RESUMO
AIMS/HYPOTHESIS: Na(+)/K(+)-ATPase inhibition by ouabain suppresses ATP production by generating reactive oxygen species (ROS) and impairs glucose-induced insulin secretion from pancreatic islets. To clarify the signal-transducing function of Na(+)/K(+)-ATPase in decreasing ATP production by the generation of ROS in pancreatic islets, the involvement of Src was examined. In addition, the significance of Src activation in diabetic islets was examined. METHODS: Isolated islets from Wistar rats and diabetic Goto-Kakizaki (GK) rats (a model for diabetes) were used. ROS was measured by 5-(and 6)-chloromethyl-2',7'-dichlorofluorescein fluorescence using dispersed islet cells. After lysates were immunoprecipitated by anti-Src antibody, immunoblotting was performed. RESULTS: Ouabain caused a rapid Tyr(418) phosphorylation, indicating activation of Src in the presence of high glucose. The specific Src inhibitor 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP2) restored the ouabain-induced decrease in ATP content and the increase in ROS production. Both PP2 and ROS scavenger restored the impaired insulin release and impaired ATP elevation in GK islets, but had no such effect in control islets. PP2 reduced the high glucose-induced increase in ROS generation in GK islet cells but had no effect on that in control islet cells. Moreover, ouabain had no effect on ATP content and ROS production in the presence of high glucose in GK islets. CONCLUSIONS/INTERPRETATION: These results indicate that Src plays a role in the signal-transducing function of Na(+)/K(+)-ATPase, in which ROS generation decreases ATP production in control islets. Moreover, ROS generated by Src activation plays an important role in impaired glucose-induced insulin secretion in GK islets, in which Src is endogenously activated independently of ouabain.