ELECTROLYTE TRANSPORT MECHANISMS INVOLVED IN REGULATORY VOLUME INCREASE IN C6 GLIOMA-CELLS

Volume regulation of C6 glioma cells was studied with an automatic sys tem for monitoring cell thickness, while increasing bath osmolality fr om 300 to 440 mosmol/kgH(2)O. At 37 degrees C, tissues incubated in so lutions containing active substances (inositol, D-biotin, hydrocortiso ne, prostaglandin El, insulin, transferrin, sodium selenite, and 3,5,3 '-triiodothyronine) responded to hyperosmotic challenge with a typical regulatory volume increase (RVI). Lowering temperature or removing th e active substances inhibited osmoregulation. Bumetanide, amiloride, 4 ,4' -diisothiocyanostilbene-2,2'-disulfonic acid, or ouabain significa ntly reduced RVI. Ion substitutions of Na+, Cl-, NaCl, or HCO3- also i mportantly affected the process. Extracellular acidification rate (EAR ) was studied by microphysiometry. Hyperosmotic shock induced an incre ase in EAR with a time course that matched volume recovery. This incre ase in EAR was prevented by amiloride. The data show that under hypero smotic conditions C6 cells are able to regulate their volume. Ion subs titutions and application of blockers demonstrate that Na+/H+ and Cl-/ HCO3- exchangers and Na+-K+-2Cl(-) cotransporter are involved in RVI. The rise in EAR is due to the enhanced activity of Na+/H+ antiporter, which seems to be volume dependent but not osmotic dependent.