Integrin and Cytoskeletal Involvement in Signalling Cell Volume Changes to Glutamine Transport in Rat Skeletal Muscle

1. Muscle glutamine transport is modulated in response to changes in cell volume by a mechanism dependent on active phosphatidylinositol 3-kinase. We investigated the possibility that this mechanism requires interactions between the extracellular matrix (ECM), integrins and the cytoskeleton as components of a mechanochemical transduction system. 2. Using skeletal muscle cells, we studied effects of (a) inactivating integrin-substratum interactions by using integrin-binding peptide GRGDTP with inactive peptide GRGESP as control, and (b) disrupting the cytoskeleton using colchicine or cytochalasin D, on glutamine transport after brief exposure to hypo-osmotic, isosmotic or hyperosmotic medium (170, 300 and 430 mosmol kg-1, respectively). 3. Neither GRGDTP nor GRGESP significantly affected basal glutamine uptake (0.05 mM; 338 +/- 58 pmol min-1 (mg protein)-1) but GRGDTP specifically prevented the increase (71%) and decrease (39%) in glutamine uptake in response to hypo- and hyperosmotic exposure, respectively. 4. Colchicine and cytochalasin D prevented the increase and decrease in glutamine uptake in response to changes in external osmolality. They also increased basal glutamine uptake by 59 +/- 19 and 85 +/- 16%, respectively, in a wortmannin-sensitive manner. 5. These results indicate involvement of ECM-integrin-mediated cell adhesion and the cytoskeleton in mechanochemical transduction of cell volume changes to chemical signals modulating glutamine transport in skeletal muscle. Phosphatidylinositol 3-kinase may function to maintain the mechanotransducer in an active state.