Acute glucose overload abolishes Ca²⁺ oscillation in cultured endothelial cells from bovine aorta: A possible role of superoxide anion

Effects of acute glucose overload on [Ca²⁺](i) were investigated in cultured endothelial cells from bovine aorta. Application of 0.1 μmol/L ATP elicited an oscillatory increase in [Ca²⁺](i) (Ca²⁺ oscillation) in Krebs solution containing 11.5 mmol/L glucose. The frequency of Ca²⁺ oscillation induced by ATP increased in a concentration-dependent manner, ranging between 0.03 and 1 μmol/L. When cells were preincubated with 23 mmol/L glucose- containing Krebs solution (high glucose solution) for 3 hours, 0.1 μmol/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 μmol/L) evoked a transient 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 μmol/L), an inhibitor of endoplasmic Ca²⁺-ATPase, induced a transient followed by a sustained increase in [Ca²⁺](i) in control cells. Preincubation with high glucose solution increased the rate of rise of the thapsigargin-induced increase in [Ca²⁺](i) and abolished the sustained increase, suggesting that glucose overload accelerates Ca²⁺ leak from intracellular store sites and impairs Ca²⁺ release-activated Ca²⁺ entry. We found that all of the glucose overload-induced changes in Ca²⁺ mobilization could be mimicked by xanthine with xanthine oxidase and abolished by superoxide dismutase. These results indicate that acute glucose overload accumulates superoxide anion in bovine aortic endothelial cells, thereby diminishing ATP-induced Ca²⁺ oscillation through the impairment of Ca²⁺ homeostasis.