Figure 3.

cGMP impairs IP₃R-mediated release of Ca²⁺ from the SR and activation of TRPM4. (A) Representative confocal images of a time course of Ca²⁺ signals in a Fluo-4-AM–loaded SMC treated with vehicle, and a trace showing changes in fractional fluorescence (F/F₀) in response to U46619 (100 nM) and caffeine (10 mM) Scale bar = 10 µm. (B) Representative confocal images of a time course of Ca²⁺ signals in an SMC treated with dibutyryl-cGMP (1 µM), and a trace showing changes in fractional fluorescence (F/F₀) in response to U46619 (100 nM) and caffeine (10 mM) Scale bar = 10 µm. (C) Summary data showing the change in fractional fluorescence (ΔF/F₀) in response to U46619 in SMCs treated with vehicle or dibutyryl-cGMP (*P < .05; vehicle, n = 11 cells from five animals; dibutyryl-cGMP, n = 14 cells from five animals). (D) Summary data showing no significant difference in the change in fractional fluorescence (ΔF/F₀) in response to caffeine (10 mM) between SMCs treated with vehicle and those treated with dibutyryl-cGMP (vehicle, n = 7 cells from three animals; dibutyryl-cGMP, n = 9 cells from three animals). (E) Representative trace from a perforated patch-clamp experiment demonstrating that TICC activity is significantly increased by Bt₃IP₃-AM (10 µM) and inhibited by SNAP (30 µM). (F) Summary data showing that the increase in TICC activity in response to Bt₃IP₃ is diminished by SNAP (*P < .05; n = 9 cells from five animals). (G) Representative trace from a perforated patch-clamp experiment demonstrating that TICC activity induced by negative pressure (−20 mmHg), applied through the patch pipette, is inhibited by dibutyryl-cGMP (0.5 µM) and cannot be rescued by Bt₃IP₃-AM (10 µM). (H) Summary data showing that inhibition of TICC activity in response to dibutyryl-cGMP is not restored by Bt₃IP₃-AM (*P < .05; n = 7 cells from four animals).