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Copyright © 1998 The Biophysical Society. All rights reserved.
Biophysical Journal, Volume 74, Issue 4, 1722-1731, 1 April 1998
doi:10.1016/S0006-3495(98)77883-X
Glucose Diffusion in Pancreatic Islets of Langerhans
Richard Bertram*, 
, 
and Mark Pernarowski#
* School of Science, Pennsylvania State University, Erie, Pennsylvania 16563 USA
# Department of Mathematical Sciences, Montana State University, Bozeman, Montana 59717 USA
Address reprint requests to Dr. Richard Bertram, School of Science, Pennsylvania State University, Erie, PA 16563. Tel.: 814-898-6090; Fax: 814-898-6213.Abstract
We investigate the time required for glucose to diffuse through an isolated pancreatic islet of Langerhans and reach an equilibrium. This question is relevant in the context of in vitro electrophysiological studies of the response of an islet to step changes in the bath glucose concentration. Islet cells are electrically coupled by gap junctions, so nonuniformities in islet glucose concentration may be reflected in the activity of cells on the islet periphery, where electrical recordings are made. Using a mathematical model of hindered glucose diffusion, we investigate the effects of the islet porosity and the permeability of a surrounding layer of acinar cells. A major factor in the determination of the equilibrium time is the transport of glucose into islet β-cells, which removes glucose from the interstitial spaces where diffusion occurs. This transport is incorporated by using a model of the GLUT-2 glucose transporter. We find that several minutes are required for the islet to equilibrate to a 10mM change in bath glucose, a typical protocol in islet experiments. It is therefore likely that in electrophysiological islet experiments the glucose distribution is nonuniform for several minutes after a step change in bath glucose. The delay in glucose penetration to the inner portions of the islet may be a major contributing factor to the 1–2-min delay in islet electrical activity typically observed after bath application of a stimulatory concentration of glucose.
