To activate a G protein-coupled receptor permanently with cell surface photodynamic action in the gastrointestinal tract

Figure 2 Permanent photodynamic activation of cholecystokinin 1 receptor. A: Photodynamic action with sulphonated aluminum phthalocyanine (SALPC) (1 μmol/L; light λ > 580 nm, 53000 Lux/ 72.4 mW/cm²) triggered persistent calcium oscillations in perifused rat pancreatic acini loaded with Fura-2 AM, which were completely blocked by cholecystokinin 1 receptor (CCK1R) antagonist FK480 (10 nM); after blockade by FK480, the muscarinic agonist bethanechol (5 μmol/L) could still elicit a robust calcium response. Modified from An et al[28]. Note that the photosensitizer SALPC was exposed to perifused rat pancreatic acini only briefly (10 minutes) then washed out, only residue photosensitizer remaining on the acinar cell plasma membrane was then irradiated by red light. Reproduced from An et al[28]; B: The human CCK1R (green) was expressed in HEK293 cells, as detected by immunocytochemsitry. Scale bar: 10 μm. Modified from Jiang et al[13]; C: The positively expressing human CCK1R-HEK293 cells were loaded with fluorescent calcium indicator Fura-2 AM, perifused, CCK 20 pM, SALPC 2 μmol/L and light (λ > 580 nm, 20500 Lux/ 36.7 mW/cm²) were applied as indicated. Note the reversible calcium oscillations with CCK 20 pM stimulation, but persistent calcium oscillations after photodynamic action with SALPC. Modified from Jiang et al[13]. Note that the photosensitizer SALPC was exposed to perifused human CCK1R-HEK293 cells only for 10 minutes before wash out. Only residual photosensitizer SALPC on the plasma membrane was irradiated by red light (> 580 nm). Note that the peripheral sulphate groups (4) of SALPC structure ensure aqueous solubility and little ability to enter the cell interiors, enabling plasma membrane specificity. Reproduced from Jiang et al[13]. SALPC: Sulphonated aluminum phthalocyanine; hCCK1R: Human cholecystokinin 1 receptor. Citation for Figure 2A: An YP, Xiao R, Cui H, Cui ZJ. Selective activation by photodynamic action of cholecystokinin receptor in the freshly isolated rat pancreatic acini. Br J Pharmacol 2003; 139: 872-880. Copyright© Nature Publishing Group 2003. Published by John Wiley and Sons; Citation for Figure 2B and C: Jiang HN, Li Y, Jiang WY, Cui ZJ. Cholecystokinin 1 Receptor - A Unique G Protein-Coupled Receptor Activated by Singlet Oxygen (GPCR-ABSO). Front Physiol 2018; 9: 497. Copyright© The Authors 2018. Published by Frontiers Media S.A. The authors have obtained the permission for figure using (Supplementary material).