A Start Point for Extracellular Nucleotide Signaling

A START POINT FOR EXTRACELLULAR NUCLEOTIDE SIGNALING
The recent discovery of a plant receptor for extracellu- lar nucleotides, reported by Choi et al. （2014）, is a major breakthrough that had been anticipated for over a dec- ade. Plants release ATP into their extracellular matrix （ECM） during growth and when they are induced by vari- ous biotic and abiotic stimuli （Clark and Roux, 2011）. That these extracellular nucleotides would activate receptors in plants was predicted by two sets of discoveries： that low- and sub-micromolar ATP could induce increases in [Ca2＋]cyt, NO, and superoxide signaling intermediates that led to downstream growth, stomatal, and defense responses, and that these changes could be blocked by antagonists that blocked extracellular nucleotide receptors in animals （Demidchik et al., 2003; Song et al., 2006; Clark et al., 2011; Demidchik et al., 2009, 2011）. Although mammalian biolo- gists had discovered two classes of receptors for extracel- lular nucleotides （P2X and P2Y） decades ago （Burnstock, 2007）, there were no plant proteins obviously similar to these in any sequence data available. Clearly, if there were plant purinoceptors, they would be different from the mammalian receptors, and they could not be discovered by motif searches.     

Dependence of Na+-Ca2+ exchange and Ca2+-Ca2+ exchange on monovalent cations

Two mechanisms of passive Ca2+ transport, Na+-Ca2+ exchange and Ca2+-Ca2+ exchange, were studied using highly-purified dog heart sarcolemmal vesicles. About 80% of the Ca2+ accumulated by Na+-Ca2+ exchange or Ca2+-Ca2+ exchange could be released as free Ca2+, while up to 20% was probably bound. Na+-Ca2+ exchange was simultaneous, coupled countertransport of Na+ and Ca2+. The movement of anions during Na+-Ca2+ exchange did not limit the initial rate of Na+-Ca2+ exchange. Na+-Ca2+ exchange was electrogenic, with a reversal potential of about -105 mV. The apparent flux ratio of Na+-Ca2+ exchange was 4 Na+:1 Ca2+. Coupled cation countertransport by the Na+-Ca2+ exchange mechanism required a monovalent cation gradient with the following sequence of ion activation: Na+ much greater than Li+ greater than Cs+ greater than K+ greater than Rb+. In contrast to Na+-Ca2+ exchange, Ca2+-Ca2+ exchange did not require a monovalent cation gradient, but required the presence of Ca2+ plus a monovalent cation on both sides of the vesicle membrane. The sequence of ion activation of Ca2+-Ca2+ exchange was: K+ much greater than Rb+ greater than Na+ greater than Li+ greater than Cs+. Na+ inhibited Ca2+-Ca2+ exchange when Ca2+-Ca2+ exchange was supported by another monovalent cation. Both Na+-Ca2+ exchange and Ca2+-Ca2+ exchange were inhibited, but with different sensitivities, by external MgCl2, quinidine, or verapamil.     

A phylogenetic analysis of the extant Aeshnidae (Odonata: Anisoptera)

Abstract A cladistic analysis of the world Aeshnidae is presented, based on fifty-eight characters of adult and larval anatomy. The ingroup taxa include all the extant genera of Aeshnidae, and the austropetaliid genera Phyllopetalia and Hypopetalia were chosen as the outgroup. The strict consensus tree obtained after successive weighting shows that the subgroups defined traditionally for Aeshnidae are paraphyletic or polyphyletic. The previous reclassification derived from analyses based on wing venation is supported in terms of the monophyly of Aeshnidae, Gomphaeschninae and its sister group comprising the remaining Aeshnidae. Gomphaeschninae is confirmed as sister group of the remaining Aeshnidae (= Aeshnodea Bechly). The sister-group relationships between Gomphaeschna + Sarasaeschna and Linaeschna + Oligoaeschna are corroborated. Within Aeshnodea, three monophyletic groups emerged: Boyeria + ( Petaliaeschna + ( Limnetron + Gynacanthaeschna + Periaeschna )) + (( Cephalaeschna + Caliaeschna ) + ( Allopetalia ( Notoaeschna + Spinaeschna ))); Dendroaeschna + ( Epiaeschna + ( Aeschnophlebia + ( Nasiaeschna + ( Tetracanthagyna + Brachytron )))); and Polycanthagyna + ( Basiaeschna + ( Amphiaeschna + ( Indaeschna + ( Oplonaeschna + ( Racenaeschna + Plattycantha + Agyrtacantha + Triacanthagyna + ( Subaeschna + Austrogynacantha + Gynacantha ) + ( Heliaeschna + ( Neuraeschna + Staurophlebia ))) + (( Castoraeschna + Coryphaeschna + Remartinia ) + ( Oreaeschna + ( Aeshna + ( Anaciaeschna + ((' A .' isosceles + Andaeshna ) + ( Anax + Hemianax )))))). Additional informative characters are required to test the relationships suggested here between the main groups of Aeshnodea and some enigmatic basal taxa ( Antipodophlebia , Austroaeschna , Acanthaeschna , Telephlebia , Austrophlebia and Planaeschna ).     

