269 research outputs found
On LeĆniewskiâs Characteristica Universalis
LeĆniewski's systems deviate greatly from standard logic in some basic features. The deviant aspects are rather well known, and often cited among the reasons why LeĆniewski's work enjoys little recognition. This paper is an attempt to explain why those aspects should be there at all. LeĆniewski built his systems inspired by a dream close to Leibniz's characteristica universalis: a perfect system of deductive theories encoding our knowledge of the world, based on a perfect language. My main claim is that LeĆniewski built his characteristica universalis following the conditions of de Jong and Betti's Classical Model of Science (2008) to an astounding degree. While showing this I give an overview of the architecture of LeĆniewski's systems and of their fundamental characteristics. I suggest among others that the aesthetic constraints LeĆniewski put on axioms and primitive terms have epistemological relevance. © The Author(s) 2008
Ars experimentandi et conjectandi. Laws of Nature, Material Objects, and Contingent Circumstances
Oocyte expression with injection of purified T7 RNA polymerase.
International audienceThe Xenopus oocyte is a widely used system for protein expression. Investigators have had the choice between two different techniques: injection into the cytoplasm of in vitro transcribed complementary RNA (cRNA) or injection into the nucleus of complementary DNA (cDNA). We report on a third expression technique that is based on the combined injection of cDNA and purified T7 RNA polymerase directly into the cytoplasm of oocytes
A novel fast mechanism for GPCR-mediated signal transductionâcontrol of neurotransmitter release
In addition to calcium influx, charge movement in the G proteinâcoupled M2-muscarinic receptor is required for the control of acetylcholine release
High Extracellular Ca2+ Stimulates Ca2+-Activated Clâ Currents in Frog Parathyroid Cells through the Mediation of Arachidonic Acid Cascade
Elevation of extracellular Ca2+ concentration induces intracellular Ca2+ signaling in parathyroid cells. The response is due to stimulation of the phospholipase C/Ca2+ pathways, but the direct mechanism responsible for the rise of intracellular Ca2+ concentration has remained elusive. Here, we describe the electrophysiological property associated with intracellular Ca2+ signaling in frog parathyroid cells and show that Ca2+-activated Clâ channels are activated by intracellular Ca2+ increase through an inositol 1,4,5-trisphophate (IP3)-independent pathway. High extracellular Ca2+ induced an outwardly-rectifying conductance in a dose-dependent manner (EC50âŒ6 mM). The conductance was composed of an instantaneous time-independent component and a slowly activating time-dependent component and displayed a deactivating inward tail current. Extracellular Ca2+-induced and Ca2+ dialysis-induced currents reversed at the equilibrium potential of Clâ and were inhibited by niflumic acid (a specific blocker of Ca2+-activated Clâ channel). Gramicidin-perforated whole-cell recording displayed the shift of the reversal potential in extracellular Ca2+-induced current, suggesting the change of intracellular Clâ concentration in a few minutes. Extracellular Ca2+-induced currents displayed a moderate dependency on guanosine triphosphate (GTP). All blockers for phospholipase C, diacylglycerol (DAG) lipase, monoacylglycerol (MAG) lipase and lipoxygenase inhibited extracellular Ca2+-induced current. IP3 dialysis failed to induce conductance increase, but 2-arachidonoylglycerol (2-AG), arachidonic acid and 12S-hydroperoxy-5Z,8Z,10E,14Z-eicosatetraenoic acid (12(S)-HPETE) dialysis increased the conductance identical to extracellular Ca2+-induced conductance. These results indicate that high extracellular Ca2+ raises intracellular Ca2+ concentration through the DAG lipase/lipoxygenase pathway, resulting in the activation of Clâ conductance
Vigotski e a perspectiva enunciativa da relação entre linguagem, cognição e mundo social
- âŠ