We investigate the time required for glucose to diffuse through an iso
lated pancreatic islet of Langerhans and reach an equilibrium. This qu
estion is relevant in the context of in vitro electrophysiological stu
dies of the response of an islet to step changes in the bath glucose c
oncentration. Islet cells are electrically coupled by gap junctions, s
o nonuniformities in islet glucose concentration may be reflected in t
he activity of cells on the islet periphery, where electrical recordin
gs 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 determi
nation of the equilibrium time is the transport of glucose into islet
beta-cells, which removes glucose from the interstitial spaces where d
iffusion occurs. This transport is incorporated by using a model of th
e GLUT-2 glucose transporter. We find that. several minutes are requir
ed for the islet to equilibrate to a 10 mM change in bath glucose, a t
ypical protocol in islet experiments. It is therefore likely that in e
lectrophysiological islet experiments the glucose distribution is nonu
niform for several minutes after a step change in bath glucose. The de
lay in glucose penetration to the inner portions of the islet may be a
major contributing Tractor to the 1-2-min delay in islet electrical a
ctivity typically observed after bath application of a stimulatory con
centration of glucose.