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

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.