Caffeine prolongs and intensifies the effects of epinephrine. Which of the following potential mechanisms of action of caffeine is consistent with this effect? a. inhibits cAMP phosphodiesterase, the enzyme that converts cAMP to AMP.
b. a competitive antagonist of cAMP binding to PKA.
c. stimulates phospholipase Cb.
d. inhibits sarcoplasmic/endoplasmic reticulum Ca 2 + - ATPase.
e. activates PKC.

a. inhibits cAMP phosphodiesterase, the enzyme that converts cAMP to AMP.

Explanation:

The phosphodiesterases are a group of enzymes that are capable of breaking phosphodiester bonds such as those between nucleotides in nucleic acids. The Cyclic adenosine monophosphate (cAMP) is a second messenger involved in intracellular signaling pathways. This molecule (cAMP) is hydrolyzed by the cAMP-dependent phosphodiesterase, which catalyzes the enzymatic breakdown of phosphodiester bonds (i.e., hydrolyzing cAMP to 5-AMP). The cAMP levels are modulated by the balance between its generation and the degradation via cyclic nucleotide phosphodiesterase.