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  • Blackwell Publishing Ltd  (2)
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  • 1
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The human dopamine D2L (long form) and D2S (short form) receptors were expressed separately in mouse Ltk− fibroblast cells to investigate whether there is a difference in transmembrane signaling of these D2 receptors. Both receptors induced two signals, a phosphatidylinositol-linked mobilization of intracellular calcium and an inhibition of cyclic adenosine 3′-5’monophosphate (cAMP) accumulation, each with similar response magnitudes and identical pharmacology. Both calcium and cAMP signals were sensitive to pretreatment with pertussis toxin (PTX), indicating mediation by coupling to Gi/Go proteins. However, the two forms of D2 receptor were distinguished by acute prior activation of protein kinase C (PKC) with 12-O-tetradecanoyl 4β-phorbol 13-acetate (TPA): TPA blocked the D2S-mediated increase in cytosolic free calcium concentration ([Ca2+]i) in a concentration-dependent manner (between 10 nM and 1 μM), whereas the D2L receptor-induced increase in [Ca2+]i was resistant to TPA and was only partially (60%) inhibited by 100 μM TPA. By contrast, TPA did not alter the inhibition of cAMP accumulation induced by activation of either D2S or D2L receptors. We conclude that, in the L cell system, prior activation of PKC differentially modulates the transmembrane signaling of the D2L and D2S receptors, preferentially inhibiting the D2S receptor-mediated calcium signal but not altering the dopamine-induced inhibitory cAMP signal of either receptor subtype.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Neurokinin-1 (NK-1)/substance P (SP) receptors were solubilized using 10 mM 3-[(cholamidopropyl)-dimethylammonio]-1-propanesulfate from porcine striatal membranes (solubilization yield, 80%). In solubilized preparations, [3H]SP apparently bound to a single class of high-affinity sites (KD= 0.82 ± 0.13 nM) as in membrane ho-mogenates. The ligand selectivity pattern observed in both membrane and solubilized receptor preparations indicated that [Sar9, Met(O2)11]SP = SP ± senktide = [Nle10]neurokinin A4–10.This suggests the selective labeling of the NK-1 receptor class in both assays. Solubilized receptors were retained on agarose-coupled lectins that bind N-acetylglucosamine-galactose and β-galactose (Ricinus communis I and Ricinus communis II), mannose (concanavalin A and lentil), and N- acetylglucosamine (wheat germ agglutinin) but not on lectins binding fucose (Lotus A) and N-acetylgalactosamine (Dolichos biflorus A). Thus, it appears that porcine brain NK-1/SP receptors are enriched with various carbohydrate moieties, β-galactose and N-acetylglucosamine-galactose residues being especially abundant. This situation is rather different from that in various other members of the rhodopsin seven-trans-membrane receptor superfamily.
    Type of Medium: Electronic Resource
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