In:
Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 75, No. 5 ( 1978-05), p. 2234-2238
Abstract:
Isolated rat hepatocytes do not actively accumulate Ca 2+ during prolonged incubation in vitro ; however, these cells do exhibit a limited exchange of intracellular with extracellular Ca 2+ . The exchangeable pool represents about 2 nmol of Ca 2+ per mg of protein. In medium containing either a low (20 μM) or high (1 mM) concentration of Ca 2+ , the divalent cation ionophore, A23187 (at concentrations of 0.03-0.1 nmol/mg of protein), causes release of 45 Ca 2+ from this exchangeable pool but does not allow net influx of extracellular Ca 2+ detectable by the use of a Ca 2+ -sensitive electrode. Like A23187, the hormones norepinephrine, vasopressin, and glucagon (at concentrations that stimulate gluconeogenesis) each induces a similar net efflux of Ca 2+ . Treatment with one hormone decreases the subsequent reponse to the others, whereas treatment with A23187 abolishes the hormonal effects upon both Ca 2+ release and gluconeogenesis. The action of norepinephrine, but not of glucagon, upon Ca 2+ efflux is prevented by the α-adrenergic antagonist, phenoxybenzamine. The action of norepinephrine is not prevented by the β-adrenergic antagonist, propranolol. Together these results indicate that the release of Ca 2+ from a common pool of exchangeable Ca 2+ is important to the action of a variety of hormones on hepatocytes. This Ca 2+ pool in the isolated hepatocyte is characterized as being similar in size and having exchange kinetics that are comparable to those reported for the major intracellular pool of Ca 2+ in the intact liver. The possibility that this pool is intramitochondrial calcium is discussed.
Type of Medium:
Online Resource
ISSN:
0027-8424
,
1091-6490
DOI:
10.1073/pnas.75.5.2234
Language:
English
Publisher:
Proceedings of the National Academy of Sciences
Publication Date:
1978
detail.hit.zdb_id:
209104-5
detail.hit.zdb_id:
1461794-8
SSG:
11
SSG:
12
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