ISOVOLUMETRIC REGULATION OF C6 RAT GLIOMA-CELLS IN HYPEROSMOTIC MEDIA

Volume regulation of C6 glioma cells was studied in response to a grad ual increase of extracellular osmolality from 300 to 440 mosmol/kgH(2) O at 37 degrees C. Maintenance of cell size depended on the rate of os molality increase (C-R); at C-R of 3 mosmol . kg(-1). min(-1), cell vo lume was kept constant, whereas it decreased progressively at C-R of 6 or 9 mosmol . kg(-1). min(-1). The ability of C6 cells to maintain th eir volume is termed isovolumetric regulation (IVR). Reducing temperat ure to 22 degrees C inhibited IVR significantly. Also, bumetanide and ouabain blocked the regulation, while 5-(N,N-dimethyl)amiloride (DMA) did not affect TVR. Extracellular acidification rate (EAR) was studied by microphysiometry. EAR gradually decreased in the presence and incr eased in the absence of IVR. Experiments with DMA show that these chan ges in EAR were related to the activity of the Na+/H+ exchanger. It wa s stimulated by cell shrinkage but not by hyperosmolality itself. Our data demonstrate that C6 glioma cells are able to prevent Volume decre ase at a low rate of elevation of external osmolality and at 37 degree s C. This process requires electrolyte uptake by the Na+-K+-2Cl(-) cot ransporter and Na+/K+ pump.