不同利用方式下稻田效益的综合评价

一、引言评价是多目标系统优化和决策的基础。和任何其他农业生态系统一样,稻田生态系统具有多目标、多功能的特点,单项指标难以反映系统的优劣。目前,川东南地区稻田开发利用方式多种多样,但效益评价主要是采用简单的比较分析或粗放的定性描述,尚未形成系统的     

Ligand-dependent reactivity of (Na+ + K+)-ATPase with showdomycin

Showdomycin inhibited pig brain (Na+ + K+)-ATPase with pseudo first-order kinetics. The rate of inhibition by showdomycin was examined in the presence of 16 combinations of four ligands, i.e., Na+, K+, Mg2+ and ATP, and was found to depend on the ligands added. Combinations of ligands were divided into five groups in terms of the magnitude of the rate constant; in the order of decreasing rate constants these were: (1) Na+ + Mg2+ + ATP, (2) Mg2+, Mg2+ + K+, K+ and none, (3) Na+ + Mg2+, Na+, K+ + Na+ and Na+ + K+ + Mg2+, (4) Mg2+ + K+ + ATP, K+ + ATP and Mg2+ + ATP, (5) K+ + Na + + ATP, Na+ + ATP, Na+ + K+ + Mg2+ + ATP and ATP. The highest rate was obtained in the presence of Na+, Mg2+ and ATP. The apparent concentrations of Na+, Mg2+ and ATP for half-maximum stimulation of inhibition (KS0.5) were 3 mM, 0.13 mM and 4 MicroM, respectively. The rate was unchanged upon further increase in Na+ concentration from 140 to 1000 mM. The rates of inhibition could be explained on the basis of the enzyme forms present, including E1, E2, ES, E1-P and E2-P, i. e., E2 has higher reactivity with showdomycin than E1, while E2-P has almost the same reactivity as E1-P. We conclude that the reaction of (Na+ + K+)- ATPase proceeds via at least four kinds of enzyme form (E1, E2, E1 . nucleotide and EP), which all have different conformations.     

Na+-inhibitory sites of the Na+/H+ exchanger are Li+ substrate sites

Amiloride-inhibitable Li+ influx in dog red blood cells is mediated by the Na+/H+ exchanger, NHE. However, there are substantial differences between the properties of Li+ transport and Na+ transport through the NHE. Li+ influx is activated by cell shrinkage, and Na+ influx is not, as we reported previously (Dunham PB, Kelley SJ, and Logue PJ. Am J Physiol Cell Physiol 287: C336-C344, 2004). Li+ influx is a sigmoidal function of its concentration, and Na+ activation is linear at low Na+ concentrations. Li+ does not inhibit its own influx; in contrast, Na+ inhibits Na+ influx. Li+ prevents this inhibition by Na+. Na+ is a mixed or noncompetitive inhibitor of Li+ influx, implying that both a Na+ and a Li+ can be bound at the same time. In contrast, Li+ is a competitive inhibitor of Na+ influx, suggesting Li+ binding at one class of sites on the transporter. Because the properties of Li+ transport and Na+ transport are different, a simple explanation is that Na+ and Li+ are transported by separate sites. The similarities of the properties of Li+ transport and the inhibition of Na+ transport by Na+ suggest that Li+ is transported by the Na+-inhibitory sites.     

