Talk Abstract
The Sodium/Calcium Exchanger Affects the Plateau Fraction in Models for Electrical Bursting in Pancreatic -cells

Joint work with David Gall.

The glucose-stimulated secretion of insulin from -cells in pancreatic islets is induced by bursting electrical activity, consisting of a periodic alternation of active and silent phases. The modulation of the plateau fraction (fraction of time spent in the active phase) is an essential factor in the regulation of insulin release (Meissner, H.P. and H. Schmelz, 1974).

The Na⁺/Ca²⁺ exchanger is a Ca²⁺-activated electrogenic Ca²⁺-transporter of the plasma membrane of the pancreatic -cells (Gall, D. et al., 1999). We have incorporated the Na⁺/Ca²⁺ exchange in different single-cell models (Sherman, A., 1996) to investigate its role on electrical bursting behavior and insulin secretion. We show that the depolarizing influence of the Na⁺/Ca²⁺ exchange current is able to prolong the burst duration and increase the plateau fraction. In addition, the Na⁺/Ca²⁺ exchange can provide a physiological mechanism, among others like K(ATP) channels, to increase the plateau fraction as the glucose concentration is raised.

Gall, D., J. Gromada, I. Susa, A. Herchuelz, P. Rorsman, and K. Bokvist. Significance of Na/Ca-exchange for Ca²⁺-buffering and electrical activity in mouse pancreatic -cells. {\it Biophysical. J.}, in press.

\noindent Meissner, H.P. and H. Schmelz. Membrane potential of -cells in pancreatic islets. {\it Pfl\"ugers Arch.}, 351:195-206, 1974.

Sherman, A. Contributions of modeling to understanding stimulus-secretion coupling in pancreatic -cells. {\it Am. J. of Phys.}, 271: E362-E372, 1996.

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1998-1999 Mathematics in Biology