Fig. 3: OMP sequesters a cytosolic cAMP surge.

a Scheme of the photo-uncaging of cAMP under whole-cell patch-clamp recording and the vectors used for the experiment in (d–g). Transfected HEK293T cells coexpressed GFP and DsRed with OMP and CNGA2, respectively, under the control of IRES. b Confirmation of fluorescent protein expression in transfected cells. Experiments were repeated three times with similar results. c CNGA2 channel activities in the cell-attached configuration. The red dashed line indicates the closed state. The blue dashed lines indicate the open state. d Representative UV-induced CNG currents from one cell in the absence (Ctrl) or presence of OMP, overlaid for each condition. e Normalised CNG currents (% to peak) induced by the photo-uncaging of cAMP; n = 13 and 11 cells for Ctrl and OMP( + ) cells, respectively. Statistics: one-sided unpaired T test; activation time constant, P = 0.38; decay %, P = 0.0001. f Representative UV-induced CNG currents from one cell in the presence of PDEi: overlaid for Ctrl and OMP( + ). g Normalised CNG currents (% to peak) induced by the photo-uncaging of cAMP in the presence of PDEi. Mean ± s.d.; n = 4 and 4 cells for Ctrl and OMP( + ) cells, respectively. One-sided unpaired T test; activation time constant, P = 0.78; decay %, P = 0.0002; n = 4 and 4 cells for recordings with and without OMP, respectively. h Single-compartment model without OMP. i Two-compartment model with OMP. k1–k3, the diffusion constant (k1), cAMP-eliminating activity of PDE (k2) and cAMP capture of OMP (k3). Assuming that k3 was much larger than k2, cAMP dissociation from OMP was ignored within this duration. j Simulated cAMP in the membrane compartment (C1). a.u. arbitrary unit of time. Time and [cAMP] are given in arbitrary units in the figures. k, l Schematics of the CNG channel activation time course; (k) prolonged Na⁺/Ca²⁺ influx without OMP and (l) small Na⁺/Ca²⁺ influx through rapidly deactivated CNG channels via cAMP buffering with OMP. Mean ± s.d.