What is the function of phosphodiesterases?

What is the function of phosphodiesterases?

• A. Break down cAMP and cGMP
• B. Synthesize cAMP and cGMP
• C. Break down ATP
• D. Synthesize second messengers

Answer: (A)

PDEs regulate intracellular signaling by terminating signals carried by cyclic nucleotides. They do this by hydrolyzing the phosphodiester bond in cyclic AMP and cyclic GMP, converting them to the inactive forms AMP and GMP. This lowers the levels of cAMP and cGMP inside the cell, dampening downstream pathways such as PKA and PKG signaling that would otherwise propagate the signal. In practice, this means PDE activity shortens the duration of the signal, while inhibitors of PDEs raise these second-messenger levels to enhance signaling—milrinone (a PDE3 inhibitor) increases cAMP to boost cardiac contractility, and sildenafil (a PDE5 inhibitor) raises cGMP to promote vasodilation. The other options describe synthesis of these messengers or breakdown of ATP, which are not functions of phosphodiesterases.

PDEs regulate intracellular signaling by terminating signals carried by cyclic nucleotides. They do this by hydrolyzing the phosphodiester bond in cyclic AMP and cyclic GMP, converting them to the inactive forms AMP and GMP. This lowers the levels of cAMP and cGMP inside the cell, dampening downstream pathways such as PKA and PKG signaling that would otherwise propagate the signal. In practice, this means PDE activity shortens the duration of the signal, while inhibitors of PDEs raise these second-messenger levels to enhance signaling—milrinone (a PDE3 inhibitor) increases cAMP to boost cardiac contractility, and sildenafil (a PDE5 inhibitor) raises cGMP to promote vasodilation. The other options describe synthesis of these messengers or breakdown of ATP, which are not functions of phosphodiesterases.