Beta-Blockers Are a Class of Drugs That Target Beta-Adrenergic Receptors

Beta-blockers are a class of drugs that target beta-adrenergic receptors, blocking the action of epinephrine and norepinephrine. These drugs are used to treat heart conditions, hypertension, glaucoma, and migraine headaches and are also used off-label to alleviate stage fright in performers. Since the beta-adrenergic receptor is a GPCR, what intracellular event is prevented by the use of a beta-blocker?

A) a protein kinase cascade, initiated by the receptor's intracellular kinase domain
B) release of an activated G protein subunit bound to GTP
C) transport of the receptor-hormone complex into the cell and the nucleus, where it would regulate transcription
D) a protein phosphatase cascade, initiated by the receptor's intracellular phosphatase domain