Water permeability of mammalian cells as a function of temperature in the presence of dimethylsulfoxide: Correlation with the state of the membrane lipids

The water permeability of V-79 Chinese hamster lung fibroblasts was determined by measuring the rate of cell shrinkage in hypertonic medium using a cell sizer. The water permeability appears to follow Arrhenius kinetics as a function of temperature with a sharp discontinuity at 21°C. An activation energy of 7.0±1.6 kcal/mole was found below 21°C and 22.8±3.1 kcal/mole above 21°C. The correlation time of rotation of the spin label 2,2-dimethyl-5-dodecyl-5-methyloxazolidine-N-oxide was measured as a function of temperature in the cellular membranes, and shows a break at 20°C. A discontinuity was also found in the membrane to water partitioning of the spin label 2,2-dimethyl-5-pentyl-5-butyloxazolidine-N-oxide near 20°C. These breaks may correspond to a membrane lipid phase transition. Dimethylsulfoxide, in the concentration range of 0.2–0.5 M, decreases the water permeability by a factor of two.