Identification and characterization of genes involved in the jasmonate biosynthetic and signaling pathways in mulberry （Morus notabilis）

Jasmonate （JA） is an important phytohormone regulating growth, development, and environmental response in plants, particularly defense response against herbivorous insects. Recently, completion of the draft genome of the mulberry （Morus notabilis） in conjunction with genome sequencing of silkworm （Bombyx mori） provides an opportuni-ty to study this unique plant-herbivore interaction. Here, we identified genes involved in JA biosynthetic and signaling pathways in the genome of mulberry for the first time, with the majority of samples showing a tissue-biased expression pattern. The analysis of the representative genes 12-oxophy-todienoic acid reductase （OPRs） and jasmonate ZIM-domain （JAZs） was performed and the results indicated that the mulberry genome contains a relatively smal number of JA biosynthetic and signaling pathway genes. A gene encoding an＆amp;nbsp;important repressor, MnNINJA, was identified as an alternative splicing variant lacking an ethylene-responsive element binding factor-associated amphiphilic repression motif. Having this fundamental information wil facilitate future functional study of JA-related genes pertaining to mulberry-silkworm interactions.     

Control of brain slice respiration by (Na+ + K+)-activated adenosine triphosphate and the effects of enzyme inhibitors.

The involvement of membrane (Na+ + K+)-ATPase (Mg2+-dependent, (Na+ + K+)-activated ATP phosphohydrolase, E.C. 3.6.1.3) in the oxygen consumption of rat brain cortical slices was studied in order to determine whether (Na+ + K+)-ATPase activity in intact cells can be estimated from oxygen consumption. The stimulation of brain slice respiration with K+ required the simultaneous presence of Na+. Ouabain, a specific inhibitor of (Na+ + K+)-ATPase, significantly inhibited the (Na+ + K+)-stimulation of respiration. These observations suggest that the (Na+ + K+)-stimulation of brain slice respiration is related to ADP production as a result of (Na+ + K+)-ATPase activity. However, ouabain also inhibited non-K+ -stimulated respiration. Additionally, ouabain markedly reduced the stimulation of respiration by 2,4-dinitrophenol in a high (Na+ + K+)-medium. Thus, ouabain depresses brain slice respiration by reducing the availability of ADP through (Na+ + K+)-ATPase inhibition and acts additionally by increasing the intracellular Na+ concentration. These studies indicate that the use of ouabain results in an over-estimation of the respiration related to (Na+ + K+)-ATPase activity. This fraction of the respiration can be estimated more precisely from the difference between slice respiration in high Na+ and K+ media and that in choline, K+ media. Studies were performed with two (Na+ + K+)-ATPase inhibitors to determine whether administration of these agents to intact rats would produce changes in brain respiration and (Na+ + K+)-ATPase activity. The intraperitoneal injection of digitoxin in rats caused an inhibition of brain (Na+ + K+)-ATPase and related respiration, but chlorpromazine failed to alter either (Na+ + K+)-ATPase activity or related respiration.     

