Extracellular ATP, ADP and GTP increased the intracellular free Ca2+ concentration ([Ca2+]i) in a suspension of isolated rat hepatocytes. The [Ca2+]i was determined by measuring fura-2 fluorescence, and its increase was biphasic. The initial transient rise was followed by a longer-lasting plateau. The peak of the early component preceded the plateau level of the second component. A time course of change in [Ca2+]i in single cells at 100 microM-ATP was very similar to that observed in the suspension system. Preincubation of hepatocytes with 40 mM-caffeine, 2 mM-oxalate or 60 microM-dantrolene sodium inhibited the P2 purinergic response. The plateau phase was not observed when measured in the presence of extracellular 100 microM-LaCl3 or in the absence of extracellular Ca2+. The distribution of [Ca2+]i in single hepatocytes was also determined by fluorescence image analysis. In the initial phase, the increase in [Ca2+]i is greater in the peripheral region than the central region of the cell. Degradation of extracellular ATP by ecto-ATPase in the hepatocyte suspension was measured; the amount of ATP degradation was less than 10-15% of the initial amount (100 microM) during the measurement of the intracellular [Ca2+]i in the cell suspension. Extracellular ATP stimulated glucose synthesis. The rate of glucose production also showed two components, the initial fast component within 1 min and the subsequent slower component. The rate of the initial fast component did not depend on the presence or absence of extracellular Ca2+, whereas the rate of the subsequent component depended on it. The present study shows that the initial transient rise in [Ca2+]i plays an important role in triggering the gluconeogenesis.
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April 1992
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Research Article|
April 01 1992
Gluconeogenesis stimulated by extracellular ATP is triggered by the initial increase in the intracellular Ca2+ concentration of the periphery of hepatocytes
M Koike;
M Koike
1Faculty of Pharmaceutical Sciences, Toyama Medical and Pharmaceutical University, Toyama, 930-01 Japan
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T Kashiwagura;
T Kashiwagura
1Faculty of Pharmaceutical Sciences, Toyama Medical and Pharmaceutical University, Toyama, 930-01 Japan
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N Takeguchi
N Takeguchi
1Faculty of Pharmaceutical Sciences, Toyama Medical and Pharmaceutical University, Toyama, 930-01 Japan
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Publisher: Portland Press Ltd
Online ISSN: 1470-8728
Print ISSN: 0264-6021
© 1992 The Biochemical Society, London
1992
Biochem J (1992) 283 (1): 265–272.
Citation
M Koike, T Kashiwagura, N Takeguchi; Gluconeogenesis stimulated by extracellular ATP is triggered by the initial increase in the intracellular Ca2+ concentration of the periphery of hepatocytes. Biochem J 1 April 1992; 283 (1): 265–272. doi: https://doi.org/10.1042/bj2830265
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