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Effect of secretagogues on cytosolic free Ca2+ and insulin release at different extracellular Ca2+ concentrations in the hamster clonal beta-cell line HIT-T15.

Abstract：

:We have examined the relationship between extracellular Ca2+, cytosolic free Ca2+ and insulin release in the clonal beta-cell line HIT-T15. Glucose-stimulated insulin release was dependent on the extracellular Ca2+ concentration in a dose-related manner; the threshold medium Ca2+ concentration for glucose-stimulated insulin release was 0.5 mM. Both forskolin and 12-O-tetradecanoylphorbol 13-acetate (TPA) increased insulin release in the presence of glucose at all extracellular Ca2+ concentration tested (0.1-2.5 mM) but not in the absence of Ca2+. Thus, the threshold medium Ca2+ concentration for glucose-stimulated insulin release was reduced to 0.1 mM by forskolin or TPA. Step-wise increases in the medium Ca2+ concentration in the presence of an initiator of insulin release resulted in a dose-related increase in cytosolic free Ca2+. In the presence of 10 mM glucose, cytosolic free Ca2+ in HIT cells was increased from 60 +/- 5 nM in Ca2+-free medium to 290 +/- 46 nM in medium containing 2.5 mM Ca2+. The effects of increasing extracellular Ca2+ in the presence of 40 mM K+ were similar but considerably more pronounced. Inclusion of either TPA or forskolin in the incubation medium had no significant effect on the steady-state cytosolic free Ca2+ levels in the absence of glucose but in the presence of 10 mM glucose forskolin caused modest (11-18%) increases in steady-state cytosolic free Ca2+ levels at extracellular Ca2+ concentrations of 0.25 mM or above. In contrast, in the presence of glucose TPA significantly reduced the steady-state levels of cytosolic free Ca2+ by 17-21% at extracellular Ca2+ concentrations of 0.25 mM or above. These data provide further evidence that insulin release mediated by activation of beta-cell protein kinases involves primarily an increase in sensitivity of the secretory system to intracellular Ca2+.

journal_name

Mol Cell Endocrinol

journal_title

Molecular and cellular endocrinology

authors

Hughes SJ,Chalk JG,Ashcroft SJ

doi

10.1016/0303-7207(89)90162-7

subject

Has Abstract

pub_date

1989-08-01 00:00:00

pages

35-41

issue

1-2

eissn

0303-7207

issn

1872-8057

journal_volume

pub_type

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Effect of secretagogues on cytosolic free Ca2+ and insulin release at different extracellular Ca2+ concentrations in the hamster clonal beta-cell line HIT-T15.