REGULATORY VOLUME DECREASE OF CULTURED HUMAN FIBROBLASTS INVOLVES CHANGES IN INTRACELLULAR AMINO-ACID POOL

Regulatory volume decrease (RVD) has been studied in cultured human fi broblasts incubated in a complete growth medium at low osmolality (215 mosmolal). After the initial swelling induced by hypotonic treatment, cells recover their volume almost completely within about 60 min. Thi s RVD is associated with comparable losses of cell potassium and amino acids. After an initial increase, cell content of sodium is kept at v alues dose to control. Chromatographic analysis of intracellular amino -acid pool has shown that RVD-associated decrease in cell amino acids is due for the most part to changes in the intracellular concentration of L-glutamine. RVD-exerting cells undergo a rapid and marked depolar ization that is maintained after cell volume recovery. This change in membrane potential has been detected with measurements of both the tra nsmembrane distribution ratios of L-arginine and of fluorescence of po tential-sensitive dye bis-oxonol. Due to depolarization, the trans-mem brane gradient of sodium electrochemical potential is lowered. It is p roposed that cell depolarization concurs to keep the intracellular con centration of amino acids low by inhibiting sodium-coupled uptake thro ugh system A.