Lesson 21 - How cells change phenotypes_2025

Page 1: Overview

Rapid Signal Transmission: G-protein signaling at the retina allows the eye to rapidly respond to light.
Adaptation to Light: The eye adjusts to dim and bright light conditions to maintain optimal vision.

Function: Nitric oxide (NO) triggers relaxation of smooth muscle cells, impacting blood flow.

Neuronal Circuitry: Different stimulants affect neuronal circuitry, primarily affecting dopamine levels.
Cholera Toxin: A classic example illustrating how toxins can disrupt signaling pathways.

Olfactory GPCR Receptors:
- Affiliated with multiple odorant molecules.
- Individual neurons have varied GPCR repertoires leading to unique smell signatures.
- Odorant receptors are located on cilia of olfactory neurons in the nasal cavity.
Olfactory Neuronal Signaling:
- Activation: GPCR activates G-alpha, stimulating adenylyl cyclase (AC), resulting in cAMP production.
- Depolarization: cAMP opens Na+ channels, triggering action potentials.

Types of Cells:
- Cone Cells: Detect RGB colors.
- Rod Cells: Sensitive to light intensity.
Rod Cell Functionality:
- In darkness: Stable firing via cGMP-gated Na+ channels, releasing neurotransmitters to optic nerves.
- Light exposure: Inhibition of firing occurs due to changes in membrane potential.

GPCR activates transducin (G-alpha), leading to cGMP phosphodiesterase activation which decreases cGMP levels, closing Na+ channels and inhibiting synaptic neurotransmitter release.

Speed:
- Image recognition occurs in about 13 milliseconds, processing roughly 75 images per second.
Sensitivity:
- A single photon can cause a 1 mV shift in membrane potential.
- Amplification occurs through multiple stages allowing significant adaptation to varying light intensities.
- Example of response dynamics: From 1 to 10 photons producing outputs from 1 mV to 10 mV.

Chemical Response:
- Taste buds release serotonin when exposed to chemicals.
Taste Types:
- Basic Tastes: Sweet, salty (Na+), sour (H+), bitter.
  - Gated Channels: Salt, Sour, Bitter mediated via electrical signals.
  - GPCR: Bitter (diverse), Sugar, Amino acids processed through Ca++ waves.

Which sense does NOT use GPCR signaling?
- Options: A. Smell, B. Vision, C. Tastes, D. Sound, E. All use GPCR

Rod cells utilize GPCRs in their light-sensing mechanism which influences cyclic GMP phosphodiesterase action and light response.
Effects of drugs on rod cells will vary on their action type, altering the light-sensing capacity.

Control Mechanism:
- Acetylcholine (Ach) interacts with GPCR, leading to calcium ion release which activates nitric oxide synthase.
- NO diffuses, binds to guanylyl cyclase in muscle cells, promoting relaxation via cGMP.
Drugs Impacting Blood Pressure:
- Examples: Nitroglycerin, Viagra (inhibit cGMP phosphodiesterase).
Paracrine Signaling:
- Important for coordination among cell types in tissues/organs.

Which situation could lead to smooth muscle relaxation independent of acetylcholine?
- Various options involving defects in guanylyl cyclase and other pathways.

Adderall/Cocaine:
- Related to dopamine levels affecting attention and neuronal firing.
- Inhibit reuptake of dopamine, enhancing synaptic activity.
Cholera Toxin:
- Modifies G-alpha, preventing GTPase activity, causing excessive cAMP and chloride ion channel activity leading to diarrhea.
Caffeine:
- Competes with adenosine GPCRs, reducing sleep-promoting effects, influencing dopamine activity.