Membrane‐Bound Nucleoside Diphosphate Kinase Activity in Atrial Cells of Frog, Guinea Pig, and Human
作者:
Hein Heidbuchel,
Geert Callewaert,
Johan Vereecke,
Edward Carmeliet,
期刊:
Circulation Research
(OVID Available online 1992)
卷期:
Volume 71,
issue 4
页码: 808-820
ISSN:0009-7330
年代: 1992
出版商: OVID
关键词: acetylcholine;muscarinic K+channels;nucleoside diphosphate kinase;EC 2.7.4.6;G proteins
数据来源: OVID
摘要:
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 GK: direct phosphorylation of the GK-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 [3H]GDP+nucleoside triphosphate (NTP or NTPγS) to [3H]GTP (or [3H]GTPγS), from [3H]ADP+NTP to [3H]ATP, and from [3H]GTP+nucleoside diphosphate (NDP) to [3H]GDP. The phosphate transfer rates for the [3H]GDP+ATP to [3H]GTP conversion are 1.8, 0.5, and 2.4 μmol inorganic phosphate formation/mg per 10 minutes at 37°C in frog, guinea pig, and human, respectively. The order of substrate efficiency for different NTPs was ATP>ITP≅GTP>UTP>CTP, which parallels the effliciency 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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