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Title
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Membrane-bound nucleoside diphosphate kinase-activity in atrial cells of frog, guinea-pig, and human
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Author
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Abstract
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| Muscarinic K+ channels in inside-out patches of atrial cells from guinea pig or rabbit can be activated by Mg2+-ATP in the absence of acetylcholine and GTP or GDP. The ATP-dependent activation involves a phosphorylation and is postulated to be due to the association of a membrane-bound nucleoside diphosphate kinase (NDPK) with the G protein G(K): direct phosphorylation of the G(K)-bound GDP into GTP, catalyzed by NDPK, would result in activation of the G protein and, hence, activation of the channels. The aim of this study was to identify the presence of NDPK activity in atrial membranes by investigating the phosphate transfer between tritium-labeled nucleotides. We show that frog, guinea pig, and human atrial membranes contain a substantial NDPK activity since they catalyze the conversion from [H-3]GDP+nucleoside triphosphate (NTP or NTP-gamma-S) to [H-3]GTP (or [H-3]GTP-gamma-S), from [H-3]ADP+NTP to [H-3]ATP, and from [H-3]GTP+nucleoside diphosphate (NDP) to [H-3]GDP. The phosphate transfer rates for the [H-3]GDP+ATP to [H-3]GTP conversion are 1.8, 0.5, and 2.4-mu-mol inorganic phosphate formation/mg per 10 minutes at 37-degrees-C in frog, guinea pig, and human, respectively. The order of substrate efficiency for different NTPs was ATP>ITP is-approximately-equal-to GTP>UTP>CTP, which parallels the efficiency of these nucleotides in their activation of the muscarinic K+ channels. Addition of other nucleotides blocked the transphosphorylation reaction, indicating that the NTP-NDP conversion mechanism is aspecific, as is expected for an NDPK-catalyzed reaction. In conclusion, the data support the concept of NDPK involvement in the atrial muscarinic signal transduction cascade. |
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Language
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English
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Source (journal)
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Circulation research / American Heart Association. - New York
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Publication
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New York
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1992
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ISSN
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0009-7330
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DOI
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10.1161/01.RES.71.4.808
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Volume/pages
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71
:4
(1992)
, p. 808-820
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ISI
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A1992JN85600008
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Full text (Publisher's DOI)
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