Fetal pancreatic islets release insulin poorly in response to glucose; however, the cellular mechanism for this is controversial. By using fura 2 to measure changes in the cytoplasmic free Ca2+ concentration ([Ca2+]i) in β-cells, we have examined islets from fetal, neonatal, and adult rats to determine the ability of glucose and other secretagogues to cause an increase in [Ca2+]i. The effects of glucose (20 mmol/l), glyceraldehyde (20 mmol/l), leucine (20 mmol/l), arginine (20 mmol/l), and the channel effectors glipizide (50 μmol/l), BAY K8644 (2 μmol/l), diazoxide (300 μmol/l), and verapamil (20 μmol/l) on changes in [Ca2+]i were studied. In both the fetal and the mature islet, glyceraldehyde, leucine, arginine, glipizide, and BAY K8644 caused an increase in [Ca2+]i. In mature islets, glucose also increased [Ca2+]i; however, in the fetal islet, glucose had no effect on [Ca2+]i. The stimulus-induced increases in [Ca2+]i in fetal and adult islets were both significantly inhibited by the addition of either diazoxide or verapamil. Similar results were obtained when insulin secretion was measured. Our data show that various secretagogues are able to stimulate fetal islets and cause an increase in [Ca2+]i. Glucose, however, fails to cause an increase in [Ca2+]i in the fetal islet. Hence, the immature insulin secretory response to glucose by the fetal islet is due to the inability of the fetal β-cell to translate glucose stimulation into the increase in [Ca2+]i required for exocytosis of the insulin granule.
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Original Articles|
January 01 1995
Insulin Secretagogues, But Not Glucose, Stimulate an Increase in [Ca2+]i in the Fetal Rat β-cell
Anthony J Weinhaus;
Anthony J Weinhaus
Departments of Medicine, University of Sydney
Sydney, Australia
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Philip Poronnik;
Philip Poronnik
Physiology, University of Sydney
Sydney, Australia
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David I Cook;
David I Cook
Physiology, University of Sydney
Sydney, Australia
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Bernard E Tuch
Bernard E Tuch
Department of Endocrinology, Prince of Wales Hospital
Sydney, Australia
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Address correspondence and reprint requests to Dr. Bernard E. Tuch, Department of Endocrinology, Prince of Wales Hospital, High St., Randwick, New South Wales 2031, Australia.
Diabetes 1995;44(1):118–124
Article history
Received:
April 21 1994
Revision Received:
October 06 1994
Accepted:
October 06 1994
PubMed:
7529202
Citation
Anthony J Weinhaus, Philip Poronnik, David I Cook, Bernard E Tuch; Insulin Secretagogues, But Not Glucose, Stimulate an Increase in [Ca2+]i in the Fetal Rat β-cell. Diabetes 1 January 1995; 44 (1): 118–124. https://doi.org/10.2337/diab.44.1.118
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