Adaptation of mouse leukemic cells (L5178Y) to anisotonic media : II. Cell growth

Mouse lymphoma cells (L5178Y) exposed to hypertonic media for 1 h behave as osmometers, but in hypotonic media, after initial swelling, they shrink back to normal volume and maintain it for long periods of time. The lower limit of osmolarity at which this “volume adaptation” will occur lies between 140 and 185 mosM. The “volume adaptation” is associated with a loss of cellular K⁺ probably due to a transient increase in K⁺ permeability and to loss of associated anions and osmotically obliged water. Partial dissipation of the large gradient of K⁺ between cells and medium by pre-exposure to ouabain or to K⁺-free medium results in a diminished capacity to adapt. After the shrinking phase is completed, a new steady state is established with a reduced cellular K⁺ content, normal Na⁺, normal K⁺-permeability, and a reduced activity of the Na⁺ ? K⁺ transport system. When adapted cells are returned to normal medium, an initial shrinking is followed by a re-swelling to normal size, associated with a gain in K⁺ content, presumably due to the return to normal activity of the Na⁺ ? K⁺ transport system.