RESUMO
We have conceived, built, and operated a cryogenic vacuum valve with opening and closing times as short as 50 ms that can be used in strong magnetic fields and across a broad range of duty cycles. It is used to seal a cryogenic Penning trap at liquid-helium temperature for long-term storage of highly charged ions in a vacuum better than 10-15 hPa from a room-temperature ion beamline at vacuum conditions around 10-9 hPa. It will significantly improve any experiment where a volume at the most extreme vacuum conditions must be temporarily connected to a less demanding vacuum during repeated experimental cycles. We describe the design of this valve and show measurements that characterize its main features.
RESUMO
Expression of a variety of ABC efflux pumps including certain conjugate transporters of the multidrug resistance protein (MRP) subfamily is inducible in primate and rodent tissues, and in a variety of cell lines and primary cells in culture. In human cell lines (HepG2, MCF-7), we studied the inducibility of MRPs 1-5. Similar to the rat mrp2 gene, human mrp2 is inducible by the chemical carcinogen 2-AAF, the chemotherapeutic drug cisplatin and the barbiturate phenobarbital, as demonstrated in Northern and Western Blots. Furthermore, the antibiotic rifampicin was identified as MRP2 inducer in HepG2 cells. MRP1 and 4 mRNAs being expressed in human liver at a very low level could not be detected in HepG2 cells after treatment with various agents. However, MRP3 and 5 mRNAs were detected in addition to MRP2 and their expression was found to be increased by 2-AAF, cisplatin and rifampicin. MRP1 expression was studied in MCF-7 cells where the chemotherapeutic drug vinblastine and tert-butyl hydroquinone but not the MRP2 inducing agents described above acted as inducers.