Dynamic osmotic behavior of chick blood lymphocytes

The dynamic response of chick blood lymphocytes to hypotonic shock is investigated using electrical sizing techniques, and an attempt is made to characterize the mechanisms involved. The cells first swell rapidly, as expected, but then gradually return to their initial volume. Maximum volume is attained in 2 minutes and the return is complete within about 15 minutes at room temperature. This cycle is studied under different osmotic strengths, temperatures, and cation compositions; behavior following successive hypotonic and hypertonic shocks is also described. Metabolic inhibitors are shown to have no effect, even at relatively high concentrations, while ouabain (10 −3 M) affects only the much slower second‐order return process that sets in when the main one is blocked by appropriate external cation concentration. It is proposed that a large increase in membrane permeability to K + occurs as the cell swells beyond its iso‐osmotic volume, but none to Na + . The experimental results are then explained by ascribing the swelling to water entering the cell until the osmotic pressure inside equals that outside, and the return phase to the electrochemical potential gradient for K+ forcing it out of the swollen cell together with the associated anion and water in proportions that preserve osmotic equilibrium. This latter is a non‐active process independent of Na + whose direction can be reversed by using K + as the cation in the external medium. The existence in the literature of several related observations is pointed out and some of the implications of our findings are discussed briefly in terms of a corrugated membrane structure.