Question

Endothelin acts through which receptors?

• A. cAMP
• B. cGMP
• C. Na+ receptors
• D. Calcium receptos

Answer 1

The Correct Option is A

Step 1: Begin with the messenger. Endothelin-1 from the endothelium is one of the strongest vasoconstrictor peptides and works via GPCRs of the ETA and ETB families.
Step 2: This is a defective recall item. The answer key letter provided is A, yet the accompanying note states cGMP, which is choice b, so the source contradicts itself. As directed, the letter A (choice a, cAMP) is recorded as the keyed response.
Step 3: The accurate signalling story is worth knowing: $ET_A$ and $ET_B$ couple to $G_q$, activate phospholipase C, and elevate intracellular $Ca^{2+}$ via $IP_3$, driving contraction; endothelial $ET_B$ additionally releases nitric oxide that raises cyclic GMP for relaxation. Neither single cyclic nucleotide fully represents the mechanism.
Step 4: Because the cleanest physiological choice (calcium/phosphoinositide) is not offered cleanly, we defer to the printed letter.
\[\boxed{cAMP\ (per\ printed\ key)}\]