| Abstract: | 1. The diffusion of the cryoprotective non-electrolyte dimethyl sulphoxide (DMSO) in the isolated guinea-pig taenia coli at 37, 25 and 0 degrees C has been studied using (35)S]DMSO.2. Within 1 hr after immersion at 37 degrees C in Krebs solution containing 20% (w/v) DMSO and trace amounts of (35)S]DMSO, the non-electrolyte was distributed uniformly throughout a volume equivalent to the total initial water content of the muscle.3. The kinetics of efflux of (35)S]DMSO from muscles at constant volume were analysed on the basis of two models: one incorporated radial diffusion in extracellular fluid with simultaneous permeation into the cells, the other involved only radial diffusion in homogeneous cylinders of tissue having no internal barriers to diffusion; the former was found to give a better representation of the efflux kinetics.4. If it was assumed that the rate of diffusion of DMSO in the extracellular space of taenia coli was the same as that in the bathing medium, the values of the extracellular space and the permeability of smooth muscle to DMSO, obtained from the analysis of the efflux kinetics, were 454 +/- 19 ml./kg and 2.36 +/- 0.05 x 10(-6) cm sec(-1) at 37 degrees C.5. The activation energy for the transfer of DMSO across the surface of the cell was estimated to be 6.0 kcal/mole at 37 degrees C, 6.6 kcal/mole at 25 degrees C and 11.6 kcal/mole at 0 degrees C, indicating either that the equivalent pore radius of the cells decreased with temperature or that the cell permeability represented the sum of two fluxes, one through the aqueous pores of the cell and the other through the lipid phase of the cell membrane, each with a different energy of activation.6. A net flux of water across the surface of the cells, superimposed on the efflux of DMSO, markedly affected the rate of diffusion of the non-electrolyte out of the whole tissue; however, it was considered that an analysis of the efflux kinetics was not possible under these conditions.7. These results provide a basis for methods which will be used to investigate the possibility of preserving tissue in unfrozen aqueous media at sub-zero temperatures. |
