ACUTE GLUCOSE OVERLOAD ABOLISHES CA2-CELLS FROM BOVINE AORTA - A POSSIBLE ROLE OF SUPEROXIDE ANION( OSCILLATION IN CULTURED ENDOTHELIAL)

Effects of acute glucose overload on [Ca2+](i) were investigated in cu ltured endothelial cells from bovine aorta. Application of 0.1 mu mol/ L ATP elicited an oscillatory increase in [Ca2+](i) (Ca2+ oscillation) in Krebs solution containing 11.5 mmol/L glucose. The frequency of Ca 2+ oscillation induced by ATP increased in a concentration-dependent m anner, ranging between 0.03 and 1 mu mol/L. When cells were preincubat ed with 23 mmol/L glucose-containing Krebs solution (high glucose solu tion) for 3 hours, 0.1 mu mol/L ATP failed to induce Ca2+ oscillation but evoked only a phasic followed by sustained increase in [Ca2+](i). Application of a higher concentration of ATP (10 mu mol/L) evoked a tr ansient increase in [Ca2+](i) both in control and high glucose-treated cells. However, the falling phase of [Ca2+](i) was prolonged in high glucose-treated cells, Thapsigargin (1 mu mol/L), an inhibitor of endo plasmic Ca2+-ATPase, induced a transient followed by a sustained incre ase in [Ca2+](i) in control cells. Preincubation with high glucose sol ution increased the rate of rise of the thapsigargin-induced increase in [Ca2+](i) and abolished the sustained increase, suggesting that glu cose overload accelerates Ca2+ leak from intracellular store sites and impairs Ca2+ release-activated Ca2+ entry. We found that all of the g lucose overload-induced changes in Ca2+ mobilization could be mimicked by xanthine with xanthine oxidase and abolished by superoxide dismuta se. These results indicate that acute glucose overload accumulates sup eroxide anion in bovine aortic endothelial cells, thereby diminishing ATP-induced Ca2+ oscillation through the impairment of Ca2+ homeostasi s.