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Department of Medical Cell Biology, Biomedicum, Uppsala University, 751 23 Uppsala, Sweden
The cytoplasmic
Ca2+ concentration
([Ca2+]i)
and insulin release were measured simultaneously in mouse pancreatic
islets cultured overnight.
[Ca2+]i
was 105 nM and insulin release 3 pmol · g
1 · s
1
at 3 mM glucose. An increase to 7 mM glucose reduced
[Ca2+]i
transiently, whereas insulin release doubled and was pulsatile with a
frequency of 0.47 min
1.
[Ca2+]i oscillations with similar frequency
appeared at 11 mM glucose associated with increased amplitude of the
insulin oscillations, raising the secretory rate 10-fold. In the
presence of 16 and 20 mM glucose
[Ca2+]i
was >300 nM and showed no oscillations apart from two islets, which
demonstrated
[Ca2+]i
oscillations with small amplitude at 16 mM glucose. Insulin release
with maintained frequency increased by 46 and 31%, respectively. When
the glucose concentration was increased from 3 to 11 mM, [Ca2+]i
decreased with a nadir that appeared significantly earlier than when
the glucose concentration was raised from 3 to 7 mM. Glucose-induced
insulin release from the isolated islet is pulsatile both at stable and
oscillatory
[Ca2+]i,
with changes in secretory rate caused by the sugar also when [Ca2+]i
is unchanged.
insulin secretion; cytoplasmic calcium concentration; oscillations; islets of Langerhans; endocrine pancreas
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