CRH-elicited cAMP response depends on bicarbonate. (A) HT22-CRHR1 cells were stimulated with CRH in HCO3−-free or 25 mM HCO3− DMEM. (B) HT22-CRHR1 cells preincubated with vehicle (control) or anion channel blocker DIDS were stimulated with CRH. pERK1/2 and total ERK1/2 were measured and expressed as the percentage of maximum pERK1/2 under control conditions (mean ± SEM, n = 3). *, P < 0.05; **, P < 0.01 by Student’s t test. (C) Proposed model: CRH-activated CRHR1 at the plasma membrane generates cAMP and intracellular calcium increase. G protein–dependent tmACs and calcium-activated sAC contribute to cAMP generation, which engages PKA and EPAC in acute ERK1/2 activation (early phase). Rapid CRHR1 internalization leading to G protein–independent sustained ERK1/2 activation (late phase) requires cAMP generated through sAC via EPAC.
