Evidence of a role for TRPV2 channels in retinal arteriolar myogenic signalling. Oral presentation

MechanoTRP channels may play a role in the pressureinduced vasoconstriction or ‘myogenic response’ by acting as a pathway for depolarisation and Ca2+ -entry in vascular smooth muscle. Here we present evidence that TRPV2 forms a mechanoTRP channel in retinal arteriolar smooth muscle cells (SMCs) which contributes to the generation of myogenic signalling in this tissue. Using RT-PCR and immunohistochemistry (IHC) a number of known mechanoTRP channels were identified in rat retinal arteriolar SMCs. Stretch sensitive responses in isolated arterioles were tested (fura-2 microfluorimetry and whole-cell patch-clamp) by reducing external osmolarity and by application of negative pressure (cell-attached patch-clamp). Myogenic tone was investigated in isolated pressurised arteriolar segments. mRNA transcripts for TRPC1, M7, V1, V2, V4 and P1 channels were detected. In contrast to larger resistance arteries, retinal arterioles do not appear to express TRPC6 or M4 channels. IHC revealed cytosolic and membrane expression of TRPC1, M7, V1, V2 and P1 in SMCs surrounding arterioles; TRPV4 expression was more prominent in the SMC nucleus than cytosol. Hypo-osmotic stretch increased [Ca2+ ]i (dependent on external Ca2+ ) which was reversed by the TRPV2 inhibitor tranilast (100 lM; n = 5) and the nonselective TRPP1/V2 antagonist amiloride (100 lM; n = 8). Inhibitors of TRPC1, M7, V1 and V4 had no effect. Hypoosmotic stretch activated currents were not consistent with activation of TRPP1 channels. Pressure-induced stretch resulted in an increase in channel activity which was absent in the presence of tranilast. Application of tranilast to pressurised retinal arterioles resulted in significant dilation (n = 9; p < 0.001, paired t-test). Our results suggest that rat retinal arteriolar SMCs express a range of mechanoTRP channels however only TRPV2 channels were found to function as mechanosensors under these conditions. Thus TRPV2 channels represent molecular candidates underpinning the myogenic response in this vascular bed.