In what way does GPCR signaling terminate?

GPCR signaling termination is primarily achieved through the degradation of cAMP. When a G protein-coupled receptor (GPCR) is activated, it typically stimulates the production of cyclic adenosine monophosphate (cAMP) by activating adenylate cyclase. The intracellular concentration of cAMP then leads to the activation of various downstream signaling pathways. To terminate this signal, the cellular concentration of cAMP must be reduced.

This degradation occurs mainly via the action of phosphodiesterases (PDEs), which hydrolyze cAMP to AMP. This hydrolysis reduces the levels of cAMP in the cell, consequently leading to the cessation of the physiological responses initiated by the GPCR activation. This process is critical for ensuring that the signaling is not prolonged unnecessarily, allowing the cell to return to its baseline state and respond to new stimuli effectively.

While internalization of receptors and receptor phosphorylation are processes that also play roles in the regulation of GPCR activity, they do not primarily focus on the degradation of the signaling molecule itself, which is central to the termination of the signal. Synthesis of more cAMP would in fact amplify the signal rather than terminate it. Thus, the correct answer is grounded in the essential biochemical step of reducing cAMP