MECHANISMS OF REGULATORY VOLUME DECREASE IN UC-11MG HUMAN ASTROCYTOMA-CELLS

Swelling of astrocytes commonly occurs after cerebral ischemia and oth er brain injuries. Because these cells constitute 20-25% of human brai n volume, their swelling is a major factor in the morbidity and mortal ity associated with cerebral edema. Many cells, including astrocytes, resist or reverse the tendency to swell by activating transport pathwa ys that lead to a regulatory volume decrease. Here we report the resul ts of studies designed to elucidate the mechanisms of the regulatory v olume decrease that occurs after astrocytes are swollen by exposure to hypotonic medium. Using UC-11MG cells, a well-characterized, human, a strocytoma-derived line, we observed an increase in membrane permeabil ity to both K+ and Cl- during regulatory volume decrease, consistent w ith a net loss of these ions. Neither the increase in K+ exit nor the regulatory volume decrease was affected by bumetanide, an inhibitor of anion-cation cotransport. On the other hand, the increased K+ efflux, as well as the regulatory volume decrease, was blocked by Gd3+, sugge sting a putative role of stretch-activated cationic channels in the pr ocess of volume regulation. Although increases in intracellular free C a2+ were also observed during hypotonic treatment, they occurred well after the onset of the regulatory volume decrease. Furthermore, the re gulatory volume decrease was not affected by blocking the intracellula r free Ca2+ increase with dimethyl ,2-bis(2-aminophenoxy)ethane-N,N,N' ,N'-tetraacetic acid or by removal of extracellular Ca2+. These result s indicate that the regulatory volume decrease in UC-11MG cells may in volve stretch-activated channels that operate independently of changes in intracellular free Ca2+.