Fig. 2. HT-29 cells display low PKA-dependent phosphorylation in response to high cAMP levels.
A HeLa (averaged traces ± SD of six cells from one experiment) or B HT-29 cells (averaged traces ± SD of seven cells from one experiment) expressing the cAMP-sensitive FRET-based sensor H187 were challenged with increasing doses of forskolin (FSK) followed by FSK (20 µM) together with IBMX 500 µM (FSK/IBMX) to saturate the sensor. C HeLa cells expressing the PKA-dependent phosphorylation sensor AKAR4 marginally responded to FSK alone; however, addition of IBMX 500 µM produced a near-saturation response. Saturation was achieved by FSK/IBMX (averaged traces ± SD of 20 cells from four independent experiments). D In HT-29 cells AKAR4 gave extremely low responses independent of the treatment (averaged traces ± SD of 37 cells from 15 independent experiments).