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Journal of Neuroscience, Vol 6, 3128-3132, Copyright © 1986 by Society for Neuroscience
Somatostatin, an inhibitor of ACTH secretion, decreases cytosolic free calcium and voltage-dependent calcium current in a pituitary cell line
A Luini, D Lewis, S Guild, G Schofield and F Weight
Somatostatin is a neurohormone peptide that inhibits a variety of secretory
responses in different cell types. We have investigated the effects of
somatostatin on calcium current and intracellular free calcium in AtT-20
cells, a pituitary tumor line in which the inhibitory actions of this
peptide have been well characterized. At concentrations similar to those
that inhibit adrenocorticotropic hormone (ACTH) release, somatostatin and
its analogs reduced the levels of intracellular free calcium (as measured
by the Quin-2 technique). Nifedipine and other blockers of
voltage-dependent calcium channels also reduced cytosolic calcium levels.
The effects of somatostatin and nifedipine were not additive, suggesting
that somatostatin might inhibit calcium channels. Experiments using the
whole-cell patch-clamp technique showed that somatostatin reduces
voltage-dependent calcium current. The effects of somatostatin on cytosolic
calcium and calcium current appear to be independent of its ability to
reduce secretagogue- stimulated cAMP accumulation in these cells. We
propose that the somatostatin-induced decrease in cytosolic calcium
concentrations and the voltage-dependent calcium current are one of the
mechanisms by which somatostatin suppresses ACTH release in AtT-20 cells.
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