Final answer:
Nitric oxide (NO) diffuses directly across the plasma membrane and binds to intracellular receptors rather than extracellular ones. Its role includes causing vasodilation through smooth muscle relaxation, highlighted by its use in medications like nitroglycerin and Viagra.
Step-by-step explanation:
When considering the mechanisms of action for the signaling molecule nitric oxide (NO), it is essential to understand its unique properties as a gaseous ligand. Unlike other signaling molecules, NO can diffuse directly across the plasma membrane due to its gaseous state. This direct diffusibility implies that nitric oxide does not primarily bind to extracellular receptors like G-protein-linked receptors or receptor tyrosine kinases but instead interacts with intracellular targets.
Nitric oxide's role in the body includes inducing relaxation in smooth muscle tissues, acting as a paracrine chemical that can cause vasodilation. A well-known application of NO's function is seen in the action of nitroglycerin, which is used to treat heart conditions by releasing NO to dilate blood vessels and improve blood flow. Additionally, NO acts over very short distances due to its short half-life, emphasizing its action within the cell or in nearby cells.
An illustrative example of NO's function is in the prescription medications for erectile dysfunction, such as Viagra, where pathways affected by NO lead to vasodilation and hence erection. Therefore, considering the function and characteristics of nitric oxide, it can be inferred that it acts by binding to an intracellular receptor rather than directly interacting with DNA.