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Biophys. J. BioFAST: First Published October 1, 2004. doi:10.1529/biophysj.104.050955
© 2004 by the Biophysical Society.

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BIOPHYSICAL THEORY AND MODELING

Filtering of Calcium Transients by the Endoplasmic Reticulum in Pancreatic {beta}-Cells

Richard Bertram 1* and Arthur Sherman 2

1 Florida State University
2 National Institutes of Health

* To whom correspondence should be addressed. E-mail: bertram{at}sb.fsu.edu.

Submitted on August 4, 2004
Revised on September 5, 2004
Accepted on 23 September 2004


  Abstract
Calcium handling in pancreatic {beta}-cells is important for intracellular signaling, the control of electrical activity, and insulin secretion. The endoplasmic reticulum (ER) is a key organelle involved in the storage and release of intracellular calcium. Using mathematical modeling, we analyze the filtering properties of the ER and clarify the dual role that it plays as both a calcium source and a calcium sink. We demonstrate that recent time-dependent data on the free calcium concentration in pancreatic islets and {beta}-cell clusters can be explained with a model that uses a passive ER that takes up calcium when the cell is depolarized and the cytosolic calcium is elevated, and releases calcium when the cell is repolarized and the cytosolic calcium is at a lower concentration. We find that calcium-induced calcium release (CICR) is not necessary to explain the data, and indeed the model is inconsistent with the data if CICR is a dominating factor. Finally, we show that a three-compartment model that includes a "subspace compartment" between the ER and the plasma membrane provides the best agreement with the experimental calcium data.

Key Words: insulin secretion, islet of Langerhans




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Copyright © 2004 by the Biophysical Society.