The effect of Mg2+ on hepatic microsomal Ca2+ and Sr2+ transport

The ATP-dependent uptake of Ca2+ by rat liver microsomal fraction is dependent upon Mg2+. Studies of the Mg2+ requirement of the underlying microsomal Ca2+-ATPase have been hampered by the presence of a large basal Mg2+-ATPase activity. We have examined the effect of various Mg2+ concentrations on Mg2+-ATPase activity, Ca2+ uptake, Ca2+-ATPase activity and microsomal phosphoprotein formation. Both Mg2+-ATPase activity and Ca2+ uptake were markedly stimulated by increasing Mg2+ concentration. However, the Ca2+-ATPase activity, measured concomitantly with Ca2+ uptake, was apparently unaffected by changes in the Mg2+ concentration. In order to examine the apparent paradox of Mg2+ stimulation of Ca2+ uptake but not of Ca2+-ATPase activity, we examined the formation of the Ca2+-ATPase phosphoenzyme intermediate and formation of a Mg2+-dependent phosphoprotein, which we have proposed to be an attribute of the Mg2+-ATPase activity. We found that Ca2+ apparently inhibited formation of the Mg2+-dependent phosphoprotein both in the absence and presence of exogenous Mg2+. This suggests that Ca2+ may inhibit (at least partially) the Mg2+-ATPase activity. However, inclusion of the Ca2+ inhibition of Mg2+-ATPase activity in the calculation of Ca2+-ATPase activity reveals that this effect is insufficient to totally account for the stimulation of Ca2+ uptake by Mg2+. This suggests that Mg2+, in addition to stimulation of Ca2+-ATPase activity, may have a direct stimulatory effect on Ca2+ uptake in an as yet undefined fashion. In an effort to further examine the effect of Mg2+ on the microsomal Ca2+ transport system of rat liver, the interaction of this system with Sr2+ was examined. Sr2+ was sequestered into an A23187-releasable space in an ATP-dependent manner by rat liver microsomal fraction. The uptake of Sr2+ was similar to that of Ca2+ in terms of both rate and extent. A Sr2+-dependent ATPase activity was associated with the Sr2+ uptake. Sr2+ promoted formation of a phosphoprotein which was hydroxylamine-labile and base-labile. This phosphoprotein was indistinguishable from the Ca2+-dependent ATPase phosphoenzyme intermediate. Sr2+ uptake was markedly stimulated by exogenous Mg2+, but the Sr2+-dependent ATPase activity was unaffected by increasing Mg2+ concentrations. Sr2+ uptake and Sr2+-dependent ATPase activity were concomitantly inhibited by sodium vanadate. In contrast to Ca2+, Sr2+ had no effect on Mg2+-dependent phosphoprotein formation. Taken together, these data indicate that Mg2+ stimulated Ca2+ and Sr2+ transport by increasing the Ca2+ (Sr2+)/ATP ratio.(ABSTRACT TRUNCATED AT 400 WORDS)     

Rat liver 3-hydroxy-3-methylglutaryl-CoA reductase. Catalysis of the reverse reaction and two half-reactions

Rat liver 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase catalyzes, in addition to its normal biosynthetic or forward reaction (HMG-CoA + 2 NADPH + 2H+----mevalonate + 2 NAD+ + CoASH), the reverse reaction (mevalonate + CoASH + 2 NADP+----HMG-CoA + 2 NADPH + 2H+) and two "half-reactions" that involve the presumed intermediate mevaldate (mevaldate + CoASH + NADP+----HMG-CoA + NADPH + H+ and mevaldate + NADPH + H+----mevalonate + NADP+). These reactions were studied using both enzyme solubilized by the traditional freeze-thaw method and enzyme solubilized with a nonionic detergent in the presence of inhibitors of proteolysis. All four reactions were inhibited by mevinolin, a known inhibitor of the forward (biosynthetic) reaction catalyzed by HMG-CoA reductase. When the enzyme was inactivated by ATP and a cytosolic, ADP-dependent HMG-CoA reductase kinase, the rates of both the forward reaction and the half-reactions decreased to comparable extents. Although coenzyme A is not a stoichiometric participant in the second half-reaction (mevaldate + NADPH + H+----mevalonate + NADP+), it was required as an activator of this reaction. This observation implies that coenzyme A may remain bound to the enzyme throughout the normal catalytic cycle of HMG-CoA reductase.     

Na+-Ca2+ exchange in squid optic nerve membrane vesicles is activated by internal calcium

The role of intracellular Ca2+ as essential activator of the Na+-Ca2+ exchange carrier was explored in membrane vesicles containing 67% right-side-out and 10% inside-out vesicles, isolated from squid optic nerves. Vesicles containing 100 microM free calcium exhibited a 2-fold increase in the initial rate of Na+i-dependent Ca2+ uptake as compared with vesicles where intravesicular calcium was chelated by 2 mM EGTA or 10 mM HEDTA. The activatory effect exerted by intravesicular Ca2+ on the reverse mode of Na+-Ca2+ exchange (i.e. Na+i-Ca2+o exchange) is saturated at about 100 microM Ca2+i and displays an apparent K 1/2 of 12 microM. Intravesicular Ca2+ produced activation of Na+i-Ca2+i exchange activity rather than an increase in Ca2+ uptake due to Ca2+-Ca2+ exchange. The presence of Ca2+i was essential for the Na+i-dependent Na+ influx, a partial reaction of the Na+-Ca2+ exchanger. In fact, the Na+ influx levels in vesicles loaded with 2 mM EGTA were close to those expected from diffusional leak while in vesicles containing Ca2+i an additional Na+-Na+ exchange was measured. The results suggest that in nerve membrane vesicles Ca2+ at the inner aspect of the membrane acts as an activator of the Na+-Ca2+ exchange system.     

