Molecular Cell Biology Lecture 22: G Protein-Coupled Receptors III

Flashcards created to review key concepts regarding the role of nitric oxide in molecular cell biology, G protein-coupled receptors, and related mechanisms of smooth muscle contraction and relaxation.

What are the three isoforms of nitric oxide synthase (NOS)?

Endothelial NOS (eNOS), Neuronal NOS (nNOS), and Inducible NOS (iNOS).

How does acetylcholine induce eNOS activation in endothelial cells?

Acetylcholine binds to M3 muscarinic receptors on endothelial cells, activating Gqα which leads to calcium release from the ER and activation of eNOS.

What is the role of nitric oxide (NO) in vasorelaxation?

NO diffuses into smooth muscle cells, activates soluble guanylate cyclase, which increases cGMP and leads to relaxation of the smooth muscle.

What effect does eNOS uncoupling have on nitric oxide production?

eNOS uncoupling results in the production of superoxide (O₂⁻) instead of nitric oxide (NO), which is detrimental to vascular health.

What is the function of acetylcholinesterase at the neuromuscular junction?

Acetylcholinesterase breaks down acetylcholine in the synaptic cleft to terminate muscle contraction.

Describe the consequences of excessive acetylcholinesterase activity at the neuromuscular junction.

Excessive acetylcholinesterase leads to flaccid paralysis, as it breaks down acetylcholine too quickly, preventing muscle contraction.

What is the mechanism of action of Viagra (Sildenafil)?

Viagra inhibits phosphodiesterase-5 (PDE-5), preventing the breakdown of cGMP, thus enhancing smooth muscle relaxation and blood flow to the penis.

What is the relationship between nitric oxide and erectile function?

Nitric oxide is released during sexual stimulation, leading to increased cGMP and PKG activity, which promotes relaxation of smooth muscle and increased blood flow, resulting in an erection.

How does guanylate cyclase contribute to smooth muscle relaxation?

Guanylate cyclase converts GTP to cGMP, which activates PKG leading to decreased calcium levels and increased myosin light chain phosphatase activity, promoting relaxation.

What is the role of calcium in endothelial nitric oxide synthase (eNOS) activation?

Calcium binds to calmodulin, which then activates eNOS, leading to nitric oxide production.