Question

ring a blood pressure drop, sympathetic stimulation normally causes arteriole
ooth muscle to contract and restore vascular resistance. a patient is given a drug
at prevents certain contractile proteins in vascular smooth muscle from changing
shape after atp is used.

despite strong sympathetic signals, the patient’s arterioles remain widely dilated and
blood pressure stays low.

which explanation best accounts for this failure of the arterioles to constrict?

the drug prevents phosphorylation - dependent conformational changes that
\energize\ the contractile proteins, so smooth muscle cannot shift into its active
form and cannot constrict the vessel.

arteriole smooth muscle relaxes because atp becomes unable to bind actin
during sympathetic stimulation, even though the contractile proteins still change
shape normally.

the drug prevents sodium ions from diffusing through the membrane, and
arteriole constriction depends entirely on sodium diffusion rather than protein
shape changes.

Explanation:

1. Analyze Option 1: The problem states the drug prevents contractile proteins from changing shape after ATP use. Phosphorylation - dependent conformational changes "energize" contractile proteins. If the drug stops these changes, smooth muscle can't activate to constrict, matching the scenario of dilated arterioles and low BP.
2. Analyze Option 2: ATP binding to myosin (not actin) is key in muscle contraction. Also, the drug is said to prevent protein shape change after ATP use, so contractile proteins shouldn't be changing shape normally here, making this option inconsistent.
3. Analyze Option 3: Arteriole constriction relies on smooth muscle contraction (protein shape changes), not just sodium diffusion. So this option's mechanism is incorrect.

Answer:

The drug prevents phosphorylation - dependent conformational changes that "energize" the contractile proteins, so smooth muscle cannot shift into its active form and cannot constrict the vessel.