A9595 Crosstalk Between Vascular Redox and Calcium Signalling in Hypertension Involves Transient Receptor Potential Melastatin 2 Channel Activation

Abstract

Objectives: ROS regulates Ca2+ homeostasis by mechanisms still not fully understood. TRPM2, a redox-sensitive channel permeable to Ca2+ and Na+, is activated by H2O2 via oxidation or ADPR production. We tested the hypothesis that TRPM2 is a molecular target of ROS leading to regulation of Ca2+ levels and vascular function in hypertension. Methods: VSMCs from normotensive and hypertensive subject were used. Ca2+ and Na+ influx was assessed by fluorescence microscopy. Results: O2- (1.65 fold) and H2O2 (1.88 fold) generation were enhanced in VSMCs from hypertensive subjects (p < 0.05). Ca2+ (AUC: 1.36 fold) and Na+ influx (AUC: 1.2 fold) were also increased in cells from hypertensive subjects (p < 0.05), an effect blocked by PEG-catalase and, 2-APB, 8-br or olaparib (TRPM2 inhibitors). Additionally, in the absence of Na+, [Ca2+]i was reduced to levels detected in cells from normotensive subjects. TRPM2-induced Na+ influx may influence the sodium-calcium exchanger (NCX), which in reverse mode, promotes Ca2+ influx. Benzamil, KB-R7943 and YM244769 (NCX inhibitors) also ameliorated the increased Ca2+ influx observed in hypertension. MLC20 activation, a marker of cell contraction, was increased in VSMCs from hypertensive subjects (1.72 fold), an effect reversed by TRPM2 and NCX inhibitors (p < 0.05). Arteries from hypertensive mice exhibit increased TRPM2 (1.5 fold) and NCX (1.9 fold) mRNA expression and increased U46619-induced vasoconstriction (Emax: 7.6 ± 0.2 vs 10.21 ± 0.3), effect reversed by TRPM2 and NCX inhibitors (p < 0.05). Conclusion: In conclusion, activation of redox-dependent TRPM2 channel contributes to increased calcium and sodium influx, partially through NCX activation. The results highlight a novel pathway linking ROS to Ca2+ and Na+ signalling through TRPM2/NCX, leading to vascular dysfunction in hypertension.