Xenopus oocyte

Heterologous expression systems comprise prokaryotic organisms (e.g., E. coli) and eukaryotic cells (e.g., yeast, HEK293, Xenopus oocytes), which are used to functionally express foreign genes or cDNAs. 

This minimal K+ channel (MinK) encoded by KCNEl consists of 130 amino acid residues and has a single transmembrane segment. A slowly activating K+ current-induced MinK cRNA is expressed in Xenopus oocytes. Coexpression of KvLQTl with MinK induced a current that has characteristics similar to cardiac slowly activating delayed-rectifier K+ current, DCS, in contrast to DCR that has relative fast activation and is composed of hERG/MiRPl. 

Mouse Xenopus oocyte Activation of Ca2+-dependent Cl conductance NT SR 48692 Levocabastine ... 

The exact subunit composition of the Low Voltage-activated (LVA) Ca2+ channels is unknown [3,6]. Three ai subunits, Cav3.x, have been identified which induce large T-type current after expression in Xenopus oocytes and in HEK cells in the absence of additional subunits. The T-type current can be affected by the a2S and the y6 subunit suggesting a maximal subunit composition of oq/o S./y. 

The nicotinic acetylcholine (nACh) receptor also displays sensitivity to inhalants (Bale et al. 2002). To varying degrees, toluene appeared to antagonize the function of nACh receptors that comprise different subunits. At concentrations of 50 pM to 10 mM, toluene produced a reversible, concentration-dependent inhibition of acetylcholine-induced current in Xenopus oocytes expressing various nicotinic receptor subtypes, with the ol — 2 d ct3—P2 subunit combinations being more sensitive to inhibition than other receptor... 

Similar to alcohol (Lovinger and White 1991) and volatile anesthetics (Machu and Harris 1994), trichoroethane, trichloroethylene, and toluene enhance 5-HT3 receptor function. All three inhalants significantly and reversibly potentiated, in a dose-dependent manner, 5-HT-activated currents, mediated by mouse 5-HT3 receptors expressed in Xenopus oocytes. Another feature common to these drugs is that the acute use of inhalants, as well as alcohol and volatile anesthetics, can produce nausea and vomiting (Meredith et al. 1989). It is believed that 5-HT3 receptors located in the area postrema mediate this action of alcohol and the volatile anesthetics (Aapro 1991). 

Cruz SE, Mirshahi T, Thomas B, et al Effects of the abused solvent toluene on recombinant N-methyl-D-aspartate and non-N-methyl-D-aspartate receptors expressed in Xenopus oocytes. J Pharmacol Exp Ther 286 334-340, 1998 De Rosa E, Bartolucci GB, Sigon M, et al Hippuric acid and ortho-cresol as biological indicators ofoccupational exposure to toluene. Am J Ind Med 11 529—537,1987 Delteil P, Stoesser F, Stoesser R L theromanie. Ann Med Psychol (Paris) 1 329-340, 1974... 

Unity resulted in 4234 hits. After application of several filters and clustering of the remaining 1975 molecules, compounds from 18 of the 27 clusters were screened in Xenopus oocytes. One compound with an IC50 of 5.6pM belonged to a new class of Kvl.5 blockers and exhibited a favorable pharmacokinetic profile. After further optimization, compound 73 (IC50 = 0.7pM Fig. 16.9) resulted, with good oral bioavailability in rats [145]. 

Expression studies in Xenopus oocytes or transfected cell lines originally suggested that functional GABA-activated chloride channels could be formed by receptor subunits of each class in isolation. However, much better expression occurs with two or more subunit types in combination and it is likely that most native receptors contain at least three different subunits. Co-expression of a and /I subunits results in the assembly of... 

The DNA for the GABAA-receptor channel has been translated to the respective RNA by in vitro transcription of the cDNAs (for a and P) inserted into plasmids. The two RNAs, when injected together into Xenopus oocytes, produced GABA-sensitive CP-currents [3]. 

The molecular analysis of the Sh K channel transcription unit indicated that at least ten different channel subunits may be expressed in Drosophila cells. This observation raised a number of important questions only some of them can be addressed here. Each subunit has been expressed in the Xenopus oocyte expression system [11,12,29,39]. These experiments indicate that each subunit expresses distinct... 

Other recent and very compelling evidence that the P subunit may also be necessary for full activity [83] comes from the study of a high threshold but DHP-insen-sitive brain channel that has an a 1-like channel core. The cDNA for this brain channel was recently isolated and the mRNA was expressed in Xenopus oocytes. The current corresponding to this channel was increased when the mRNA for either the skeletal muscle 0.2 or P subunits were co-injected. However, when the brain ai-like mRNA was co-expressed with the combination of the skeletal muscle 2 and p mRNAs, the current was dramatically increased from 31 nA for the brain ai alone to 6 500nA for the combination [83]. These striking results are the best evidence so far obtained that the P subunit has a functional role in channel activity. Although these data were obtained with a DHP-insensitive channel, they pro-... 

Observations from various systems, including yeast, suggest that phosphorylation and dephosphorylation of proteins play important roles in the mitotic and meiotic cell cycles and the differentiation of germ cells. Extracts from mitotic HeLa cells contained phosphoproteins also present in other mitotic and meiotic cell types, but not in interphase cells (Davis et al., 1983). Exposure of Xenopus oocytes to progesterone results in a burst of protein phosphorylation shortly before GVBD (Mailer et al.,... 

Other phosphatases have also been identified and may be implicated in mitotic and meiotic germ cell functions. For example, INH was originally isolated from a Xenopus oocyte cell free system as an inhibitor of pre-MPF activity (Cyert and Kirschner, 1988). INH encodes a protein phosphatase 2Athat negatively regulates MPF activity by dephosphory-lating Cdc2 on thr-161 (Lee et al., 1991 Solomon et al., 1990). 

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