The figure below shows the pathway through which nitric oxide (NO) triggers smooth muscle relaxation in a blood-vessel wall. Which of the following situations would lead to relaxation of the smooth muscle cells in the absence of acetylcholine? acetylcholine NO bound to guanylyl cyclase activated NO synthase NOS arginine . GTP NO cyclic GMP APIO RELAXATION OF SMOOTH MUSCLE CELL RAPID DIFFUSION OF NO ACROSS MEMBRANES endothelial cell smooth muscle cell a drug that functions as an antagonist for acetylcholine. a drug that blocks an enzyme involved in the metabolic pathway from arginine to NO a smooth muscle cell that has a defect in guanylyl cyclase such that it cannot bind NO a muscle cell that has cyclic GMP phosphodiesterase constitutively active a muscle cell that has a defect in guanylyl cyclase such that it constitutively converts GTP to cyclic GMP