Inhibition of increasing effect of vanadate on glycogen content and lipoprotein lipase activity in fat pads by 5-N,N-hexamethylene amiloride.

Abstract

Sodium orthovanadate (vanadate) increased the glycogen content in isolated rat fat pads in a dose-dependent manner up to 2 mM. Biochanin A, a specific inhibitor of tyrosine kinases, inhibited the increasing effect of vanadate or insulin on both glycogen content and lipoprotein lipase (LPL) activity in fat pads. The increasing effect of vanadate on glycogen content was not decreased by the replacement of Na+ with choline ion in the incubation medium. 5-N,N-Hexamethylene amiloride, a potent inhibitor of the Na+/H+ exchange system, showed a 50%-inhibition of the vanadate-increased LPL activity and glycogen content at 25 and 80 microM, respectively, suggesting that mechanisms of the inhibition differ in part between the vanadate actions. Furthermore, a similar inhibitory profile of the vanadate-increased glycogen content was observed with incubation in the presence of absence of Na+ in the medium. These results suggest that the activation of the Na+/H+ exchange system by vanadate is not involved in an increase in the glycogen content in fat pads.