Angiotensin-2-Mediated Ca2+ Signaling in the Retinal Pigment Epithelium: Role of Angiotensin-Receptor- Associated-Protein and TRPV2 Channel

Angiotensin II (AngII) receptor (ATR) is involved in pathologic local events such as neovascularisation and inflammation including in the brain and retina. The retinal pigment epithelium (RPE) expresses ATR in its AT1R form, angiotensin-receptor-associated protein (Atrap), and transient-receptor-potential channel-V2 (TRPV2). AT1R and Atrap co-localize to the basolateral membrane of the RPE, as shown by immunostaining. Stimulation of porcine RPE (pRPE) cells by AngII results in biphasic increases in intracellular free Ca²⁺inhibited by losartan. Xestospongin C (xest C) and U-73122, blockers of IP3R and PLC respectively, reduced AngII-evoked Ca²⁺response. RPE cells from Atrap^−/− mice showed smaller AngII-evoked Ca²⁺peak (by 22%) and loss of sustained Ca²⁺elevation compared to wild-type. The TRPV channel activator cannabidiol (CBD) at 15 µM stimulates intracellular Ca²⁺-rise suggesting that porcine RPE cells express TRPV2 channels. Further evidence supporting the functional expression of TRPV2 channels comes from experiments in which 100 µM {"type":"entrez-protein","attrs":{"text":"SKF96365","term_id":"1156357400","term_text":"SKF96365"}}SKF96365 (a TRPV channel inhibitor) reduced the cannabidiol-induced Ca²⁺-rise. Application of {"type":"entrez-protein","attrs":{"text":"SKF96365","term_id":"1156357400","term_text":"SKF96365"}}SKF96365 or reduction of TRPV2 expression by siRNA reduced the sustained phase of AngII-mediated Ca²⁺transients by 53%. Thus systemic AngII, an effector of the local renin-angiotensin system stimulates biphasic Ca²⁺transients in the RPE by releasing Ca²⁺from cytosolic IP3-dependent stores and activating ATR/Atrap and TRPV2 channels to generate a sustained Ca²⁺elevation.