Protein S‐glutathionylation enhances Ca2+‐induced Ca2+ release via the IP3 receptor in cultured aortic endothelial cells

Abstract

Key points In non‐excitable cells, oxidative stress increases inositol 1,4,5‐trisphosphate (IP3) receptor (IP3R) activity, which can cause Ca2+ oscillations under basal conditions and enhance agonist‐stimulated changes in cytosolic free Ca2+ concentration. Protein S‐glutathionylation, the reversible modification of cysteine thiols by glutathione, is elevated in response to oxidative stress, but the consequence of glutathionylation for IP3R function is not known. In this study we provide evidence that Ca2+‐induced Ca2+‐release (CICR) via the IP3R is enhanced by oxidant‐induced glutathionylation in cultured aortic endothelial cells. Our results suggest glutathionylation may represent a fundamental mechanism for regulating IP3R activity during physiological redox signalling and during pathological oxidative stress. Abstract  In non‐excitable cells, thiol‐oxidizing agents have been shown to evoke oscillations in cytosolic free Ca2+ concentration ([Ca2+]i) by increasing the sensitivity of the inositol 1,4,5‐trisphosphate (IP3) receptor (IP3R) to IP3. Although thiol modification of the IP3R is implicated in this response, the molecular nature of the modification(s) responsible for changes in channel activity is still not well understood. Diamide is a chemical oxidant that selectively converts reduced glutathione (GSH) to its disulfide (GSSG) and promotes the formation of protein–glutathione (P‐SSG) mixed disulfide, i.e. glutathionylation. In the present study, we examined the effect of diamide, and the model oxidant hydrogen peroxide (H2O2), on oscillations in [Ca2+]i in fura‐2‐loaded bovine (BAECs) and human (HAECs) aortic endo‐thelial cells using time‐lapse fluorescence video microscopy. In the absence of extracellular Ca2+, acute treatment with either diamide or H2O2 increased the number of BAECs exhibiting asynchronous Ca2+ oscillations, whereas HAECs were unexpectedly resistant. Diamide pretreatment increased the sensitivity of HAECs to histamine‐stimulated Ca2+ oscillations and BAECs to bradykinin‐stimulated Ca2+ oscillations. Moreover, in both HAECs and BAECs, diamide dramatically increased both the rate and magnitude of the thapsigargin‐induced Ca2+ transient suggesting that Ca2+‐induced Ca2+ release (CICR) via the IP3R is enhanced by glutathionylation. Similar to diamide, H2O2 increased the sensitivity of HAECs to both histamine and thapsigargin. Lastly, biochemical studies showed that glutathionylation of native IP3R1 is increased in cells challenged with H2O2. Collectively our results reveal that thiol‐oxidizing agents primarily increase the sensitivity of the IP3R to Ca2+, i.e. enhanced CICR, and suggest that glutathionylation may represent a fundamental mechanism for regulating IP3R activity during physiological redox signalling and during pathologicalical oxidative stress.