Membranes of Tetrahymena II. Direct visualization of reversible transitions in biomembrane structure induced by temperature

Rapid temperature changes cause reversible structural transitions in the alveolar membranes of the poikilothermic eukaryote Tetrahymena as revealed by freeze-etch electron microscopy. At an optimal growth temperature of 28°C, 115-Å particles are randomly distributed on the outer faces of the fractured alveolar membranes and apparently corresponding holes are seen on the inner faces. After chilling the cells to 5°C, these particles and holes are largely aggregated. Reheating the cells to 28°C causes a random redistribution of particles and holes. This temperature-induced phenomenon of reversible particle aggregation is discussed with respect to movement of membrane components. We conclude that membrane components move translationally and/or normally to the membrane plane which may be important for transport processes within and across biomembranes.