Osmotic behavior and transport properties of human islets in a dimethyl sulfoxide solution

The osmotic responses of isolated human islets were evaluated using a perfusion cryomicroscope device. Individual islet volumes were measured following equilibration with a series of solutions of graded solute concentration. The osmotically inactive volume for human islets was determined to be 25% from a Boyle-van't Hoff plot of these data. A network thermodynamic model was developed via the bond graph method to describe the transport of water and cryoprotective agent in pancreatic islets. The model was curve fit to transient volumetric data for the response of islets to a stepwise exposure to 1 Me2SO at temperatures of 24.0, 3.0, or -3.5 degrees C. Standard membrane transport parameters (Lp, omega, sigma) and interstitial diffusion transport properties (kappa w, kappa p) were calculated from the fitting procedure. The temperature coefficients for membrane transport properties were expressed in terms of activation energies for water (ELp) and Me2SO (E omega). Osmotic challenge experiments conducted with fresh and cryopreserved human islets indicate that frozen/thawed islets exhibit a a slight increase in transport properties.