Chromosomes of Phagocata kawakatsui and Bdellocephala annandalei from Lake Biwa-ko in Honshú, central Japan

Two lake-dwelling species of paludicolen triclads from Lake Biwa-ko (Honshû, Japan) were studied taxonomically and karyologically. (1) Phagocata kawakatsui Okugawa, 1956, is an epigean species usually inhabiting shallow springs and spring-fed streams in Central Japan. In Lake Biwa-ko, animals were obtained from several bottom stations of the littoral area in the southern part of the northern basin (3–70 m in depth). Chromosome numbers and karyotype: 2x=24 (2m+2sm+2sm+2m+2sm+2m+2sm+2m+2m+2sm+2m+2m). The first pair of metacentric chromosomes is very large in size. (2) Bdellocephala annandalei Ijima et Kaburaki, 1916, an endemic species, is distributed widely in the deep areas of the northern basin (30 to over 100 m in depth). Chromosome numbers and karyotype: 2x=28 (2m+2sm+2sm+2sm+2sm+2m+2m+2m+2m+2m+2m+2m+2m+2m) with the first pair of metacentric chromosomes very long.     

Fertilization acid release in Urechis eggs. II. The stoichiometry of Na+ uptake and H+ release

We tested the hypothesis that Na+ uptake and H+ release at fertilization of Urechis eggs might occur via a Na+:H+ exchange. Previous studies have shown that (1) Na+ uptake is proportional to the number of entering sperm in seawater with or without lowered Na+ and (2) H+ release is proportional to external pH. Therefore, to determine if Na+ uptake and H+ release are always proportional, we determined the effect of polyspermy on H+ release in natural and low Na+ seawater and the effect of external pH on Na+ uptake and release. Na+ uptake and H+ release do not covary in a manner consistent with a Na+:H+ exchange. H+ release under most conditions was manner consistent with a Na+:H+ exchange. H+ release under most conditions was independent of the number of sperm/egg and in low Na+ seawater was at most 53 +/- 16% of that in natural seawater. In contrast, Na+ uptake in low Na+ seawater can be more than in natural seawater (Jaffe et al., J. Gen. Physiol. 73, 469-492, 1979). In natural seawater Na+ uptake exceeded H+ release; at pH 7 Na+ uptake was 2 pmol/egg, but there was no H+ release. Since Na+ release did not increase at fertilization at pH 7, neither Na+:Na+ nor Na+:H+ exchange could account for the Na+ uptake. An alternate hypothesis is suggested: Na+ uptake is primarily via the channels responsible for the fertilization potential, while H+ release is by another route that is affected by the membrane potential during the fertilization potential.     

Digital imaging approaches for phenotyping whole plant nitrogen and phosphorus response in Bracbypodium distacbyon

This work evaluates the phenotypic response of the model grass （Brachypodium distacbyon （L.） P. Beauv.） to nitrogen and phosphorus nutrition using a combination of imaging techniques and destructive harvest of shoots and roots. Reference line Bd21-3 was grown in pots using 11 phosphorus and 11 nitrogen concentrations to establish a dose-response curve. Shoot biovolume and biomass, root length and biomass, and tissue phosphorus and nitrogen concentrations increased with nutrient concentration. Shoot biovolume, estimated by imaging, was highly correlated with dry weight （R2 〉 0.92） and both biovolume and growth rate responded strongly to nutrient availability. Higher nutrient supply increased nodal root length more than other root types. Photochemical efficiency was strongly reduced by low phosphorus concentrations as early as 1 week after germination, suggesting that this measurement may be suitable for high throughput screening of phosphorus response. In contrast, nitrogen concentration had little effect on photochemical efficiency. Changes in biovolume over time were used to compare growth rates of four accessions in response tonitrogen and phosphorus supply. We demonstrate that a time series image-based approach coupled with mathematical modeling provides higher resolution of genotypic response to nutrient supply than traditional destructive techniques and shows promise for high throughput screening and determina- tion of genomic regions associated with superior nutrient use efficiency.     

