INTEGRIN AND CYTOSKELETAL INVOLVEMENT IN SIGNALING CELL-VOLUME CHANGES TO GLUTAMINE TRANSPORT IN RAT SKELETAL-MUSCLE

1. Muscle glutamine transport is modulated in response to changes in c ell volume by a mechanism dependent on active phosphatidylinositol 3-k inase. We investigated the possibility that this mechanism requires in teractions between the extracellular matrix (ECM), integrins and the c ytoskeleton as components of a mechanochemical transduction system. 2. Using skeletal muscle cells, we studied effects of (a) inactivating i ntegrin-substratum interactions by using integrin-binding peptide GRGD TP with inactive peptide GRGESP as control, and (b) disrupting the cyt oskeleton using colchicine or cytochalasin D, on glutamine transport a fter 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 t he increase (71 %) and decrease (39 %) in glutamine uptake in response to hypo- and hyperosmotic exposure, respectively. 4. Colchicine and c ytochalasin D prevented the increase and decrease in glutamine uptake in response to changes in external osmolality. They also increased bas al glutamine uptake by 59 +/- 19 and 85 +/- 16 %, respectively, in a w ortmannin-sensitive manner. 5. These results indicate involvement of E CM-integrin-mediated cell adhesion and the cytoskeleton in mechanochem ical transduction of cell volume changes to chemical signals modulatin g glutamine transport in skeletal muscle. Phosphatidylinositol 3-kinas e may function to maintain the mechanotransducer in an active state.