Effect of osmolality and anion channel inhibitors on myo-inositol efflux in cultured astrocytes

Recent studies have shown that swelling-activated myo-inositol efflux from rat C6 glioma cells is mediated by a single transport mechanism and most li kely by a volume-sensitive anion channel. In those studies, cells were accl imated in hypertonic medium and then swollen by returning the cells to isot onic medium. In the present study, myo-inositol efflux was determined in pr imary cultures of astrocytes by first incubating the cells in isotonic radi olabelled medium for 2 hr and then placing the cells in either unlabelled i sotonic, hypertonic, or hypotonic medium and measuring release with time. C omputer analyses of efflux data indicated a two-component system of myo-ino sitol efflux. The rate constants for the initial fast component for isotoni c and hypotonic cells were 0.0398 +/- 0.005 and 0.0631 +/- 0.0288 min(-1), respectively. The efflux rates of the slow component, while quite small, we re severalfold greater with increasing hypotonic media as compared to the c ells in isotonic medium. Several anion membrane transport inhibitors were t ested to explore the swelling activated efflux mechanism of myo-inositol, F urosemide (0.5 mM), 1,9 dideoxyforskolin (0.1 mM), NPPB (0.1 mM), niflumic acid (0.5 mM), and SITS (0.5 mM) blocked the fast component of myo-inositol efflux by 17, 49, 55, 75, and 93%, respectively. Our results suggest that the fast component of myo-inositol efflux in primary cultures of astrocytes is mediated by anion transporters or channels and that myo-inositol flux c ontributes to cell volume regulation in cultures of primary astrocytes, (C) 1999 Wiley-Liss, Inc.