INTERACTIONS BETWEEN EFFECTS OF W-7, INSULIN, AND HYPOXIA ON GLUCOSE-TRANSPORT IN SKELETAL-MUSCLE

The calmodulin antagonist N-(6-aminohexyl)-5-chloro-1-naphthalenesulfo namide (W-7) stimulates glucose transport in skeletal muscle, apparent ly by raising cytosolic Ca2+ (P. Palade. J. Biol. Chem. 262: 6142-6148 , 1987; J. H. Youn, E. A. Gulve, and J. O. Holloszy. Am. J. Physiol. 2 60 (Cell Physiol. 29): C555-C561, 1991). This study was performed to d escribe the Interactions between the effects of W-7 and those of hypox ia and of insulin on glucose transport. The effect on 3-O-methylglucos e (3-MG) transport of 50 mu M W-7 was additive to the effect of a maxi mal insulin stimulus (2,000 mu U/ml but not to the effect of maximal ( 60 min) hypoxic stimulus, suggesting that W-7 stimulates glucose trans port via the same pathway as hypoxia, independent of the pathway activ ated by insulin. The effect of 50 mu M W-7 was additive to that of a s ubmaximal (20 min) hypoxia stimulus, indicating that W-7 does not inte rfere with the stimulation of glucose transport by hypoxia. In contras t, 50 mu M W-7 had an inhibitory effect on stimulation of 3-MG transpo rt by submaximally effective insulin levels, causing a fivefold increa se in the concentration of insulin needed to produce a half-maximal st imulation of 3-MG transport, from similar to 70 to similar to 350 mu U /ml (P < 0.05). Thus these data demonstrate that W-7 selectively inhib its insulin stimulation of glucose transport. W-7 also inhibited the s timulation of glucose transport by vanadate, an insulin mimetic agent that stimulates glucose transport at a site distal to the insulin bind ing step, suggesting that the site of action of W-7 is at a step beyon d the insulin receptor. In conclusion, these findings provide evidence that W-7 stimulates glucose transport by the same pathway as hypoxia. In addition, this calmodulin antagonist has a specific inhibitory eff ect on insulin action on glucose transport without affecting the effec t of hypoxia.