrus cocoides Martius), maize scutellum (Zea mays L.), and rapeseed cotyledon (Brassica napus L.) of maturing seeds were studied for their specificities toward the acyl moiety of the substrates lysophosphatidate and acyl coenzyme A (CoA). The LPA acceptor greatly influenced the acyl CoA specificity of the enzyme and vice versa. With 1-oleoyl-lysophosphatidate (LPA-18:1), the palm enzyme was equally active on oleoyl CoA and lauroyl CoA, whereas the maize and rapeseed enzymes were more active on oleoyl CoA than on lauroyl CoA. With 1-lauroyl-lysophosphatidate (LPA-12), which generated less activity than LPA-18:1, the palm enzyme was three times more active on lauroyl CoA than on oleoyl CoA. LPA-12 was an inactive substrate for the maize and rapeseed enzymes. The selectivity of the enzymes was also studied using a mixture of LPA-18:1 and LPA-12, as well as lauroyl CoA and oleoyl CoA. Under this selectivity condition and compared to the specificity condition, the enzymes from all the three seeds exerted stronger preference for oleoyl moiety in either the LPA or acyl CoA, and again, only the palm enzyme could act on LPA-12. Similar studies, although in lesser detail, showed that the enzymes from soybean and castor bean were similar to the maize and rapeseed enzymes in having little activity on substrates containing lauroyl moiety. The results demonstrate the importance of the acyl group in the sn-1 position of LPA in determining the acyl preference in the sn-2 position in phosphatidate synthesis. The palm enzyme appears to be the only one capable of synthesizing phosphatidates containing high amounts of lauric moieties.