Measurements of the effective diffusion coefficient of oxygen in pancreatic islets

The effective diffusion coefficient of oxygen in pancreatic islets is an important parameter that is needed for the development of models of viability and function of pancreatic islets that are transplanted to cure diabetes, especially when encapsulated in devices. We have developed a method for estimating the maximum oxygen consumption rate (V-max) and the oxygen permeability in tissue (alpha D-t(t)) in a suspension of spherical aggregates of different sizes from measurements of the bulk oxygen partial pressure in batch oxygen consumption experiments. The method made use of a model of oxygen consumption and diffusion in the spheres and a parameter estimation scheme. Measurements made with three different batches of rat islets yielded batch averages of V-max = 3.40 +/- 0.77 x 10(-8) mol/(cm(3) s) and (alpha D-t(t) = 1.34 +/- 0.36 x 10(-14) mol/(cm mmHg s). Using a literature estimate for the solubility (alpha(t)) yields D-t = 1.31 +/- 0.36 x 10(-5) cm(2)/s at 37 degrees C. These oxygen permeability and diffusion coefficient values are similar to 38% and similar to 47% of their values in water, respectively.