Integration of P2Y receptor-activated signal transduction pathways in G protein-dependent signalling networks

The role of nucleotides in intracellular energy provision and nucleic acid synthesis has been known for a long time. In the past decade, evidence has been presented that, in addition to these functions, nucleotides are also autocrine and paracrine messenger molecules that initiate and regulate a large number of biological processes. The actions of extracellular nucleotides are mediated by ionotropic P2X and metabotropic P2Y receptors, while hydrolysis by ecto-enzymes modulates the initial signal. An increasing number of studies have been performed to obtain information on the signal transduction pathways activated by nucleotide receptors. The development of specific and stable purinergic receptor agonists and antagonists with therapeutical potential largely contributed to the identification of receptors responsible for nucleotide-activated pathways. This article reviews the signal transduction pathways activated by P2Y receptors, the involved second messenger systems, GTPases and protein kinases, as well as recent findings concerning P2Y receptor signalling in C6 glioma cells. Besides vertical signal transduction, lateral cross-talks with pathways activated by other G protein-coupled receptors and growth factor receptors are discussed

MTF characterization of small pixel pitch IR cooled photodiodes Using EBIC

International audienceExperimental assessment of small pitch cooled infrared focal plane arrays (FPA) modulation transfer function (MTF) is becoming an important issue. Indeed, the pitch approaches the typical carrier diffusion length of minority carriers in the absorber material. Therefore, the MTF is an important figure of merit of those arrays as it may be degraded by lateral diffusion. Moreover, the pitch also approaches the sensed wavelength so direct MTF measurement using optical projections becomes difficult. In this paper, we propose the use of electron beam induced current to experimentally characterize the MTF of small pitch cooled FPAs. Practically, the device is mounted inside a scanning electron microscope onto a cooled sample stage. The diode area is then scanned by the electron beam instead of the optical beam in classical MTF measurement. Because of the very narrow electron beam, the MTF can then be estimated with an excellent precision. First scans of mid-wave 7.5 μm pitch HgCdTe diodes are shown, demonstrating a 55% MTF at the Nyquist frequency, consistent with 3D electro-optical modeling. The relevance of this estimation is also discussed, in comparison with classical projection methods