A plant bioassay for determining the chronic phytotoxicity parameters of metal-contaminated soils and wastes

International audienc

Inositol 1,4,5-trisphosphatem and ryanodinemsensitive Ca2+ release channel-dependent Ca2+ signalling in rat portal vein myocytes

International audienc

Ca(2+) signals mediated by Ins(1,4,5)P(3)-gated channels in rat ureteric myocytes.

Localized Ca(2+)-release signals (puffs) and propagated Ca(2+) waves were characterized in rat ureteric myocytes by confocal microscopy. Ca(2+) puffs were evoked by photorelease of low concentrations of Ins(1,4,5)P(3) from a caged precursor and by low concentrations of acetylcholine; they were also observed spontaneously in Ca(2+)-overloaded myocytes. Ca(2+) puffs showed some variability in amplitude, time course and spatial spread, suggesting that Ins(1,4,5)P(3)-gated channels exist in clusters containing variable numbers of channels and that within these clusters a variable number of channels can be recruited. Immunodetection of Ins(1,4,5)P(3) receptors revealed the existence of several spots of fluorescence in the confocal cell sections, supporting the existence of clusters of Ins(1,4,5)P(3) receptors. Strong Ins(1,4,5)P(3) photorelease and high concentrations of acetylcholine induced Ca(2+) waves that originated from an initiation site and propagated in the whole cell by spatial recruitment of neighbouring Ca(2+)-release sites. Both Ca(2+) puffs and Ca(2+) waves were blocked selectively by intracellular applications of heparin and an anti-Ins(1,4,5)P(3)-receptor antibody, but were unaffected by ryanodine and intracellular application of an anti-ryanodine receptor antibody. mRNAs encoding for the three subtypes of Ins(1,4,5)P(3) receptor and subtype 3 of ryanodine receptor were detected in these myocytes, and the maximal binding capacity of [(3)H]Ins(1,4,5)P(3) was 10- to 12-fold higher than that of [(3)H]ryanodine. These results suggest that Ins(1,4,5)P(3)-gated channels mediate a continuum of Ca(2+) signalling in smooth-muscle cells expressing a high level of Ins(1,4,5)P(3) receptors and no subtypes 1 and 2 of ryanodine receptors

Calcium signalling through nucleotide receptor P2X1 in rat portal vein myocytes

ATP-mediated Ca2+ signalling was studied in freshly isolated rat portal vein myocytes by means of a laser confocal microscope and the patch-clamp technique.In vascular myocytes held at −60 mV, ATP induced a large inward current that was supported mainly by activation of P2X1 receptors, although other P2X receptor subtypes (P2X3, P2X4 and P2X5) were revealed by reverse transcription-polymerase chain reaction.Confocal Ca2+ measurements revealed that ATP-mediated Ca2+ responses started at initiation sites where spontaneous or triggered Ca2+ sparks were not detected, whereas membrane depolarizations triggered Ca2+ waves by repetitive activation of Ca2+ sparks from a single initiation site.ATP-mediated Ca2+ responses depended on Ca2+ influx through non-selective cation channels that activated, in turn, Ca2+ release from the intracellular store via ryanodine receptors (RYRs). Using specific antibodies directed against the RYR subtypes, we show that ATP-mediated Ca2+ release requires, at least, RYR2, but not RYR3.Our results suggest that, in vascular myocytes, Ca2+ influx through P2X1 receptors may trigger Ca2+-induced Ca2+ release at intracellular sites where RYRs are not clustered

Sphingolipids differentially regulate mitogen-activated protein kinases and intracellular Ca(2+) in vascular smooth muscle: effects on CREB activation

1. Related sphingolipids, sphingosine 1-phosphate (S1P) and sphingosylphosphorylcholine (SPC), have important effects on vascular smooth muscle. The aim of this study was to investigate the intracellular pathways regulated by S1P and SPC in rat cerebral artery. 2. In cerebral arteries, S1P increased extracellular signal-regulated kinase (ERK)1/2 phosphorylation (5.2±1.4-fold increase) but did not activate p38 mitogen-activated protein kinase (p38MAPK) as assessed by immunoblotting. In contrast, SPC increased p38MAPK phosphorylation (3.0±0.3-fold increase) but did not stimulate ERK1/2. This differential activation was confirmed by measuring activation of heat shock protein (HSP) 27, a known downstream target of p38MAPK. Only SPC, but not S1P, activated HSP27. 3. In enzymatically dispersed cerebral artery myocytes, SPC increased [Ca(2+)](i) in a concentration-dependent manner (peak response at 10 μM: 0.4±0.02 ratio units) as determined using the Ca(2+) indicator, Fura 2. In contrast to S1P, the SPC-induced [Ca(2+)](i) increase did not involve intracellular release but was due to Ca(2+) influx via L-type Ca(2+) channels. 4. Despite differences in signalling, both S1P and SPC phosphorylated the transcription factor cAMP response element-binding protein (CREB). S1P-induced CREB activation was dependent on ERK1/2 and Ca(2+)-calmodulin-dependent protein kinase (CaMK) activation. CREB activation by SPC required both p38MAPK and CaMK activation, but not ERK1/2. 5. In conclusion, S1P and SPC activate distinct MAP kinase isoforms and increase [Ca(2+)](i) via different mechanisms in rat cerebral artery. This does not affect the ability of S1P or SPC to activate CREB, although this occurs via different pathways

Evaluation des apports d'un biotest vegetal et de la speciation des elements traces a la mise au point d'une batterie de tests d'ecotoxicologie terrestre applicable aux sols et aux dechets Sous-theme : biotest vegetal

Available from INIST (FR), Document Supply Service, under shelf-number : RP 400 (1987) / INIST-CNRS - Institut de l'Information Scientifique et TechniqueSIGLEAgence de l'Environnement et de la Maitrise de l'Energie (ADEME),= 75 - Paris (France)FRFranc