Cell Communication
Dr Safa Abdul Ghani
Overview of Cell to Cell Communication:
• Two basic types of physiological signals:
I.
Electrical : changes in a cell s membrane potential
II.
Chemical : molecules secreted by cells into the extracellular Fluid.
Chemical signals are responsible for most communication within the body.
The cells that receive electrical or chemical signals are called target cells
• Chemical
• Autocrine & Paracrine: Local Signaling
• Endocrine system: Distant, Diffuse Target
• Electrical
• Gap Junction: Local
• Nervous System: Fast, Specific, Distant Target
four basic methods of cell-to-cell
communication:
(1) gap junctions, which allow direct cytoplasmic transfer of electrical
and chemical signals between adjacent cells
(2) contact-dependent signals, which occur when surface molecules on
one cell membrane bind to surface molecules on another cells
membrane
(3) local communication by chemicals that diffuse through the
extracellular fluid
(4) long-distance communication through a combination of electrical
signals carried by nerve cells and chemical signals transported in the
blood
1) Gap Junctions
Protein channels – connexin
Direct flow to neighbor
- Electrical-ions (charge)
- Signal chemicals
2) Contact dependent
signal
CAMs (Cell adhesion molecules)
- Need direct surface contact
- Signal chemical
Direct and local cell-to-cell communication
3)Paracrines and Autocrines (Local
communication)
• Local communication
• Signal chemicals diffuse
to target
• Example: Cytokines
- Autocrine
receptor on same cell
- Paracrine
receptor on neighboring
cells
Direct and local cell-to-cell communication
4)Long Distance Communication: Hormones
• Signal Chemicals
• Made in Endocrine
Cells
• Transported via Blood
• Receptors on Target
Cells
Figure 6-2a: Long distance cell-to-cell communication
4) Long Distance Communication:
Neurons and Neurohormones
• Neurons
Electrical Signal down Axon
Signal Molecule (Neurotransmitter) to Target
Cell
• Neurohormones
Chemical and Electrical Signals down Axon
Hormone Transported via Blood to Target
Figure 6-2 b: Long distance cell-to-cell communication
Long Distance Communication:
Neurons and Neurohormones
Figure 6-2 - Overview
Signal Pathways
• Signal Molecule (Ligand)
• Receptor
• Intracellular Signal
• Target Protein
• Response
Receptor locations
Cytosolic or Nuclear
- Lipophilic ligand enters cell
- Often activates gene
- Slower response
Cell Membrane
- Lipophobic Ligand can't enter
cell
- Outer Surface Receptor
- Fast Response
Figure 6-4: Target
cell receptors
Figure 6-4 (3 of 3)
Membrane Receptor Classes
• Ligand- Gated Channel (Receptor Channel)
• Receptor Enzymes
• G-Protein-Coupled
• Integrin
Figure 6-5
Membrane Receptor Classes
Figure 6-5: Four
classes of membrane receptors
Signal Transduction
Transforms Signal
Energy
Protein Kinase
Second Messenger
Activate Proteins
• Phosporylation
• Bind Calcium
Cell Response
Figure 6-8: Biological signal transduction
Figure 6-6
Figure 6-7
Figure 6-8
Table 6-1
Table 6-2
Figure 6-9
Receptor Enzymes
Transduction
Activation
Cytoplasmic
- Side Enzyme
Example:
Tyrosine Kinase
Figure 6-10: Tyrosine kinase, an example of a receptor-enzyme
G-Protein-Coupled Receptors
Hundreds of Types
Main Signal Transducers
• Activate Enzymes
• Open Ion Channels
• Amplify: Adenyl Cyclase-cAMP
• Activates Synthesis
G-Protein-coupled Receptors
Figure 6-11 - Overview
Figure 6-11, step 1
Figure 6-11, step 2
Figure 6-11, step 3
Figure 6-11, step 4
Figure 6-11, step 5
Figure 6-12 - Overview
Figure 6-12, step 1
Figure 6-12, step 2
Figure 6-12, step 3
Figure 6-12, step 4
Figure 6-12, step 5
Figure 6-5
RECEPTOR CHANNELS
Figure 6-13
Figure 6-14
Novel Signal Molecules
Calcium:
- Channel Opening
- Muscle Contraction
- Enzyme Activation
- Vesicle Excytosis
Nitric Oxide (NO)
- Paracrine: Arterioles
- Activates cGMP
- Brain Neurotransmitter
Modulation of Signal Pathways by Ligands
Multiple Ligands
Agonist
Turn on Receptor
Antagonist
Block Receptor
Activity
Figure 6-17: Agonists
and antagonists
Modulation by Receptors
Multiple Receptors for a Ligand: Epinephrine (adrenaline)
• Alpha Receptor / Vasoconstriction
• Beta Receptor / Vasodilation
Receptor Up-Regulation: Grow More Receptors
Receptor Down-Regulation: Grow Fewer Receptor
• Excess Stimulation
• Drug Tolerance
Endocytosis of Ligand & Receptor
Modulation by Receptors
Figure 6-18: Target
response depends on the target receptor
Homeostasis and “Homeodynamic”
• Cannon's Postulates (Concepts)
• Nervous Regulation of Internal Environment (control blood
volume, blood osmolarity, blood pressure, and body
temperature)
• Tonic Level of Activity (Blood vessel diameter)
• Antagonistic Controls (ex. insulin and glucagon)
• Chemical Signals can have Different Effects on Different
Tissues
Figure 6-19
Tonic Level of Activity (Blood vessel diameter)
Figure 6-20
Antagonistic Controls
Figure 6-21 - Overview
Figure 6-21a
Figure 6-21b
Control Pathways
⮚Maintain Homeostasis
Local–Paracrines (ex.Nitric oxide)
Long-Distance–Reflex Control
• Nervous
• Endocrine
• Cytokines
Control Pathways
Figure 6-22
Reflex Control
Stimulus
Sensory Receptor
Afferent Path
Integration Center
Efferent Path
Effector- Target Cell/Tissue
Response (Feedback Loop)
Figure 6-22: Steps of a reflex
Types of Receptors: Membrane, CNS & Peripheral
Figure 6-23: Multiple meanings of the word receptor
Feedback Loops
• Negative Feedback: Are Homeostatic
Response Slows Stimulation
Return to Optimal Range
• Positive Feedback:
Stimulation Drives more Stimulation
• Feed Forward:
Prepares Body for Change
Feedback Loops
Are Not Homeostatic
:
Negative and positive feedback
Feedback Loops
Figure 6-28
Complexity and Modulation
of Control Systems
Specificity
Nature of Signal
Speed
Duration
Stimulation
Intensity
Figure 6-30a
Figure 6-30b
Figure 6-30c
Table 6-4
Figure 6-31 - Overview
Figure 6-31, step 1
Figure 6-31, step 2
Figure 6-31, step 3
Figure 6-31, step 4
Figure 6-31, step 5
Figure 6-31, step 6
Table 6-5
Summary
Integration of Systems uses: Local, Endocrine and Nervous
Communications
Signals Travel Via: Diffusion, Gap Junctions, Axons, and Blood to
Target Cells
Receptor Types and Functions: Binding, Transduction,
Amplification, Activation, Cell Responses
Receptors are Modulated by: Competition, Specificity, Blocking,
Up– and
Down–Regulation
Concepts of Homeostasis (Homeodynamics)
Reflex Control Pathways, Types, Feedback and their Regulation