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

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Abstract
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.