Age and ovarian development are related to worker personality and task allocation in the ant Leptothorax acervorum

In social insects, workers of different morphological castes and age are known to act differently. Yet, it is unclear how body size and ovarian development influence worker personalities （i.e. consistent behavioral variation） and task allocation in similar aged ant workers of monomorphic species. Behavioral variation is thought to be a key element of division of labor, but few studies have linked worker personality to task allocation. We investigated individual behavior in Leptothorax acervorum ant workers at two time points during the first three months of their life and in two different settings. We observed worker behavior in the nest （i.e. task allocation） and in standardized aggression, exploration and brood care experiments （i.e. personality） and found behavioral repeatability in foraging and exploration. Further, workers acted consistently across settings： workers with a more ag gressive and exploratory personality type were more active in the nest. Moreover, ovarian development was associated with worker personality and task allocation： older workers with welldeveloped ovaries foraged less, but were more aggressive and exploratory. In accordance with the typical agepolyethism of social insects, workers became more active and foraged more as they grew older. Consequently, our study suggests that task allocation in Leptothorax acervorum is not only influenced by ovari an development and age, but moreover by the personalities of its workers .     

Viral suppression of innate immunity via spatial isolation of TBK1/IKKε from mitochondrial antivirai platform

For antiviral signaling mediated by retinoic acid-inducible gene I （RiG-I）-like receptors （RLRs）, the recruitment of cytosoUc RLRs and downstream molecules （such as TBK1 and IKKε） to mitochondriaL platform is a central event that facilitates the establishment of host antiviral state. Here, we present an example of viral targeting for immune evasion through spatial isolation of TBK1/IKKε from mitochond riai antiviral platform, which was employed by severe fever with thrombocytopenia syndrome virus （SFTSV）, a deadly bunyavirus emerging recently. We showed that SFTSV nonstructural protein NSs functions as the interferon （IFN） antagonist, mainly via suppressing TBK1/IKKε-IRF3 signaling. NSs mediates the formation of cytoplasmic inclusion bodies （IBs）, and the blockage of IB formation impairs IFN-inhibiting activity of NSs. We next demonstrate that I Bs are utilized to compartmentalize TBK1/I KKε. The compartmentalization results in spatial isolation of the kinases from mitochondria, and deprived TBK1/IKKε may participate in antiviral complex assembly, leadingto the blockage of lFN ind uction. This study proposes a new role of viral I Bs as virus-built＇jail＇ for imprisoning cellular factors and presents a novel and likely common mechanism of viral immune evasion through spatial isolation of critical signaling molecules from the mitochondrial antiviral platform.     

The bottlenose dolphin Tursiops truncatus foraging around a fish farm：Effects of prey abundance on dolphins＇ behavior

The extent to which prey abundance influences both bottlenose dolphin foraging behavior and group size in the presence of human activities has not previously been studied.The primary aim of this study was to identify and quantify how wild bottlenose dolphins respond,individually and as groups,to the relative abundance of prey around a fish farm.Detailed views of dolphins＇ behavior were obtained by focal following individual animals whilst simultaneously collecting surface and underwater behavioral data.A total of 2150 dive intervals were analyzed,corresponding to 342 focal samples,lasting over 34 hours.Bottlenose dolphins remained submerged for a mean duration of 46.4 seconds and a maximum of 249 seconds.This study provides the first quantified data on bottlenose dolphin diving behavior in a marine fin-fish farm area.This study＇s results indicate that within a fish farm area used intensively by bottlenose dolphins for feeding,dolphins did not modify dive duration.Additionally,underwater observations confirmed that dolphins find it easier to exploit a concentrated food source and it appears that hunting tactic and not group size plays an important role during feeding activities.Thus,bottlenose dolphins appear capable of modifying their hunting tactics according to the abundance of prey.When top predators display behavioral responses to activities not directed at them,the task of studying all possible effects of human activities can become even more challenging.     

