By acting as a pathway for depolarisation and Ca2+-entry mechanoTRP channels are thought to play a key role in the pressure-induced vasoconstriction or “myogenic response” in vascular smooth muscle. Here we present evidence that TRPV2 forms a mechanoTRP channel in rat retinal arteriolar smooth muscle cells (SMCs) which is crucial in the generation of myogenic signalling in this tissue. Using RT-PCR and immunohistochemistry we have previous reported that TRPC1, M7, V1, V2 and P1 are expressed in the cytosol and membrane of SMCs surrounding rat retinal arterioles1; while TRPV4 expression was more prominent in the SMC nuclei. Additionally stretch-sensitive Ca2+ influxes were reversed by the TRPV2 inhibitor tranilast and the non-selective TRPP1/V2 antagonist amiloride, while inhibitors of TRPC1, M7, V1 and V4 had no effect1. In the present study we provide more definitive evidence that TRPV2 mediates stretch-activated cation currents and underpins myogenic activity in these microvessels. Sprague Dawley rats (300-500g) were sacrificed according to Schedule 1 methods; retinas extracted and arterioles isolated by trituration. Cell-attached patch-clamp and pressure myography recordings were carried out; data was tested for normality using the D’Agostino-Pearson normality test and analysed using appropriate statistical tests as indicated. Direct membrane stretch during cell-attached recordings (45mmHg negative pressure) triggered cation currents (0.38±0.10pC/s to 2.10±4.30pC/s; n=14, P<0.001, paired t-test) which were absent when either an externally targeting TRPV2 antibody (Ext TRPV2 ab; 1:100; 0.43±0.32pC/s to 0.45±0.30pC/s; n=6, P>0.05) or tranilast (100 µM) were included in the patch pipette (0.42±0.24pC/s to 0.53±0.23pC/s; n=10, P>0.05) while channel activation was still apparent in the presence of an antibody targeted towards an internal epitope of TRPV2 (Int TRPV2 Ab; 0.19±0.18pC/s to 3.90±0.42pC/s; n=7, P<0.001). Pre-incubation of vessels fragments with Ext TRPV2 Ab (1:100, 2hrs room temp.) reduced the development of myogenic tone upon pressurisation (32.6±2.1μm diameter at 0mins after inflation with 40mmHg compared to 32.0±2.1μm after 15mins inflation) and eliminated the subsequent dilatory action of tranilast (32.0±2.1μm; P>0.05, one-way ANOVA; n=11). Arterioles pre-incubated with Int TRPV2 Ab (1:100, 2hrs) developed tone (33.7±2.0μm at 0mins after inflation compared to 31.3±2.1μm after 15mins inflation; P<0.01) and dilated with application of tranilast (32.6±2.1μm; P<0.05, one-way ANOVA with post-hoc Dunnett’s multiple comparison tests; n=11). Our results confirm that TRPV2 channels are critical for the generation of myogenic tone in retinal arterioles and provide an important basis for future studies investigating why myogenic signalling and blood flow autoregulation are disrupted in ocular disease states such as diabetic retinopathy and glaucoma.
|Number of pages||1|
|Publication status||Published - 2016|