Fig. 4.

Changes in cAMP activity associated with lipid raft and nonraft plasma membrane domains after β₂AR stimulation in the presence of PKA inhibition. Representative time course of changes in magnitude of FRET response (ΔR/R₀) detected by Epac2-MyrPalm and Epac2-CAAX biosensors after inhibition of PKA activity with H89 (1 µM) and subsequent activation of β₂ARs with 3 nM isoproterenol (Iso) in (A) untreated human ASM cells (control) and (B) human ASM cells overexpressing (OE) AC6. Results are normalized to the magnitude of the maximal response produced by forskolin (FSK, 10 µM) and IBMX (100 µM) in the same cell. (C) Size of average FRET responses in control cells (black bars) and AC6 OE cells (red bars). In the presence of H89, there were no significant (P > 0.05, Student’s t test) differences in the magnitude of the responses to Iso detected by Epac2-MyrPalm in control (n/N = 6/4) and AC6 OE (n/N = 6/4) cells or those detected by Epac2-CAAX in control (n/N = 9/7) and AC6 OE (n/N = 6/4) cells.