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Modulation of active Ca2+ uptake by the islet-cell endoplasmic reticulum
The Biochemical Journal
|April 15, 1983
Summary
Cytosol factors, not calmodulin or cyclic AMP, significantly enhance islet cell endoplasmic reticulum calcium uptake. This suggests a key role for these unidentified factors in regulating beta-cell calcium levels.
Area of Science:
- Cellular Biology
- Endocrinology
- Biochemistry
Background:
- Islet beta-cells regulate blood glucose via insulin secretion, a process dependent on intracellular calcium (Ca2+).
- The endoplasmic reticulum (ER) is a major intracellular Ca2+ store, and its uptake mechanisms are crucial for maintaining cellular Ca2+ homeostasis.
Purpose of the Study:
- To investigate the effects of calmodulin and cyclic AMP on active Ca2+ uptake by islet-cell ER.
- To identify potential regulators of Ca2+ transport in pancreatic beta-cells.
Main Methods:
- Assessed active Ca2+ uptake rates and ER filling capacity in isolated islet-cell ER fractions.
- Measured Ca2+-stimulated ATPase activity.
- Investigated the impact of cytosol fractions on Ca2+ uptake.
Main Results:
- Neither calmodulin nor cyclic AMP influenced Ca2+ uptake rate or ER filling capacity.
- A previously unidentified factor(s) present in the cytosol significantly increased both the rate and capacity of Ca2+ uptake by the ER.
- Calmodulin did not activate the associated Ca2+-stimulated ATPase activity.
Conclusions:
- The endoplasmic reticulum plays a significant role in controlling beta-cell Ca2+ concentrations.
- Unidentified cytosolic factors are potent regulators of ER Ca2+ uptake, suggesting a novel mechanism for controlling beta-cell function.