WATER PERMEABILITY AND ITS ACTIVATION-ENERGY FOR INDIVIDUAL HAMSTER PANCREATIC-ISLET CELLS

Coupled with the rapid development of clinical pancreatic islet transp lantation, there is an increasing requirement for cryopreservation of viable islets. Fundamental cryobiology requires determination of sever al cryobiophysical parameters to predict optimal cryopreservation proc edures. These include water permeability or hydraulic conductivity (L( p)) and its activation energy (E(a)), the permeability of the cell pla sma membrane to a cryoprotectant(s) (P-s) and its E(a), the osmoticall y inactive fraction of cell volume (V-b), and the intracellular ice fo rmation temperature. For islet cells, these parameters have not previo usly been reported. In the present studies, the L(p), its E(a), and V- b were determined for isolated individual golden hamster pancreatic is let cells. The L(p) and V-b parameters were also measured for correspo nding exocrine cells. Both islet and the exocrine cells appeared to be ideal osmometers over the experimental range when examined by the Boy le Van't-Hoff relationship (linear regression, r = 0.99 for both types of cells). Extrapolation of these plots generated V-b values of 0.40 for the islet cells and 0.45 for the pancreatic exocrine cells. To det ermine the L(p), kinetic changes of cell volume over time (dv/dt) in r esponse to anisoosmotic conditions (ranging from 145 mOsm/kg to 1.35 O sm/kg) were measured using an electronic particle counter. The experim ental data were fitted to generate the L(p) values by least-squares cu rve fitting to a differential equation describing osmotic water moveme nt across the plasma membrane. For pancreatic islet cells, the L(p) wa s determined to be 0.25 +/- 0.03 mu m/min/atm ((X) over bar +/- SD, n = 14) at 22 degrees C, 0.54 +/- 0.07 (n = 10), 0.06 +/- 0.008 (n = 9), and 0.01 +/- 0.001 (n = 9) at 37, 8, and 0 degrees C, respectively. T he E(a) for L(p) was calculated from the slope of the Arrhenius plot b ased upon the mean L(p) values at the four different temperatures. The E(a) was 16.21 Kcal/mol between 0 and 37 degrees C. Based upon these values, an optimal cooling rate for cryopreserving pancreatic islet ce lls is predicted to be approximately 0.5 degrees C min. The L(p) for t he individual exocrine cells was determined to be 3.73 +/- 1.75 mu m/m in/atm (n = 13) al 22 degrees C, which was approximately 10 times the L(p) value of the corresponding islet cells. (C) 1995 Academic Press, Inc.