Characterization of Na+/Mg2+ antiport by simultaneous 28Mg2+ influx

During net Mg2+ efflux from Mg2+-preloaded chicken erythrocytes, which occurs via Na+/Mg2+ antiport, 28Mg2+ is taken up intracellularly. Km of 28Mg2+ influx amounted to 1 mM. In Na+-free medium Vmax of 28Mg2+ influx was increased and Km was reduced to 0.2 mM. 28Mg2+ influx was noncompetitively inhibited by amiloride as was found for Na+/Mg2+ antiport. The results indicate that, extracellularly, Mg2+ can compete with Na+ for common binding sites of the Na+/Mg2+ antiporter, resulting in 28Mg2+-24Mg2+ exchange. The rate of Mg2+ exchange depends on extracellular Na+ and on the rate of net Mg2+ efflux.     

Effects of diltiazem or verapamil on calcium uptake and release from chicken skeletal muscle sarcoplasmic reticulum

The purpose of this study was to determine the effects of 2 Ca2+ channel blockers, verapamil and diltiazem, on calcium loading (active Ca2+ uptake) and the following Ca2+ release induced by silver ion (Ag+) and Ca2+ from the membrane of heavy sarcoplasmic reticulum (SR) of chicken skeletal muscle. A fluorescent probe technique was employed to determine the calcium movement through the SR. Pretreatment of the medium with diltiazem and verapamil resulted in a significant decrease in the active Ca2+ uptake, with IC50 of about 290 micromol/L for verapamil and 260 micromol/L for diltiazem. Inhibition of Ca2+ uptake was not due to the development of a substantial drug-dependent leak of Ca2+ from the SR. It might, in part, have been mediated by a direct inhibitory effect of these drugs on the Ca2+ ATPase activity of the SR Ca2+ pump. We confirmed that Ca2+ channel blockers, administered after SR Ca2+ loading and before induction of Ca2+ release, caused a dose-dependent inhibition of both Ca2+- and Ag+-induced Ca2+ release rate. Moreover, if Ca2+ channel blockers were administered prior to SR Ca2+ loading, in spite of Ca2+ uptake inhibition the same reduction in Ca2+- and Ag+-induced Ca2+ release rate was seen. We showed that the inhibition of Ag+-induced Ca2+ release by L-channel blockers is more sensitive than Ca2+-induced Ca2+ release inhibition, so the IC50 for Ag+- and Ca2+-induced Ca2+ release was about 100 and 310 micromol/L for verapamil and 79 and 330 micromol/L for diltiazem, respectively. Our results support the evidence that Ca2+ channel blockers affect muscle microsome of chicken skeletal muscle by 2 independent mechanisms: first, reduction of Ca2+ uptake rate and Ca2+-ATPase activity inhibition, and second, inhibition of both Ag+- and Ca2+-induced Ca2+ release by Ca2+ release channels. These findings confirm the direct effect of Ca2+ channel blockers on calcium release channels. Our results suggest that even if the SR is incompletely preloaded with Ca2+ because of inhibition of Ca2+ uptake by verapamil and diltiazem, no impairment in Ca2+ release occurs.     

毛百合根尖染色体Giemsa C-带分析

本研究利用Giemsa C-带方法对毛百合(Lilium dahuricum Ker-Gawl)根尖染色体进行了分析。研究结果表明毛百合试管苗的染色体倍性变异丰富,染色体倍性变异包括二倍体(2n=2×=24)、三倍体(2n=3×=36)、四倍体(2n=4×=48)到六倍体(2n=6×=72)。对二倍体毛百合的C-带结果进行分析,其带型公式为:2n=2×=24=2CI++2CI+T+T++6I+2I++2I++2I+T++2I+T++2I+T++2T++2T+。每条染色体上都显示出显著的特征带,而且带纹的深浅差异明显。强带主要集中在长短臂上。因此,GiemsaC-带方法可以将毛百合(L.dahuricum)的每条染色体区分开。