Pathways of Intracellular Signal Transduction

A: Correct! Cyclic AMP activates protein kinase A, which then stimulates the breakdown of glycogen into glucose, and also alters the pattern of gene expression via activation of the transcription factor CREB.

B: Incorrect. Although cAMP can regulate ion channels such as sodium channels in sensory neurons, it is not the primary means by which it exerts its effects.

C: Incorrect. Protein kinase C is not activated by cAMP, but rather by diacylglycerol.

D: Incorrect. cAMP phosphodiesterase is the enzyme that breaks down cAMP to AMP."