Abstract

The effect of osmotic stress on sugar transport was investigated in Clone 9 epithelial cells, which express the glucose uniporter GLUT1, and in 3T3-L1 adipocytes, which express both GLUT1 and GLUT4. An acute hyperosmotic shock increased the uptake of sugars in both cell types. In Clone 9 cells, this was followed by a regulatory volume increase (RVI) response. Stimulation of transport was rapid and reversible, with half-lives (t1/2) for stimulation of 2-deoxy-D-glucose uptake of 5.6±0.9 (n=6) and 22.7±1.5 (n=4) min for Clone 9 cells and adipocytes respectively. The effect was dose dependent, reaching a maximum at 1.1 osM of 2.9±0.1-fold (n=3) for Clone 9 cells and 8.2±0.8-fold (n=3) for adipocytes. In the latter, this stimulation correlated with translocation of the glucose transporter isoform GLUT4 to the cell surface and was not significantly different from that elicited by 160 nM insulin (7.6±1.2-fold, n=3). The effect of osmotic shock was not, however, influenced by inhibitors of either phosphoinositide 3-kinase (PI 3-kinase) (wortmannin, 250 nM) or of p38 mitogen-activated protein kinase (p38 MAP kinase) (SB203580, 20 ?M), which reportedly prevent GLUT4 translocation and/or activation by insulin respectively. These inhibitors also had no effect on the stimulation of transport by osmotic shock in Clone 9 cells. However, in contrast to adipocytes, the effect of osmotic shock on glucose transport in Clone 9 cells reflected primarily a change in the intrinsic activity of cell surface transporters and there was only a minor change in their subcellular distribution as assessed by cell immunostaining or no change as assessed by surface biotinylation. These results indicate that the response of cells to osmotic shock can involve changes both in transporter activity and location. The signal transduction pathways involved include neither PI 3-kinase nor the classical, osmotically-activated component, p38 MAP kinase.