Abstract P153: Crosstalk Between Vascular Redox and Calcium Signalling in Hypertension Involves Transient Receptor Potential Melastatin 2 (TRPM2) Channel

Abstract

Mechanisms involved in redox-sensitive calcium signalling in hypertension are elusive. TRPM2 is a cation channel permeable to Ca2+ that is highly sensitive to increased levels of H2O2. TRPM2 also regulates Na+ influx, which may influence the sodium-calcium exchanger (NCX), which in reverse mode, promotes Ca2+ influx. We hypothesise that vascular oxidative stress in hypertension causes TRPM2 activation, increased influx of Ca2+ and vascular dysfunction. Vascular smooth muscle cells (VSMCs) from hypertensive and normotensive subjects and mesenteric arteries from wildtype (WT) and hypertensive LinA3 mice (human renin-expressing mice) were used. H2O2 levels were increased in hypertensive VSMCs (% of control:188.6±36.3), followed by increased activity of TRPM2 modulator PARP1 (% of control: 158.4±18.7), effect reversed by PEG-Catalase (104.1±7.0), suggesting an event regulated by H2O2. Higher calcium influx in hypertensive VSMCs (AUC NT 15710±812.3 vs HT 21440 ± 1685) was normalized by PEG-Catalase, and TRPM2 inhibitors (2-APB, Olaparib and 8-Br-cADPR) and by Na+ depletion and NCX inhibitors (Benzamil, KB-R7943 and YM 244769). Phosphorylation of the pro-contractile signaling protein, MLC20 in VSMCs from hypertensive patients (% of control 186.3±21.5) and agonist-induced vascular responses in LinA3 mice (max response: NT 0.29±6.7 vs HT 9.3±0.5) were attenuated by inhibitors of TRPM2 and NCX. These results demonstrate that in hypertension vascular oxidative stress influences TRPM2-mediated Ca2+ and Na+ homeostasis, through processes that involve NCX activation. Our findings identify novel signalling pathways linking ROS-TRPM2-Ca2+-Na+, which may play a role in hypercontractile responses in hypertension. We highlight redox-sensitive TRPM2 as a putative vascular target in hypertension.